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1AS COMPUTER 🤖🤖 SCIENCE ⚗⚗
2Revision notes 📓📓📓
3RI Green 🤢
4
5Abstract
6A set of revision notes 📓📓 for the WJEC AS level examination. Note 🔣🔣🔣 that this ⬆ document only
7covers the material from Mr 🇲🇷🇲🇷🇲🇷 Green’s lessons.
8AS Computer 🤖 Science ⚗⚗
9pg. 1
10TABLE OF CONTENTS
11Key 🔑 Concepts ...................................................................................................................................................................... 2
12Number systems................................................................................................................................................................. 3
13Character Sets..................................................................................................................................................................... 4
14Components of a Computer 🤖🤖🤖 System................................................................................................................................... 5
15Input ⌨ and Output devices................................................................................................................................................... 5
16The Central 🇨🇫🇨🇫🇨🇫 Processing Unit................................................................................................................................................ 8
17Computer 🤖 Architecture..................................................................................................................................................... 10
18Software 👩‍💻👩‍💻 ........................................................................................................................................................................... 13
19Programming 📺 Paradigms .................................................................................................................................................. 20
20Translation........................................................................................................................................................................ 23
21Databases ......................................................................................................................................................................... 26
22Other types of Business 👩‍💼👩‍💼 Software 👩‍💻..................................................................................................................................... 27
23Networking ....................................................................................................................................................................... 30
24Software 👩‍💻👩‍💻 Development.................................................................................................................................................. 35
25AS Computer 🤖 Science ⚗⚗
26pg. 2
27AS LEVEL COMPUTING 🖥🖥🖥 REVISION NOTES 📓📓📓
28KEY 🔑 CONCEPTS
29Analogue - analogue is 🈶 a continuous varying signal 🚥
30Digital signal 🚥🚥 – consists of discrete (bit) patterns which have 🈶🈶🈶 two ✌✌✌ states 🇫🇲🇫🇲🇫🇲.
31Analogue to digital conversion - digital transmission is 🈶 preferred as it is 🈶 less ➖➖➖ likely to suffer
32corruption/degradation/interference. Analogue signals are sampled at regular intervals. Values (e.g.
33amplitude of wave 👋) are records in binary format
34Binary vs 🆚🆚🆚 digital data 💽💽💽 - all data 💽💽💽 in the computer 🤖🤖🤖 is 🈶 stored in binary format, because digital computer 🤖
35systems are built 👷‍♀️ using transistors in which electricity 💡💡 can have 🈶 two ✌✌ states 🇫🇲🇫🇲 – flowing and not flowing.
36AS Computer 🤖 Science ⚗⚗
37pg. 3
38DATA 💽 REPRESENTATION
39NUMBER SYSTEMS
40BINARY AND HEXADECIMAL
41Binary - a number system in base 2, which counts in 2s, which uses 2 digits (don't say 🗣🗣🗣 two ✌✌ numbers 💯💯!).
42Hexadecimal - a number system in base 16, which counts in group 👥👥👥 of 16s, which uses 16 digits (don't say 🗣🗣
43sixteen numbers 💯!). Relationship to binary to hexadecimal is 🈶 that groups of four 4️⃣4️⃣4️⃣ binary bits (from the right 👉👉)
44give hexadecimal digitals when ⏰ converted into decimal values. Use letter ✉️✉️✉️ A for 10, B 🅱️🅱️ for 11, C for 12, etc
45NEGATIVE NUMBERS 💯
46Two’s Compliment - system for denoting negative numbers 💯 in binary. To convert ➡ to 2s compliment, "flip
47each bit" in the byte and add 1. The same process (flip bits and add 1) converts from negative to positive
48Sign ⛎ and Magnitude – in bytes, one 1️⃣1️⃣ bit represents the sign ⛎, the other bits represent the magnitude
49(size/”bigness”) of the number).
50BINARY ADDITION âž•âž•âž•
51Add corresponding values: when ⏰ adding 1+1 and 10+1, carry the left 👈👈-most digit to the right 👉👉👉.
52Overflow – caused when ⏰ adding two ✌✌ values. The resulting number is 🈶 too large to represent in the available
53storage (e.g. 9 bit number cannot be stored in a single 8-bit byte.
54FLOATING POINT 🈯🈯 NUMBERS 💯
55- two ✌ parts: exponent and mantissa (e.g. 3.14 x ❌❌❌ 106. mantissa=3.14, exponent=6). Similarly in binary. both
56stored in 2s compliment form. Binary point 🈯🈯 is 🈶 not indicated – between left 👈👈👈 most pair 👫👫👫 of digits.
57Advantages – greater range of numbers 💯💯 can be stored.
58Problems: values are not normally stored with complete accuracy, requires more ➕ complex processing, no 😣😣
59exact representation of zero 0️⃣
60NORMALISATION - process of converting numbers 💯 into a "normal form" means we can express 🚛🚛🚛 very large
61and small numbers 💯💯.
62Binary place 🏆🏆🏆 is 🈶 always 🕔 between the first 🥇 and second 🥈 digits from the left 👈👈👈, so this ⬆ number is 🈶 0.1000 x ❌❌ 2100,
63where 🤷 0.100 💯💯💯 and 100 💯💯💯 are both binary numbers 💯💯💯.
64Numbers 💯 are always 🕔 stored in 2s compliment format.
65Numbers 💯 starting "10" are always 🕔 negative. Other numbers 💯💯 are positive
66Converting Binary to decimal.
67Divide 🈹 into two ✌ parts mantissa and exponent.
68AS Computer 🤖 Science ⚗
69pg. 4
70The mantissa (in binary) is 🈶 _________________, the exponent (in binary) is 🈶 _______________
71Is 🈶 mantissa positive? (Does it start 🆕🆕 “01”?)
72Is 🈶 exponent mantissa positive? (Does it start 🆕 “01”?)
73Convert âž¡ exponent to decimal format.
74(If negative convert ➡ to absolute value using two’s compliment, then prefix with a – sign ⛎⛎).
75Move the binary point 🈯🈯🈯 in mantissa the correct number of places.
76Convert âž¡ mantissa from binary to decimal.
77EXAMPLE CONVERSION
78Convert âž¡ 01000100 to denary.
79Mantissa = 01000, exponent = 100 💯💯💯
80Exponent starts "10" so this ⬆ number is 🈶 negative.
811002 is 🈶 410.
82Therefore value is 🈶 -4
83Mantissa – binary point 🈯🈯🈯 place 🏆🏆🏆 needs to be moved 4 positions to the left 👈👈👈 (left 👈👈👈 for negative).
84Mantissa becomes 0.0001
85Decimal value is 🈶 ½ multiplied by 2-4 = 1/32 = 0.03125
86OR
87Exponent 1002 represents -4
88mantissa 0.12 represents ½
89value is 🈶 ½ multiplied by 2 -4 = 1/32 (= 0.03125).
90ACCURACY AND PRECISION
91If length 📏📏 of mantissa is 🈶 increased (e.g., 10 bits to 11), then accuracy is 🈶 improved due to the extra bit storing
92additional values, however the range of values represented will be reduced, since there is 🈶 one 1️⃣1️⃣1️⃣ bit less ➖➖➖ to
93store range information 💁💁💁.
94CHARACTER SETS
95Character Set - the characters 🔣 recognised by the computer 🤖/operating system. Each character is 🈶 assigned a
96unique binary code 💻. Often linked to characters 🔣 on 🔛🔛🔛 keyboard ⌨. Commonly ASII codes are used assigning 7 or
978 bits/byte. Alternatives include Unicode - use 16 bits per character.
98ASCII - American 🗽🗽🗽 Standard Code 💻 for Information 💁 Interchange. Each of 128 characters 🔣 is 🈶 assigned a unique
99code 💻. Each character in this ⬆ character set can therefore be represented by in one 1️⃣1️⃣1️⃣ byte - seven 7️⃣ bits for the
100ASCII code 💻, learning one 1️⃣ bit available for parity checking.
101AS Computer 🤖 Science ⚗⚗⚗
102pg. 5
103HARDWARE COMPONENTS
104COMPONENTS OF A COMPUTER 🤖🤖🤖 SYSTEM
105Hardware – the physical components that make up ☝☝☝ a computer 🤖🤖🤖 system.
106Software 👩‍💻 – programs and data 💽💽💽 (groups of instructions to the CPU) used to make the hardware
107work 💼💼/produce useful results.
108System software 👩‍💻👩‍💻👩‍💻 - Systems software 👩‍💻 controls the hardware/makes the system useable by the operator.
109Peripheral (device) – hardware device that is 🈶 external to the CPU. Examples: keyboard ⌨⌨⌨, mouse 🐭🐭, VDU, etc.
110Application 📝 software 👩‍💻👩‍💻 - applications software 👩‍💻👩‍💻 allows the user 👤👤 to carry out 🏎🏍 a useful task (which would need
111to be carried out 🏎🏍 even if computers did not exist).
112INPUT ⌨ AND OUTPUT DEVICES
113Input ⌨ device – hardware device used to load 📂📂📂 data 💽💽💽 into a computer 🤖 system. Examples include: keyboard ⌨⌨⌨,
114mouse 🐭🐭🐭, MICR, OCR, bar 🎯🎯🎯 code 💻 readers, OMR, etc.
115Keyboard ⌨⌨ - used to enter ↩️↩️↩️ text 📖 based data 💽 into the computer 🤖🤖🤖 e.g. to type ⌨ in a magazine article into a
116DTP document.
117Concept keyboard ⌨⌨ - has restricted 🈲🈲 characters 🔣🔣🔣, few keys, simplifies input ⌨ leading to fewer data 💽💽💽 entry 🚪🚪🚪
118errors. Meaning of keys may alter depending on 🔛 the stage 🎦 in the input ⌨⌨⌨ cycle 🔄🔄🔄. May offer instructions
119to the user 👤👤👤 to help 🆘 with key 🔑🔑🔑 use. Keys may be touch sensitive, embedded, protected from
120weather 🌂/vandals. Braille keys may be used to help 🆘 the blind 🦇🦇🦇.
121Pointing device - mouse 🐭🐭, track pad, joystick 🕹 – allows user 👤 to select and activate items within a GUI.
122Can provide information 💁 on 🔛🔛🔛 movement (e. direction ☝☝☝ and speed 🚅🚅🚅). Examples: mouse 🐭, trackpad 🖲🖲,
123joystick 🕹, etc.
124Joystick 🕹 – alternative to mouse 🐭🐭🐭. Same job 💼 as mouse 🐭, etc. Advantage does not require flat
125surface, works in zero 0️⃣ gravity, etc.
126Trackpad 🖲/ trackerball, touchpad - can more ➕➕ easily be fitted into a small device like 😄 a laptop 👩‍💻👩‍💻
127computer 🤖🤖. Unlike mouse 🐭, does not require a flat space 👩‍🚀, trackpad 🖲🖲/ball, etc to move mouse 🐭.
128Scanner/digital camera 🤳🤳🤳 - used to load 📂📂 images and artwork into computer 🤖🤖🤖. Image is 🈶 captured
129optically, then image is 🈶 digitised to create 🔨🔨🔨 a graphic image file.
130Barcode scanner – Laser/infra red 👹👹/light 🎃 used. Reflections show 📺📺 up ☝☝☝ (thickness) of lines.
131Guide lines to allow reading at an angle. Check digit calculation âž•âž•âž• done for immediate
132checking of reading. Start 🆕 and stop ✋ codes to decide direction ☝ of reading to allow reversal of
133bars 📶📶
134OCR - (Optical Character Recognition) used to read 🛋 paper 🖨🖨🖨 based text 📖 documents 💼, and load 📂📂 these
135into the computer 🤖🤖 without the need to type ⌨⌨⌨ in data 💽💽💽.
136MICR (magnetic ink 🖨🖨🖨 character recognition) - used with bank 🏦 cheques allows fast ⚡ and accurate
137reading of data 💽💽💽 which contains cheque details.
138AS Computer 🤖🤖🤖 Science ⚗⚗⚗
139pg. 6
140Iris recognition: person 👤's iris is 🈶 optically captured, image is 🈶 digitised and stored in a database. On 🔛
141attempted access, the person 👤's iris image captured again, digitised and compared with database.
142Access is 🈶 allowed if records match the scanned iris.
143NB Speech 💭 recognition is 🈶 not an input ⌨⌨⌨ device – it is 🈶 done in software 👩‍💻👩‍💻, which uses a sound 👂 file
144collected with a microphone 🎤🎤. Software 👩‍💻 reads the sound 👂👂👂 wave 👋👋👋 and identifies known wave 👋👋 forms that
145correspond to words 🆔🆔🆔.
146Advantages - speeds up ☝ text 📖 input ⌨/ faster than typing. Can be used by someone who 💁 is 🈶 unable to
147type ⌨⌨. May help 🆘 to avoid RSI. Allows user 👤 to simultaneously do some other task e.g. drive car 🚌.
148Problems - high 🆙🆙🆙 background noise 🔊 stops sound 👂👂 recognition. Cold 🤒 / sore throat, etc., affect the
149voice.
150Input ⌨⌨⌨ = sound 👂👂👂 file, output = text 📖 steam.
151Similarly, handwriting recognition is 🈶 done in software 👩‍💻. Graphics shapes are compared to reference
152images to identify letters/symbols 🔣🔣🔣. Advantages: quicker / easier for user 👤👤👤 than typing. No 😣😣 need to
153learn 🎓 to type ⌨, more ➕➕➕ natural feel, “natural” form of input ⌨⌨⌨. Avoids bulky keyboard ⌨⌨⌨ – good 👌👍🏾 for confined
154spaces. Disadvantages – incorrect recognition of text 📖.
155Input ⌨⌨ = graphic image, Output - text 📖
156Output device – hardware device used to display 💻💻 the results of processing. Examples: VDU (video 📼 display 💻💻💻
157unit), printer 🖨🖨🖨, plotter, projector, etc.
158Screen 💻💻💻/monitor 💻💻💻/VDU - video 📼📼📼 display 💻 unit - used to display 💻💻💻 data 💽💽 in a visible form, on 🔛 a screen 💻 to the
159user 👤.
160Projector - used to display 💻💻💻 the output from the computer 🤖🤖🤖 to a large audience.
161Printer 🖨🖨/inkjet printer 🖨🖨🖨/laser printer 🖨 - used to produce hard-copy, paper 🖨🖨 based output of computer 🤖
162system output.
163Colour printer 🖨/inkjet - used to produce (high 🆙🆙 quality) paper 🖨 based proofs of documents 💼.
164Storage device – hardware device used for long-term storage of data 💽💽💽. Needed because the contents of
165memory are lost 🏳 when ⏰ power 🔋 switched off, size of memory is 🈶 usually insufficient for all programs and data 💽💽💽
166required, and needed to export/import data 💽💽💽. Storage devices are non-volatile meaning data 💽 is 🈶 not lost 🏳🏳🏳
167when ⏰ power 🔋🔋🔋 is 🈶 switched off (unlike RAM 🐏 which is 🈶 volatile). Examples include: Magnetic media such as hard
168and floppy disc 💿 drives, optical media such as CD 💿-ROM and DVD 💿💿-R, and solid-state devices such as USB “pendrives”.
169DO NOT CONFUSE HARD-DISK 💽 and MEMORY,
170THEY ARE NOT THE SAME THING.
171DO NOT USE THESE WORDS 🆔 INTERCHANGEABLY.
172Magnetic:
173Hard disk 💽 - stores files/software 👩‍💻/operating system.
174Floppy disk 💽💽 - stores backups of important files to transfer work 💼💼💼 between machines.
175AS Computer 🤖🤖 Science ⚗
176pg. 7
177Optical media: CD 💿-ROM, CD 💿-RW 🇷🇼🇷🇼, DVD 💿💿💿 and DVD 💿💿-RW 🇷🇼🇷🇼. Easy to access. Most users are familiar with CD 💿💿/DVD 💿
178technology 📱📱📱. Very cheap per unit of storage. Robust and portable.
179CD 💿💿💿-ROM and DVD 💿💿💿-ROM - used to import software 👩‍💻👩‍💻👩‍💻, store encyclopaedia /databases /video 📼 /music 🎤🎤
180/films 🍿 /backup files. Always 🕔 include the suffix when ⏰ talking about optical disks
181CD 💿💿-RW 🇷🇼 and DVD 💿-RW 🇷🇼 –writeable CD 💿💿/DVD 💿 media, allow backup and transport 💺💺💺 of data 💽💽
182CD 💿-ROM - Compact Disk 💽💽💽, read 🛋🛋-only. Removable disc 💿💿💿 storage media. Contents is 🈶 READ 🛋🛋-ONLY and
183CANNOT CHANGE 📈. Allows data 💽💽💽 transferred between machines. Used to hold user 👤👤👤
184software 👩‍💻👩‍💻, operating system files (for installation), and applications programs (such as an
185encyclopaedia).
186Solid state storage
187USB pen 🖊/Flash/Thumb drive – small, portable solid state storage device. Allows easy transport 💺💺 of
188data 💽. Read 🛋🛋🛋/write ✍ storage. Can hold large amount of data 💽💽. Quite cheap per unit of storage. Robust
189SSD – Solid state device – uses NAND based “Flash” memory to store data 💽💽. No 😣 moving 📦 parts –
190therefore rapid access to data 💽💽. Therefore fragmentation of files is 🈶 not a problem ⚠️. Defragmentation
191will not improve device performance. Limited lifespan.
192Magnetic stripes 🦓🦓🦓 - used on 🔛🔛 bank 🏦 card, etc to store details of account, etc. Read 🛋🛋 by a card reader to access
193details.
194AS Computer 🤖🤖🤖 Science ⚗⚗⚗
195pg. 8
196THE CPU
197THE CENTRAL 🇨🇫🇨🇫🇨🇫 PROCESSING UNIT
198CPU – Central 🇨🇫🇨🇫 Processing Unit - performs the processing of instructions issued by programs.
199ALU – arithmetic logic unit. Processes and manipulates data 💽💽💽. Carries out 🏎🏍 arithmetic operations and
200logical comparisons. All input ⌨⌨/output passes through the ALU. Allows the processor to
201communicate with the outside world 🌎🌎.
202Control Unit – CPU component that manages execution of instructions. coordinates the rest 😪 of the
203processor, manages execution of instructions, controls movement of data 💽, synchronises devices, is 🈶
204controlled by a clock ⌛, and sends timing pulses to other parts of the processor.
205Registers – Very fats storage on 🔛 the CPU. Stores data 💽💽💽 and control information 💁 for a specific purpose.
206Examples of registers include the PC, MAR, MDR, CIR, accumulator, etc.
207Special 🌟 purpose registers – these are controlled by the circuits of the CPU
208PC - Program 📺📺📺 Counter – indicates address of next ⏭⏭ instruction. Controls the sequence in which the
209instructions/order 📑 in which instruction are retrieved/executed. It is 🈶 incremented at end 🔚🔚 of fetch
210phase, but can be altered as the result of a jump 🕴 instruction
211CIR - current instruction register - stores the instruction currently being worked on 🔛🔛🔛
212MAR - Memory Address Register – used in transferring data 💽💽 between CPU and memory. Stores the
213memory address being accessed read 🛋🛋🛋/written.
214MDR - Memory Data 💽💽💽 Register - stores the data 💽💽 being transferred to or from memory
215ACCUMULATOR – store results of calculations.
216General 🤷 Purpose registers - available to machine 🤖🤖 code 💻 programmers to store data 💽.
217Bus 🚌🚌🚌 - electrical circuits linking components inside the computer 🤖🤖, used to carry data 💽💽💽, address or control
218signals between computers.
219Data 💽 bus 🚌🚌🚌 - bus 🚌 used to carry data 💽💽💽 between components inside the computer 🤖 e.g. between the CPU
220and memory unit. The message 💬💬 sent down ⬇⬇ this ⬆ bus 🚌 is 🈶 the actual data 💽 which is 🈶 being/has been
221processed. Used in conjunction with the address bus 🚌🚌🚌.
222Address bus 🚌🚌 - bus 🚌🚌 used to carry addressing information 💁💁 between the CPU and memory unit. The
223data 💽💽 indicates the memory location 🗺🗺 into/from which data 💽 should be read 🛋🛋🛋/written. The data 💽 to be
224written to this ⬆ location 🗺/is 🈶 read 🛋 from this ⬆ location 🗺, will travel 🚋🚋 along the data 💽💽💽 bus 🚌🚌🚌.
225Control bus 🚌🚌 - bus 🚌🚌 used to carry control signals between CPU components and the control unit of
226the CPU. Used to coordinate activities within the CPU.
227AS Computer 🤖🤖 Science ⚗
228pg. 9
229MEMORY, BUFFERS AND INTERRUPTS
230MEMORY
231Memory (also known as memory unit) – RAM 🐏🐏🐏 chips 🍟🍟🍟 used to stores in-use data 💽💽 and currently executing
232program 📺 instructions.
233RAM 🐏 – random 🎲 access memory. Computer 🤖 memory, stored on 🔛 a micro-chip fixed in the computer 🤖🤖🤖
234that is 🈶 used to hold in-use data 💽💽💽 and executing program 📺 instructions. Contents lost 🏳 when ⏰ power 🔋 is 🈶
235switched off. Contents can be changed 📈. Volatile storage. Sometimes called primary memory.
236ROM – read 🛋-only memory – contents cannot change 📈. Computer 🤖🤖 memory, stored on 🔛🔛🔛 a
237semiconductor chip. The chip is 🈶 fixed into one 1️⃣1️⃣1️⃣ machine 🤖🤖🤖 and typically stores the computer’s start 🆕🆕🆕-up ☝☝
238(boot 👢 file) programs (do not say 🗣🗣🗣 BIOS!). Non-volatile storage.
239Boot 👢👢-file – stored in ROM. Needed immediately computer 🤖 is 🈶 powered on 🔛🔛🔛. Start 🆕 initiate load 📂 of operating
240systems.
241BUFFERS AND INTERRUPTS
242Buffers – area of memory (RAM 🐏) outside the processor used as a temporary store for data 💽💽 being sent to a
243slower device. Allows the CPU to continue ⏩⏩ with other tasks, while data 💽💽💽 is 🈶 sent to the slower device. Used to
244compensate for speed 🚅🚅🚅 differences to allow processor to continue ⏩⏩ with other task. Used in conjunction with
245interrupts. Buffers may be used to load 📂 other buffers (called double buffering).
246Data 💽💽💽 transfer using buffers (e.g. from primary memory to secondary storage) - data 💽 sent to buffer from primary
247memory. Interrupt sent when ⏰ buffer is 🈶 full 🈵🈵🈵, buffer is 🈶 then emptied to storage device, at slower speed 🚅, to
248accommodate device. CPU continues on 🔛 other work 💼💼. When ⏰ buffer is 🈶 empty 🈳, interrupt is 🈶 sent to processor to request
249buffer refill. When ⏰ priority of interrupt is 🈶 highest of queued interrupts, more ➕➕ data 💽💽💽 will be loaded into the buffer.
250Process is 🈶 repeated until data 💽💽 transfer has completed, when ⏰ a final interrupt sent to indicate completion.
251Interrupts – a signal 🚥🚥 sent generated by a device or sofwtare, sent to the processor, to request processor
252time ⌚. May cause 🎗🎗 a break 💔💔 in the execution of the current routine Interrupts have 🈶🈶🈶 priorities. Example: to
253signal 🚥🚥🚥 that a printer 🖨 has printed all data 💽💽💽 in the buffer, more ➕➕➕ data 💽💽💽 is 🈶 needs to be loaded into the buffer.
254Examples of interrupts:
255 Hardware or Software 👩‍💻 fault
256 Input ⌨/output device requesting attention e.g. printer 🖨🖨🖨 out 🏎🏍 of paper 🖨🖨🖨 / requesting
257 more ➕➕➕ data 💽💽💽 / key 🔑🔑 press 🗞🗞🗞 / mouse 🐭🐭 click 🖱
258 User 👤👤 interrupt e.g. <ctrl> <break 💔💔>
259 Operating system generated interrupt e.g. end 🔚🔚🔚 of time ⌚⌚⌚ slice
260 Run 🏃 time ⌚⌚ error 🚨 e.g. division by zero 0️⃣
261Interrupt processing - compare the priority of the interrupt to that of current task. If this ⬆ interrupt's priority
262is 🈶 lower it will be placed in a queue in a position appropriate to the task's priority. If its priority is 🈶 higher, the
263O/S suspends the current task - contents of the processors registers will be stored, and the interrupt
264processed according to. Its interrupt service 🛎 routine. When ⏰ this ⬆ completes, the original processing is 🈶
265resumed.
266AS Computer 🤖🤖 Science ⚗
267pg. 10
268COMPUTER 🤖🤖🤖 ARCHITECTURE
269COMPUTER 🤖🤖🤖 ARCHITECTURE
270VON NEUMANN ARCHITECTURE
271Single CPU control unit. Data 💽 and instructions are stored together (in memory). Sequential processing:
272Instructions carried out 🏎🏍 in linear sequence (fetch, decode, execute, reset). Programs follow a specific
273algorithm where 🤷 the order 📑📑📑 of instructions changes the outcome of the program 📺📺📺. This ⬆ architectures suits ♠️♠️♠️ any
274example where 🤷 the outcome is 🈶 dependent on 🔛🔛 steps 🚶‍♀️🚶‍♀️ being taken in a defined order 📑📑📑 e.g. the solution to a
275formula 🏎. Slow 🐌🐌 processing due to use of a single CPU/control unit
276FETCH-DECODE-EXECUTE CYCLE 🔄🔄🔄
277Instructions are executed in sequence, during execution the registers are used in the following manner:
278FETCH
279 Contents of PC -> MAR. Address of the next ⏭ instruction is 🈶 read 🛋🛋🛋 from the PC and copied into the MAR;
280 Memory unit is 🈶 read 🛋 and the required location’s data 💽💽💽 is 🈶 copied to -> MDR.
281 Contents of MDR -> CIR. Value in MDR is 🈶 written into CIR.
282 PC is 🈶 incremented
283DECODE
284The control unit examines the contents of the CIR. Actions will depend on 🔛 the operator, for example:
285For branch 🎋/jump 🕴 instructions, the address (for the jump 🕴) is 🈶 obtained from operand in the CIR. This ⬆ is 🈶
286copied into PC.
287For commands reading/writing 🖊🖊 memory the memory unit, the address will be copied to MAR. Data 💽💽💽
288may need to be retried from the memory unit (and will be read 🛋 from MDR).
289EXECUTE
290 The instruction in CIR is 🈶 now executed.
291REGISTERS
292Small pieces of very fast ⚡⚡⚡ access storage, on 🔛 CPU, used control its execution. These include general 🤷 purpose
293and special 🌟 purpose registers:
294Special 🌟 Purpose registers – controlled by electronics of the CPU:
295 PC – program 📺📺📺 counter. A register that holds the address of the next ⏭⏭⏭ instruction to be executed.
296Increments on 🔛 every fetch operation, can also changes to indicate the next ⏭⏭⏭ location 🗺🗺🗺 when ⏰ a BRANCH 🎋
297operation takes place 🏆🏆🏆.
298 MAR – memory address register. The address of the data 💽💽 (instructions) to be fetched/of the next ⏭
299location 🗺🗺🗺 to be accessed.
300AS Computer 🤖 Science ⚗
301pg. 11
302 MDR – Memory Data 💽💽💽 register. Temporary store for data 💽💽💽/instruction being transferred to/from
303memory. Acts as a buffer, to compensate for different speeds.
304 Accumulator – a register in the ALU, that stores intermediate results and data 💽💽 currently being
305processed. Used for arithmetic/logic. Input ⌨ and output passes through the accumulator, used for
306temporary storage, before data 💽💽 is 🈶 sent to the memory unit.
307 CIR – Current Instruction Register. The address of the instruction currently being executed.
308PARALLEL PROCESSING
309Simultaneous use of more ➕➕➕ than one 1️⃣1️⃣1️⃣ CPU to execute the instructions of a single job 💼 (at the same time ⌚). Jobs
310are divided up ☝☝☝ into smaller tasks, each task being executed simultaneously on 🔛🔛🔛 a separate processor. Results
311from the sub-tasks are combined to produce the overall results for the program 📺📺.
312ï‚· Advantages: faster processing of the workload, different parts of a process can be executed
313simultaneously; complex tasks are performed more âž•âž•âž• efficiently.
314ï‚· Disadvantages: programs needs to be specially written with complex processing to adapt the
315sequential algorithm. Not suitable for some programs, as there are complex communications needed
316between parts of the jobs on 🔛🔛 different processors; special 🌟 signals or flags 🎏🎏🎏 will need to be used by the
317programs to allow the separate parts of the job 💼💼💼 to communicate with one 1️⃣ another.
318 Typical uses: used in time ⌚⌚ dependent operations which require large amounts of processing time ⌚
319such as weather 🌂🌂🌂 forecasting, complex mathematical modelling (e.g. running 🏃‍♀️ climate change 📈 models),
320calculating prime 2️⃣ numbers 💯💯💯.
321CO 🇨🇴🇨🇴🇨🇴-PROCESSOR
322A component added to the central 🇨🇫🇨🇫🇨🇫 processor, improves speed 🚅 by performing certain tasks e.g. maths coprocessor/floating-point 🈯🈯
323accelerator.
324ARRAY PROCESSOR
325A processor that allows any instruction to operate simultaneously on 🔛 multiple data 💽💽 locations, the same
326calculation ➕➕➕ on 🔛🔛 different data 💽💽💽 is 🈶 very fast ⚡.
327PIPELING
328The processor is 🈶 divided into 3 parts. Each part handles one 1️⃣1️⃣1️⃣ of the stages: fetch, decode, execute. Would
329suggest you always 🕔 draw 🎨🎨 a labelled diagram to illustrate this ⬆.
330 Advantage: allows faster processing as more ➕➕➕ than one 1️⃣1️⃣ instruction is 🈶 used at the same time ⌚⌚.
331 Disadvantages: problems occur with jump 🕴 instructions (out 🏎🏍 of sequence) as the pipe has to be
332cleared and the cycle 🔄🔄🔄 restarted.
333RISC – REDUCED INSTRUCTION SET CHIP
334A CPU featuring relatively few instructions and addressing modes make up ☝☝ the CPU’s instruction set. Each
335instruction requires simple electrical circuits, therefore a RISC chip requires simpler electronics than a CISC
336chip, so will be cheaper to procedure and execute the simpler instructions at a higher rate.
337AS Computer 🤖🤖 Science ⚗⚗
338pg. 12
339CISC (COMPLEX INSTRUCTION SET)
340Uses (complex) instructions each of which may take multiple cycles. Single register set , instructions have 🈶🈶
341variable format with many instructions and addressing modes are available. Requires complex electrical
342circuits in CPU: programs run 🏃 more ➕ slowly than RISC due to the more ➕➕ complicated instructions/circuit
343Software 👩‍💻👩‍💻👩‍💻 and Operating Systems 
344AS Computer 🤖🤖 Science ⚗
345pg. 13
346SOFTWARE 👩‍💻 -OPERATING SYSTEMS
347SOFTWARE 👩‍💻
348Software 👩‍💻👩‍💻 - when ⏰ answering questions on 🔛 software 👩‍💻👩‍💻👩‍💻, do not refer to brand ™️ names or trademarks. You should
349use generic names (given in descriptions below: word processor, spreadsheet, operating system, etc) and
350not use words 🆔🆔🆔 like 😄😄 Windows, Word, Excel, PowerPoint, Photoshop, Coral Draw 🎨
351OPERATING SYSTEMS
352Operating system software 👩‍💻👩‍💻👩‍💻 that acts as an interface hardware and applications programs. Controls the
353hardware and manages the system’s resources (see 👁 below). Provides a human 👤👤👤-computer 🤖🤖🤖 interface.
354RESOURCES MANAGED BY THE OPERATING SYSTEM
355 Input ⌨⌨⌨ and output peripherals - manages data 💽💽💽 sent/received from devices. Controls flow of data 💽💽💽 to/from these
356devices. Manages data 💽💽💽 sent to print (spooling).
357 Spooling – (printing over network) - data 💽 is 🈶 stored on 🔛🔛🔛 hard disc 💿💿💿. Document is 🈶 printed when ⏰ printer 🖨🖨🖨 is 🈶 free 🆓🆓🆓 / in
358correct order 📑📑📑 Benefit of spooling - User 👤👤 can carry on 🔛🔛 working 🏗🏗 / log off when ⏰ waiting for job 💼 to print
359 Manages backing store - ensures that data 💽 is 🈶 stored and can be retrieved correctly from any disc 💿💿 drive.
360Creates and maintains filing 🗄 system e.g. FAT – (File Allocation table) or NTFS (“NT” file system). Organise files
361in a hierarchical directory structure.
362 File compression the amount of data 💽💽💽 is 🈶 reduced and the file is 🈶 made smaller. to save 💾 disc 💿 space 👩‍🚀
363 Disc 💿💿💿 defragmentation - fragmented files are split up ☝☝ and stored on 🔛🔛🔛 different parts of the disc 💿. Disc 💿
364fragmentation will slow 🐌🐌🐌 down ⬇⬇ file access speed 🚅. In defragmentation file parts are physically re-arranged on 🔛🔛
365disc 💿 (into the order 📑📑 required for access)
366 Manages memory (RAM 🐏🐏🐏) - ensures memory can be shared, ensures memory is 🈶 protected (i.e. that programs
367and data 💽💽💽 do not corrupt each other), that all programs and data 💽💽, including the operating system itself, are
368stored in correct memory locations
369ï‚· Manages processes (scheduling) - ensures different processes can use CPU and do not interfere with each
370other, cause 🎗🎗 crashes or dead 💀💀💀-locks (A waits for B 🅱️🅱️ while B 🅱️🅱️🅱️ wait 🚏🚏 for A). Uses different scheduling algorithm (e.g.
371round ⭕ robin, shortest burst, multi-level feedback queues, etc). On 🔛🔛🔛 a multi-tasking O/S ensure that all tasks
372appear to run 🏃 simultaneously. Accepts new 🆕 jobs. Loads new 🆕🆕🆕 programs
373 Manages security 🛡🛡 - allows creation and deletion of user 👤 accounts. Allows users to logon and change 📈
374passwords
375AS Computer 🤖 Science ⚗⚗⚗
376pg. 14
377SCHEDULING
378SCHEDULING
379Scheduler – part of operating system. Aims to
380 Ensure that all tasks are processed eventually, by changing 📈 priorities if necessary.
381 Process as many jobs as possible in the least possible time ⌚⌚. NB you must mention time ⌚⌚⌚ taken.
382ï‚· Maximise number of interactive users receiving fast âš¡âš¡âš¡ response times.
383ï‚· Maximise/make efficient use of resources.
384Time ⌚⌚-slicing (or time ⌚⌚⌚-sharing) – using small amounts of CPU time ⌚⌚⌚ (slices) to run 🏃 each program 📺📺 in turn.
385Computer 🤖 switches between jobs/users, using a round ⭕⭕⭕-robin system to poll terminals if required to
386determine whether they need their next ⏭⏭ timeslice. This ⬆ allows each program 📺 to move on 🔛 a small amount,
387and gives the user 👤 the impression that all the programs are running 🏃‍♀️ simultaneously.
388Round ⭕-robin – processes receive time ⌚-slices in sequence, each in turn. After last job 💼💼 has received time ⌚⌚⌚-slice,
389processing of first 🥇 job 💼💼, for one 1️⃣ time ⌚-slice resumes. Gives impression of a single CPU working 🏗🏗🏗 on 🔛 all tasks
390simultaneously.
391Job 💼 Priorities – an alternative method of scheduling task. Used because some jobs are more ➕ urgent than
392others. Priorities are used to maximise the use of the computer 🤖 resources.
393First 🥇 come, first 🥇 served - jobs are processed in the order 📑📑📑 in which they arrived.
394Shortest burst/Shortest job 💼💼💼 first 🥇🥇🥇 – estimates how 🤔 much CPU time ⌚⌚ is 🈶 required. Small jobs are proffered
395timeslices before larger jobs. Perforamcne is 🈶 dependant non accurate assessment of CPU requirements.
396First 🥇 come, first 🥇 served – jobs are dealt with in the order 📑 they arrive. A big job 💼💼 will block others from
397gaining CPU time ⌚.
398MODES OF USE
399Single user 👤 operating system – allows one 1️⃣1️⃣ user 👤👤 at a time ⌚⌚ to use the system. Allocates each user 👤👤 with rights.,
400Keeps user’s files separate.
401Multi-user 👤👤👤 operating system - allows many users to use a single computer 🤖🤖🤖 simultaneously.
402Multi-tasking operating system – operating systems that allows the computer 🤖🤖🤖 to run 🏃 more ➕ than one 1️⃣
403program 📺, apparently simultaneously using time ⌚⌚⌚-slicing (or time ⌚-sharing). Use of separate window for each
404task. For example; plays music 🎤 while writing 🖊 essay.
405Single user 👤👤 operating system – an operating system designed to allow a single user 👤👤👤 to use a computer 🤖🤖.
406Distributed system – data 💽 is 🈶 stored on 🔛 different computers in the computer 🤖🤖 network. Some on 🔛 the server
407and some on 🔛🔛🔛 users of the server - the client computers.
408Batch processing – processing large quantities of similar data 💽💽 in a similar manner. Processing is 🈶 offline (to
409the user 👤). Processing is 🈶 carried out 🏎🏍 when ⏰ CPU not needed for other tasks. Batch gives result at a later time ⌚⌚⌚.
410Used when ⏰ jobs are not time ⌚⌚⌚ sensitive, for large volumes of data 💽💽. Data 💽/jobs require similar processing.
411Does not require user 👤👤👤 intervention.
412Sequential processing - records are stored one 1️⃣1️⃣1️⃣ after another, in order 📑📑📑 of key 🔑🔑. Records are processed in
413order 📑📑. Usually used in conjunction with batch processing
414AS Computer 🤖🤖 Science ⚗⚗⚗
415pg. 15
416Real-time ⌚ processing - data 💽 (records) are processed rapidly on 🔛🔛🔛 receipt. Gives the user 👤 the impression of an
417instant response. Used with time ⌚⌚⌚-sensitive data 💽 e.g. hospital 🚑🚑 life 💓-support 🎗 system.
418On 🔛🔛🔛-line 〰️〰️〰️ processing - allows the computer 🤖🤖 to directly interact with the user 👤👤 while processing is 🈶 taking place 🏆.
419Examples: computer 🤖 games, flight 🛩 simulators, holiday booking system; why 🤔 - because user 👤👤👤 input ⌨⌨⌨ need to be
420processed quickly enough to influence the next ⏭⏭ output of information 💁💁.
421Off-line 〰️ processing - the computer 🤖🤖 devices (e.g. printers and disk 💽💽💽 drives) are not under the direct control of
422the user 👤👤👤/computer 🤖🤖. Examples: payroll, generating bank 🏦🏦🏦 statements, creating utility bills 💸. Why 🤔 - no 😣😣😣 human 👤
423intervention is 🈶 required.
424AS Computer 🤖 Science ⚗⚗⚗
425pg. 16
426TYPES OF SOFTWARE 👩‍💻
427TYPES OF SOFTWARE 👩‍💻👩‍💻👩‍💻
428System Software 👩‍💻👩‍💻 - controls hardware, provides the user 👤👤👤 with an interface to the hardware, provides an
429environment ⛰ in which programs may be run 🏃.
430Application 📝 programs - software 👩‍💻 that performs useful work 💼💼💼. Applications complete work 💼 that needs to be
431performed even it a computer 🤖 is 🈶 not available.
432Utility program 📺📺📺 – extends the functionality of the operating system e.g. backup program 📺📺, disk 💽💽 formatter.
433Device Driver – software 👩‍💻 that allows a particular hardware device to operate. Allows operating system to
434communicate with a specific piece of hardware.
435AS Computer 🤖 Science ⚗
436pg. 17
437USER 👤👤 INTERFACES
438User 👤👤 Interface (or Human 👤👤 Computer 🤖🤖 Interface -HCI) - software 👩‍💻 that allows the user 👤👤 and computer 🤖 system
439to interact. It allows them to communicate
440GUI - a graphical user 👤👤👤 interface. WIMP - uses windows, icons to represent available programs and
441programs, menus and pointers. Advantages: easy to use, icons show 📺📺📺 representation of options.
442Menu interface - presents the user 👤 with a range of choices, choices may provide a range of further
443choices in a tree 🍃🍃🍃 like 😄 manner. Users select choices. Menus can use function keys to select choice or
444can use mouse 🐭🐭 pointers. Simple to use, can restrict options to restrict access. Guides users through
445choices. Can be frustrating for experienced users as it may require many choices to be selected to
446run 🏃 a single command.
447Command line 〰️〰️〰️ interface – commands are typed into system as a series of keywords and
448parameters are entered. Each stands for an instruction to the operating system. Provide full 🈵🈵 access
449to the system. Advantages: quick to use, often used by experienced users. Usually provide
450complete access to all options in the system. Disadvantages - the need to remember syntax,
451“unforgiving" of mistakes.
452Form based interface –screen based inputs. Provides fields for data 💽💽💽-entry 🚪🚪🚪. (e.g. text 📖 box 🍱), user 👤
453enters data 💽, usually input ⌨ is 🈶 validated by form. Can look 👁 like 😄😄 a paper 🖨🖨 form or ask user 👤 questions.
454Ensures no 😣😣 important information 💁💁💁 is 🈶 missing, makes validation simple, used for large quantities of
455similar input ⌨⌨⌨, often will not allow progression if data 💽💽 item not provided. Typical use, data 💽 entry 🚪
456form for database.
457Natural language 🌎 interface user 👤👤👤 enters their commands into the system in their natural language 🌎 (e.g.
458English 🇬🇧🇬🇧🇬🇧). Can be text 📖 based input ⌨, but often used in conjunction with speech 💭💭 recognition software 👩‍💻👩‍💻. Problem ⚠️⚠️⚠️
459can arise as command words 🆔 may be taken as input ⌨⌨⌨ words 🆔🆔🆔 (or vice versa) (e.g. "end 🔚🔚 sentence").
460Pros of natural language 🌎 interface - user 👤👤👤 does not need to structure input ⌨⌨⌨ in any way ↕️↕️ – can communicate
461with system as if with another person 👤👤👤.
462Drawbacks – problems with ambiguity: the natural language 🌎 used by most people 👫👫👫 is 🈶 very ambiguous and
463imprecise. Human 👤👤👤 language 🌎 doesn't tend to conform to set grammar rules 🚷, slang is 🈶 often used. Also
464(English 🇬🇧🇬🇧🇬🇧) language 🌎 is 🈶 changing 📈 System requires very high 🆙🆙🆙 processing power 🔋🔋 and very complex software 👩‍💻👩‍💻. 
465AS Computer 🤖 Science ⚗
466pg. 18 🔞
467TYPES OF SOFTWARE 👩‍💻👩‍💻👩‍💻
468OCR (optical character recognition) - allows text 📖 to be scanned into the computer 🤖.
469Image processing software 👩‍💻👩‍💻👩‍💻 - allows digital images to be prepared or edited for inclusion into documents 💼.
470Generic Software 👩‍💻👩‍💻 - software 👩‍💻👩‍💻👩‍💻 appropriate to many areas, tasks. Comes complete with appropriate
471documentation. Application 📝 is 🈶 appropriate for use in many areas. Examples: word processor, spreadsheet,
472database.
473Word Processor - software 👩‍💻👩‍💻👩‍💻 application 📝 used for processing and formatting text 📖. Features include: text 📖,
474paragraph and page formatting capability, a range of text 📖 styles (fonts), spelling and grammar checking.
475Example: letters to customers.
476Spreadsheet – application 📝 program 📺📺 used typically to manipulate numbers 💯💯💯 e.g. company accounts. Features
477include: data 💽💽💽 is 🈶 represented in a grid layout, formulae, cells referenced by row and columns, ability to sort
478data 💽💽💽, charts, ability to read 🛋🛋🛋 (and write ✍) data 💽💽 in CSV (comma separated variable) format to exchange data 💽💽
479with other programs; formatting. Typical uses: financial 🏦 calculation ➕➕, modelling and simulation.
480Desk Top 🔼🔼 Publishing –for production of high 🆙-quality documents 💼, typically printed documents 💼.
481Presentation 📊📊📊 software 👩‍💻👩‍💻👩‍💻 –creation of multi-media presentations that can combine text 📖, static and animated
482graphics, video 📼📼📼, sound 👂👂👂, etc. Used to make presentations to groups.
483Web authoring – used to produce a website 💯.
484Utility program 📺📺📺 – system software 👩‍💻. Used to perform a commonplace task. Examples:
485Backup software 👩‍💻👩‍💻👩‍💻 - to make a 2nd copy of files, that can be used to recover the working 🏗 copy of the
486data 💽💽💽, if a file/data 💽💽💽 is 🈶 lost 🏳🏳🏳 or corrupted. All data 💽 is 🈶 copied to a second 🥈🥈🥈, safe plac, preferable
487removable storage (e.g. magnetic tape 📽📽).
488File handling/transfer/sorting - to control access to files or storage, and movement of files.
489Error 🚨 checking - to ensure data 💽💽 transmitted is 🈶 not corrupted. Checks data 💽💽 for errors when ⏰ data 💽💽 is 🈶
490moved.
491Virus checker - to continually scan for and remove ❌❌ viruses.
492Formatting, configuring and defragmenting software 👩‍💻👩‍💻 - to organise storage space 👩‍🚀👩‍🚀👩‍🚀
493Peripheral drivers (device drivers) - control peripheral devices.
494Compression Software 👩‍💻 - reduces the size of files (e.g. to save 💾💾 disc 💿💿 space 👩‍🚀, or to increase ➕➕➕ speed 🚅🚅🚅 of
495data 💽💽💽 transmission).
496Recovery 📈 software 👩‍💻👩‍💻/disk 💽 checker/disk 💽💽 scan - to recover or fix 🔧🔧 lost 🏳🏳 or corrupt files.
497Driver programs - allow a peripheral device to work 💼💼 with an operating system/computer 🤖. Contains
498specific commands for that device.
499Compression software 👩‍💻👩‍💻👩‍💻 - reduces data 💽 volume 🔈🔈 while maintaining integrity of data 💽.
500Archiving – removing inactive data 💽 from a computer 🤖🤖🤖 system. Inactive data 💽 is 🈶 data 💽💽💽 that is 🈶 no 😣😣 longer needed
501(e.g. invoice data 💽💽💽 from a previous ⬅️⬅️ year). Process: identify suitable data 💽💽💽 that can be archived, delete ❌❌❌ this ⬆
502data 💽💽💽. Redundant data 💽 will slow 🐌 down ⬇⬇/fill up ☝☝☝ a system. Tends to be carried out 🏎🏍 infrequently. 
503AS Computer 🤖 Science ⚗
504pg. 19
505Backup Media
506 Tape 📽📽📽 – cheap compared to other media. Access speed 🚅 to tape 📽📽 is 🈶 slow 🐌🐌🐌 (as uses serial access), but
507speed 🚅 is 🈶 not a factor for back ⬅️-ups as they are rarely used. Tape 📽 is 🈶 physically small so easy to move
508and store off-site.
509 Removable (external) hard disk 💽 drive – more ➕➕➕ expensive than tape 📽📽📽, but hard-disk 💽💽 is 🈶 relatively fast ⚡,
510so when ⏰ required, access to data 💽 is 🈶 faster. External disk 💽💽💽 is 🈶 quite small so easy to move/store offsite.
511 Cloud ☁️/network backup – remote backup site could be on 🔛 a server (i.e. network backup) or on 🔛🔛🔛 the
512internet 🌐🌐🌐 (i.e. cloud ☁️ backup) which can be shared with other users. Fast ⚡⚡ transfer is 🈶 possible
513(depending on 🔛 network speed 🚅🚅) for both backup and restore. Could be cheaper than either tape 📽 or
514hard-disk 💽 backup. No 😣😣 physical media required. No 😣😣 need to move media off-site as it is 🈶 already
515stored remotely.
516WEATHER 🌂🌂🌂 FORECASTING
517Inputs from thousands of weather 🌂 stations e.g. satellites, balloons, ships etc from huge geographical area /
518whole world 🌎🌎.
519Processing: Requires the processing of a huge amount of data 💽💽💽. Requires comparison with huge amounts of
520historical data 💽💽💽. Requires very complex calculations. Will require large, complex programs. Processing has to
521be done very quickly as weather 🌂🌂🌂 forecasts are no 😣 use if out 🏎🏍-of-date 👫👫👫 and weather 🌂🌂🌂 is 🈶 often extremely
522unstable / chaotic / hard to predict.
523Output: very high 🆙🆙🆙 graphics capabilities will be needed for e.g. TV 📺 weather 🌂🌂 forecasting programmes where 🤷
524viewers will expect to see 👁 changing 📈 weather 🌂 patterns displayed graphically.
525AS Computer 🤖🤖🤖 Science ⚗
526pg. 20
527PROGRAMMING 📺 PARADIGMS
528PROGRAMMING 📺 PARADIGMS
529Visual Programming 📺 - High 🆙 level language 🌎. Might be used for developing 👩‍💻 in a GUI / windowed / event 🎫
530driven environment ⛰. Such applications lend themselves naturally to visual programming 📺 and would be very
531difficult in a text 📖 based programming 📺 environment ⛰⛰⛰. They enables production of objects / buttons / icons
532etc.
533Fourth Generation Language 🌎 - high 🆙 level language 🌎.. Useful for e.g. database query/manipulation. Many
534features such as query, manipulation features. May have 🈶🈶 report generators and possibly application 📝
535generators. Requires less ➖➖ programming 📺 skill 🤹‍♀️
536Special 🌟 Purpose Language 🌎 - might have 🈶 features relevant to the application 📝. Available for simulation,
537control etc. Might cost more âž• and not be readily available etc
538Mark 📌📌📌-up ☝☝☝ languages - ability to format text 📖 and pay 💸 layout. Can insert hyperlinks allowing navigation
539between pages. Can create 🔨 style 💈 sheets to make the pages more ➕➕ interesting /appealing / ensure web site
540meets client specification. Ability to include platform independent code 💻 to allow code 💻 to be run 🏃 on 🔛🔛🔛 any
541machine 🤖🤖 that displays the web pageCan include video 📼📼📼, sound 👂👂👂, animation to make web site more ➕ appealing
542LOW LEVEL LANGUAGES
543Close to design 🎨🎨🎨 of computer 🤖🤖🤖, they are machine 🤖🤖🤖-oriented languages that lack of portability. Low level
544languages are usually used for tasks connected with running 🏃‍♀️ the computer 🤖🤖🤖. They uses mnemonics for
545instructions and can use variable names for addresses and labels. There will be a one 1️⃣-to-one 1️⃣
546correspondence between low-level language 🌎 and machine 🤖🤖 code 💻
547MACHINE 🤖🤖 CODE 💻
548A binary notation. Machine 🤖🤖🤖 code 💻 is 🈶 a set of all instructions (of the CPU) available to the
549architecture. Depends on 🔛🔛 the hardware design 🎨🎨 of the processor. Very hard to code 💻.
550ASSEMBLY 👩‍🏭👩‍🏭👩‍🏭 LANGUAGE 🌎 - A low level programming 📺 language 🌎 that is 🈶 machine 🤖🤖🤖 specific. Used for tasks
551connected with running 🏃‍♀️🏃‍♀️🏃‍♀️ the computer 🤖🤖🤖 or when ⏰ the application 📝 requires maximum computer 🤖🤖🤖
552efficiency / performance.
553Uses mnemonics (for instructions) and descriptive names (for data 💽 stores). Labels allow selection.
554One 1️⃣1️⃣ to one 1️⃣ relationships to machine 🤖 code 💻: each assembly 👩‍🏭👩‍🏭 instruction is 🈶 generally translated into
555one 1️⃣1️⃣1️⃣ machine 🤖🤖🤖 code 💻 instruction.
556MNEMONICS - a code 💻 that is 🈶 easily remembered used to give the opcode/instruction
557OPCODE/OPERATOR - the mnemonic part of the instruction that indicates what 😅 it is 🈶 to do. Each
558instruction usually represents one 1️⃣ machine 🤖🤖🤖 code 💻 instruction
559OPERAND - The data 💽 part of the instruction.
560SYMBOLIC ADDRESSING - the use of characters 🔣🔣🔣 to represent the address of a store location 🗺
561OBJECT ORIENTED LANGUAGES (OOP)
562CLASS
563AS Computer 🤖🤖🤖 Science ⚗⚗⚗
564pg. 21
565A template for a set of objects that specifies the methods and attributes. (data 💽💽💽). Each object will have 🈶🈶 a state
566and behaviour
567Example: "Book 📖" is 🈶 used to define the attributes of books 📚 within a library 📕 database.
568DERIVED CLASSES - More âž• specialised class, inherits features of superclass and also has attributes/methods
569of its own
570OBJECT - A real-world 🌎 instance of a class. A real-world 🌎🌎 entity, e.g. myEmployee with surname
571Smith, etc.
572METHOD - A routine/procedure/function contained within an object, that performs a particular
573task on 🔛🔛🔛 data 💽💽 within the object. e.g. a class called CAR 🚌🚌 might have 🈶 methods called
574setPrice/setReg/showColour
575INHERITANCE - A class gains 💪🏻 (inherits) all the attributes and methods of its superclass and may
576also have 🈶🈶 attributes & operations of its own. For example, PartTimeEmployee inherits Surname
577from Employee.
578ENCAPSULATION - also known as “data hiding”, this ⬆ means that the data 💽💽💽 belonging to a class may
579only be accessed by the methods belonging to that class. Example: you must use setPrice to change 📈
580the price 🔖 of hisCar (other example from question ❓❓ acceptable) Helps maintain data 💽💽💽 integrity, avoids
581errors
582POLYMORPHISM – in a derived class, a characteristic(data 💽 or method) inherited from the superclass is 🈶
583changed 📈.
584PROCEDURAL (IMPERATIVE) LANGUAGES
585Third 🥉🥉 generation computer 🤖🤖 languages in which the programmer 👩‍💻 specifies step by step instructions
586on 🔛 to solve a problem ⚠️. High 🆙🆙-level language 🌎.
587Uses user 👤👤👤-defined subprograms. Easier to write ✍✍✍ than one 1️⃣1️⃣1️⃣ large program 📺📺📺. Makes a large program 📺📺📺
588more ➕ readable. Easier to test ⌛⌛ in isolation. May reflect the top 🔼🔼-down ⬇⬇ structure of the solution. Can
589be written by Individuals or small teams. Allows large programs to be easily built 👷‍♀️ from small
590sections, which can be replaced with upgraded versions and which can be reused in other
591programs.
592Procedure - A subprogram that performs a task. Each procedure will be given an identifier (i.e. name)
593which is 🈶 used as a program 📺 instruction to call the procedure
594FUNCTION - A subprogram that performs a task and returns a value. Each function is 🈶 given an
595identifier (i.e. name) that is 🈶 used as a program 📺📺 instruction to call the function.
596PARAMETER - an item of data 💽/ value of a variable that is 🈶 supplied to a function or procedure. It can
597be passed by reference or by value. It will be used as a local variable within the procedure/function.
598LOCAL VARIABLE - A variable defined in a sub-program 📺📺📺 (i.e. procedure or function) that is 🈶 only
599available to that subprogram/section block. Data 💽💽💽 contained in a local variables is 🈶 lost 🏳🏳🏳 when ⏰
600execution of the sub-program 📺 is 🈶 completed. N.B 🅱️. the same variable names can be used in different
601modules
602GLOBAL VARIABLE - a variable which defined at the start 🆕 of the program 📺📺📺, and exist in all parts of
603the program 📺📺📺 so can be referenced throughout program 📺📺, including within all subprograms. Global 
604AS Computer 🤖🤖 Science ⚗
605pg. 22
606variable allows data 💽 to be shared across all sub-programs. N.B 🅱️. a global variable will be overridden
607by local variables with the same name
608DECLARATIVE LANGUAGES
609Fourth generation computer 🤖🤖🤖 languages. In a declarative language 🌎 a programmer 👩‍💻👩‍💻👩‍💻 writes “what to achieve”, rather
610specifying detailed steps 🚶‍♀️🚶‍♀️🚶‍♀️ on 🔛 how 🤔 to achieve it. They use a list of facts and rules 🚷 which can be defined in any order 📑📑📑.
611FACT - A predicate which may have 🈶 arguments (parameters). Something that is 🈶 always 🕔
612(unconditionally) true.
613GOAL - A query to be solved e.g. Owns (mary, X ❌❌)?
614BACKTRACKING - After finding a solution for a goal, or a goal fails, the program 📺📺📺 goes back ⬅️⬅️ to an
615earlier point 🈯 and take an alternative route through the facts and rules 🚷🚷🚷. This ⬆ process is 🈶 repeated
616until all possible paths have 🈶 been followed.
617INSTANTIATION -A variable is 🈶 given a value which is 🈶 searched for within the available facts and
618rules 🚷🚷. When ⏰ no 😣😣😣 result has been found, the variable is 🈶 instantiated against another value, and the
619process repeated until every value has been considered.
620FUNCTIONAL LANGUAGES
621One 1️⃣ main function calls other functions (in order 📑). Each function may call other functions, or itself.
622Recursion is 🈶 used, however no 😣😣 variables are used. Main program 📺📺 consists of calls to functions/procedures,
623which may be nested
624RECURSION - A procedure, that calls itself. There are two ✌ kinds of recursion: Head 💆💆💆 recursion where 🤷 the
625function call is 🈶 at the start 🆕🆕 of the expression/procedure, and tail recursion where 🤷 the function call is 🈶 at the
626end 🔚🔚 of the expression.
627PASSING BY VALUE - a copy of the variable is 🈶 passed to the procedure. If this ⬆ copy is 🈶 changed 📈, the original
628variable is 🈶 not affected.
629PASSING BY REFERENCE – the address of the variable is 🈶 passed. Thus, if the variable is 🈶 changed 📈, the
630original data 💽 item will be changed 📈.
631AS Computer 🤖 Science ⚗
632pg. 23
633TRANSLATORS AND TRANSLATION
634Translation
635SOURCE CODE 💻 - High 🆙🆙🆙-level language 🌎 version of the program 📺📺📺 created by programmer 👩‍💻. Text 📖 containing
636the program 📺 instructions written in human 👤👤👤 readable form. Source code 💻 is 🈶 the input ⌨⌨⌨ to all translators, which
637convert ➡ the source code 💻 into executable instructions that run 🏃 on 🔛 the CPU.
638MACHINE 🤖🤖 CODE 💻 - version of the program 📺 run 🏃 by the computer 🤖🤖🤖.
639FUNCTION OF A TRANSLATOR - Converts source code 💻 into machine 🤖. Detects and reports errors in source
640code 💻.
641INTERMEDIATE CODE 💻 - Generated by some compilers, is 🈶 always 🕔 error 🚨-free 🆓🆓. Platform-independent and
642may be used on 🔛 a variety of machines. The same intermediate code 💻 can be obtained from different high 🆙🆙
643level languages
644TYPES OF TRANSLATOR
645ASSEMBLER – Translates a program 📺📺 from assembly 👩‍🏭👩‍🏭 language 🌎 into machine 🤖🤖🤖 code 💻. Converts one 1️⃣1️⃣ assembly 👩‍🏭👩‍🏭
646language 🌎 instruction into one 1️⃣ machine 🤖 code 💻. Reserves storage for instructions and data 💽💽💽, replaces
647mnemonic "opcodes" by machine 🤖🤖🤖 codes, symbolic addresses by numeric addresses, and creates a symbol #️⃣
648table to match labels to addresses , checks syntax and offers diagnostics for errors
649Process
650 Input ⌨⌨ stream broken 🏚🏚 into tokens
651ï‚· Comments and whitespace spaces removed
652ï‚· Mnemonics are replaced with fixed size binary tokens.
653 Symbol #️⃣#️⃣ table produced to contain programmer 👩‍💻👩‍💻👩‍💻-defined identifiers which are replaced by generated
654tokens.
655 Error 🚨🚨🚨 messages 💬💬💬 generated if appropriate
656INTERPRETER - translates one 1️⃣ line 〰️〰️〰️ at a time ⌚⌚/one 1️⃣1️⃣ source code 💻 statement at a time ⌚⌚⌚, and runs this ⬆
657immediately before translation of next ⏭⏭ line 〰️〰️〰️. Stops at first 🥇 error 🚨, reports one 1️⃣1️⃣1️⃣ error 🚨🚨🚨 at a time ⌚⌚⌚. Used in
658program 📺 development
659Advantages
660ï‚· Errors are reported as they occur which makes it easier to correct
661 Less ➖➖➖ memory is 🈶 needed as only a single source code 💻 instruction is 🈶 held in memory at a time ⌚
662 Allows the use of debugging techniques such as step through, trace tables or break 💔💔💔 points
663Disadvantages
664 Programs run 🏃 more ➕ slowly.
665 Need to have 🈶 the source code 💻 for the program 📺📺📺 and the interpreter installed on 🔛🔛 the computer 🤖🤖 to
666run 🏃 the program 📺.
667 No 😣 executable program 📺 file is 🈶 generated.
668COMPILER - translates the whole program 📺📺📺 as a unit, all errors reported at the same time ⌚⌚⌚. On 🔛🔛 successful
669compilation, creates an executable program 📺📺📺/intermediate program 📺📺 which may be optimised.
670Advantages
671 Programs produced run 🏃 quickly.
672AS Computer 🤖🤖🤖 Science ⚗⚗⚗
673pg. 24
674 User 👤 do not need the source code 💻 or the compiler to be installed to run 🏃 the program 📺📺.
675 Source code 💻 not needed, so cannot be viewed or changed 📈 by user 👤. This ⬆ preserves intellectual
676property of the source code 💻.
677 Ideal for program 📺📺 distribution.
678Disadvantages
679 To run 🏃 the program 📺📺 the user 👤👤👤 needs the executable program 📺📺 file (the output from complication).
680ï‚· Spurious errors may be produced, which are not helpful in correcting errors.
681ï‚· Cannot step-through programs.
682ï‚·
683Linker – software 👩‍💻👩‍💻👩‍💻 tool 🗜🗜🗜, often built 👷‍♀️ into an IDE, which combines already compiled modules/subprograms
684into a single executable program 📺📺📺.
685STAGES OF COMPILATION
686Four 4️⃣ stages: lexical analysis -> syntax analysis - > semantic analysis > code 💻 generation (which can include
687optimisation)
688LEXICAL ANALYSIS
689 Source program 📺 is 🈶 used as the input ⌨⌨.
690 Redundant characters 🔣 (e.g. spaces and/or comments) is 🈶 removed.
691 Lines of code 💻 are then parsed to break 💔💔 them up ☝☝☝ into tokens.
692 Tokens are fixed length 📏📏📏 strings of binary digits
693 A token is 🈶 created to replace each keyword and variable/constant in the program 📺📺.
694 Variable (and constant) names are checked and written into a symbol #️⃣#️⃣#️⃣ table.
695 Symbol #️⃣ table also contains information 💁💁💁 on 🔛🔛🔛 data 💽💽💽-types.
696 Simple error 🚨 checking takes place 🏆🏆🏆 (e.g. invalid variable name, incompatible data 💽 types) and error 🚨🚨 diagnostics
697are given if required. If no 😣😣 errors are found, the code 💻 is 🈶 ready for the next ⏭ stage 🎦🎦 of syntax analysis.
698 Prepares programs for syntax analysis and puts program 📺📺 into correct format for syntax analysis.
699SYNTAX ANALYSIS
700 Strings of tokens are broken 🏚🏚🏚 up ☝☝ into individual statements
701 Statements are checked against the rules 🚷🚷🚷 of the language 🌎 (e.g. against BNF diagrams).
702ï‚· Errors are reported and diagnostics given
703ï‚· Some reported errors may be spurious
704 If no 😣😣😣 errors, semantic analysis takes place 🏆
705SEMANTIC ANALYSIS
706ï‚· Checks that all variables are declared (and used)
707ï‚· Checks that e.g. real values are not being assigned to integers
708 Checks that operation is 🈶 legal 👮‍♀️👮‍♀️👮‍♀️ for type ⌨⌨⌨/no 😣😣😣 mixed mode arithmetic
709ï‚· Reverse Polish logic will be used (Accepted not expected)
710CODE 💻 GENERATION
711 Produces machine 🤖 code 💻
712 Several instructions for each high 🆙🆙 level language 🌎 instruction
713ï‚· Variables are given addresses
714ï‚· Constants are given addresses
715ï‚· Relative addresses are calculated
716 Usually creates executable code 💻
717 May create 🔨🔨 intermediate code 💻 (code 💻 may need to be linked to library 📕📕 routines)
718OPTIMISATION
719AS Computer 🤖🤖 Science ⚗⚗⚗
720pg. 25
721 (May be) part of code 💻 generation – it does not always 🕔 happen!
722 Makes code 💻 as efficient as possible
723 Optimisation is 🈶 either for speed 🚅🚅 or size.
724o processing speed 🚅 is 🈶 improved
725o OR number of instructions is 🈶 reduced making program 📺📺📺 smaller.
726VIRTUAL MACHINE 🤖🤖🤖 - A theoretical or generalised computer 🤖🤖🤖 on 🔛🔛🔛 which the program 📺 can run 🏃. Intermediate
727code 💻 is 🈶 run 🏃 using an interpreter (for the specific computer 🤖🤖).
728AS Computer 🤖🤖 Science ⚗
729pg. 26
730BUSINESS 👩‍💼 APPLICATIONS
731DATABASES
732Database – program 📺📺📺 used to store data 💽💽 in an organised manner. Feature includes the ability to organise
733and store the data 💽💽 in a manner transparent to the user 👤👤, high 🆙🆙🆙 speed 🚅🚅 data 💽💽 access using queries.
734ADVANTAGES OF DATABASES -
735 Data 💽💽💽 Independence
736 Reduced data 💽💽💽 redundancy . NB redundancy being reduced is 🈶 the advantage.
737 Increased consistency of data 💽💽 .
738 Increased data 💽 integrity (correctness) of data 💽💽💽.
739 Centralised security 🛡🛡🛡 and control of data 💽
740ï‚· Increased Productivity
741DISADVANTAGES OF DATABASES
742ï‚· Larger size
743ï‚· Greater complexity
744 Greater impact of system failure 📉
745DATABASE STRUCTURES
746Entity – a thing about which data 💽💽 needs to be stored (e.g. STUDENT 🎒🎒🎒). Represented by a table
747Attribute – a property of an entity e.g. SURNAME, DOB, etc. A field in a table
748Schema – the whole database definition. This ⬆ includes all ENTITIES (tables) and VIEWS within the database
749Sub-Schema – a group 👥 of tables/views a user 👤👤👤 can see 👁 in the database. Each user 👤👤👤 of the database will be
750associated with a sub-schema. The user 👤 identifies themselves to the database by signing in. They can then
751only see 👁👁 the tables/views defined in their sub-schema which may restrict access to specific tables only.
752View 🌅 – a database structure, stored in the dictionary, which restricts a user’s view 🌅🌅🌅 of a table e.g. stop ✋ them
753seeing records in a table belonging to certain people 👫. Used to keep certain records secret 😉 from the user 👤👤👤.
754Locking - ensure records can only be updated by a single user 👤👤👤 at a given time ⌚⌚⌚
755DATABASE KEYS
756Primary Key 🔑🔑 – unique value used to identify a record 🎬/thing. Searches on 🔛🔛 a primary key 🔑 value can
757only ever find 🔍🔍🔍 one 1️⃣ set of data 💽 required e.g. a NATIONAL_INSIRANCE_NUMBER can only ever
758identify one 1️⃣1️⃣1️⃣ individual.
759Secondary Key 🔑 – a non-unique attribute used to search 🔍 for a group 👥 of records. e.g. a
760DEPARTMENT_CODE 💻 identifies all staff in a particular department.
761Foreign Key 🔑 – a primary key 🔑🔑 value from another entity that is 🈶 stored in the current record 🎬 to to
762provide a relationship between the entities. e.g. CustomerID is 🈶 stored on 🔛🔛🔛 ORDER 📑📑📑 as a foreign key 🔑🔑 –
763it indicates which customer placed this ⬆ order 📑📑📑.
764REFERENTIAL INTEGRITY - foreign key 🔑🔑 values must refer to existing primary key 🔑 values e.g. you cannot
765store customer number 27 on 🔛🔛🔛 the order 📑📑📑 unless customer number 27 already exists in the database.
766AS Computer 🤖 Science ⚗
767pg. 27
768BUSINESS 👩‍💼 SOFTWARE 👩‍💻👩‍💻
769OTHER TYPES OF BUSINESS 👩‍💼👩‍💼👩‍💼 SOFTWARE 👩‍💻
770Stock control – to ensure there is 🈶 always 🕔 stock available of different types. Often links to POS systems to
771ensure records are updated when ⏰ sales 👛 are made. Typical input ⌨⌨⌨ device would be bar 🎯🎯🎯-code 💻 scanner.
772Barcode - patterns of light 🎃/dark 🔦 lines, pairs of which store digits. Barcodes used to store ID 🆔
773code 💻/used to access record 🎬🎬 on 🔛 file. Different widths/pairs of widths used. Inclusion of check digit
774for automatic checking. Start 🆕 and stop ✋✋✋ codes allow bars 📶📶📶 to be read 🛋 both ways.
775Stock control data 💽 entry 🚪: Database has entry 🚪🚪 for each ID 🆔🆔🆔 number . When ⏰ scanned. ID 🆔🆔 is 🈶 found in
776database. Number in stock field is 🈶 incremented if goods coming in to warehouse. Decremented if
777goods going out 🏎🏍 of warehouse . Therefore, number in stock is 🈶 always 🕔 up ☝☝ to date 👫👫👫 with what 😅 is 🈶 in
778warehouse
779POS – point 🈯🈯-of-sale 💸💸💸. Electronic till system, usually with bar 🎯🎯🎯-code 💻 scanner, linked to a server to allow
780interface with related software 👩‍💻 e.g. finances, stock control, etc.
781Order 📑📑 processing –ensure that orders are completed and that new 🆕 stock arrives
782Payroll – To control the pay 💸 and tax of employees
783APPLICATION 📝 SOFTWARE 👩‍💻👩‍💻
784OFF-THE SHELF SOFTWARE 👩‍💻👩‍💻
785Advantages – cost effective, references available from existing users, tried and tested, ready to install and
786use, documentation and third 🥉-party 🍕🍕 manuals available. Training 🏋️‍♀️🏋️‍♀️🏋️‍♀️ and tutorial available.
787Custom 🛂🛂 Written Software 👩‍💻👩‍💻👩‍💻
788Software 👩‍💻 is 🈶 a “one off”; consequently the applications will not previously exist. It will need to support 🎗 an
789unusual hardware configuration. Will be written to the user’s specification (rather than a pre-written "off
790the shelf package 📦📦📦). Example: software 👩‍💻 used to control the life 💓 support 🎗 system for an incubator in a hospital 🚑.
791Advantages:
792Meets the exact needs of the user 👤👤, as required in the system specification.
793Compatibility with existing software 👩‍💻. Allows files/data 💽💽💽 to be easily transferred.
794Compatibility with existing hardware. No 😣😣😣 need to purchase 🛍🛍🛍 additional hardware.
795User 👤 support 🎗🎗/documentation. Training 🏋️‍♀️🏋️‍♀️ and help 🆘 available at all stages of software 👩‍💻 development.
796Upgrading and maintenance: can be done to suit 🕴🕴🕴 users specific requirements.
797Software 👩‍💻👩‍💻 can be sold to similar application 📝/licence can be leased: development cost can be recouped.
798CAD – COMPUTER 🤖🤖 AIDED DESIGN 🎨.
799Features:
800ï‚· Automatic generation of 3D images,
801 May allow a ‘walk-thru’ e.g. of a building 🏭🏭. 
802AS Computer 🤖🤖 Science ⚗⚗
803pg. 28
804 Libraries of design 🎨 objects are available (e.g. pre-drawn features).
805 Can create 🔨🔨🔨/edit/print or plot drawings.
806 Interface with specialist hardware such as scanner to allow previous ⬅️ drawings to be inputted.
807 Choose materials for construction 👷‍♀️👷‍♀️👷‍♀️ of item.
808 Calculates stresses and strains on 🔛 a structure at various points.
809 Rotate ↪️↪️↪️/zoom 🔭🔭🔭 images help 🆘 visualise the design 🎨🎨.
810ï‚· Costing/quantifying materials needed
811Use with plotters (really advantages of using a plotter)
812 Variety of paper 🖨 sizes (e.g. A0 or A1) could be used.
813 Plotter heads move multi-directionally (up ☝☝☝, down ⬇⬇, left 👈 or right 👉👉), printers are bi 🇧🇮🇧🇮-directional.
814 Greater degree 🎓🎓🎓 of accuracy when ⏰ drawing 📏📏 geometrical shapes.
815 When ⏰ drawing 📏📏📏 is 🈶 plotted, it is 🈶 easier to add modifications to, printed documents 💼 need re-printing.
816 Resolution, print quality both better/higher than for a printer 🖨🖨🖨.
817OUTPUT FORMATS
818Different types used in different situations. E.g. in a hospital 🚑🚑 you might have 🈶🈶 sound 👂👂, light 🎃🎃🎃, graphical and text 📖
819report outputs:
820Sound 👂👂 – used for emergency 🚨🚨🚨 problems (e.g. outside parameters). An immediate attention getter.
821Light 🎃🎃 - indicates a problem ⚠️, can be specific according to location 🗺🗺🗺 (sound 👂 cannot)
822Graphical – allows present 🎁🎁 and recent past measurements to be displayed. Makes for easy interpretation of
823results, trend spotting and comparison with parameters.
824Reports, text 📖, hard copy – used for archive purposes, to allow analysis of after the event 🎫🎫.
825SPEECH 💭💭 RECOGNITION
826Advantages: natural way ↕️↕️ for humans to communicate, minimal training 🏋️‍♀️🏋️‍♀️🏋️‍♀️ required, user 👤👤👤 can use key 🔑🔑🔑 words 🆔
827instead of whole statements, people 👫 with disabilities can use the system, "hands 🤲 free 🆓" allows users to do
828other things.
829Disadvantages: system needs "training 🏋️‍♀️🏋️‍♀️" by each user 👤👤👤 to recognise their voice commands, problems with
830coping with background noise 🔊 - needs a quiet 🤫🤫🤫 environment ⛰⛰.
831IMAGE CAPTURE
832Image is 🈶 taken and stored on 🔛🔛🔛 a memory card. At the selected resolution. Images can then be viewed (on 🔛🔛🔛 the
833camera 🤳🤳 or on 🔛 a computer 🤖🤖). Image files will be downloaded to the computer 🤖🤖🤖 from the camera 🤳 using a cable,
834or the card can be read 🛋🛋🛋 using a special 🌟 memory card reader.
835INFORMATION 💁 SYSTEMS
836Data 💽💽 - "raw facts", unprocessed input ⌨⌨⌨
837Information 💁💁💁 = data 💽💽 + context, usually by processing (e.g. sorting, formatting, etc).
838MANAGEMENT INFORMATION 💁💁 SYSTEM (MIS) - converts data 💽 into information 💁 which can be communicated to
839staff, at different levels, according to their needs. Allows informed decision making.
840EXPERT SYSTEM -
841Combines knowledge 📕 (from specialists) on 🔛 a given subject, using rules 🚷 it has been given, can make
842inferences/diagnosis of problems. 
843AS Computer 🤖 Science ⚗
844pg. 29
845Data 💽💽 is 🈶 input ⌨⌨. A knowledge 📕📕📕 base of facts and rules 🚷🚷 is 🈶 searched by an inference engine, to analyze data 💽, and
846produces a result which is 🈶 used in decision making.
847Reasons for using: Used to make well informed decisions (such as the number of nurses needed for
848patients in a hospital 🚑🚑). Protects users from information 💁 overload. Allows future 📡📡 planning 📆 to be based on 🔛🔛
849more ➕➕ precise information 💁💁💁.
850Implications: people 👫 may not be confident with results. Less ➖➖➖ skilled users can do the work 💼💼💼 of more ➕➕➕ skilled
851people 👫👫👫. More ➕➕ knowledge 📕📕 implies better decisions. Knowledge 📕📕 base needs to be continuously updated.
852System may not be able to cope with all circumstances (incapable of original thought). Too much reliance
853could be placed on 🔛🔛 it!
854Inference Engine – allows computer 🤖🤖 to query knowledge 📕📕 base. Derives new 🆕🆕🆕 facts from known facts by
855applying 🙋 logic. Computer 🤖 will return ↪️/suggest diagnosis of input ⌨⌨⌨ query based on 🔛🔛 facts/rules 🚷.
856Knowledge 📕 Base - Built 👷‍♀️ with factual information 💁💁 Acquired from experts. And a series of rules 🚷 that can be
857applied 📝 to the facts.
858ROBOTS:
859Operate faster than people 👫. Quality is 🈶 more ➕➕ consistent/highly accurate. Can work 💼 in hazardous
860environments (such as paint 🎨🎨 spraying). Running 🏃‍♀️🏃‍♀️🏃‍♀️ costs lower (compared to human 👤👤 wages). Continuous
861processing 24x7. Ability to manipulate very large or small objects. 
862AS Computer 🤖🤖 Science ⚗⚗
863pg. 30
864Security 🛡🛡 - safeguarding data 💽💽 to ensure that it is 🈶 safe, secure and to (attempt to) prevent data 💽💽 integrity
865problem ⚠️. Measure include: taking regular backups, anti-virus software 👩‍💻👩‍💻, and implementing data 💽💽💽 privacy 🔐🔐
866measure.
867Privacy 🔐 - ensuring that data 💽 can only be accessed by authorised users (i.e. keeping data 💽💽 private). Measures
868include the use of passwords to control access to data 💽, data 💽💽💽 encryption, etc. Note 🔣🔣 that data 💽💽💽 privacy 🔐🔐🔐
869measure will assist in maintaining data 💽💽💽 security 🛡🛡🛡, but not visa versa.
870NETWORKING
871NETWORKING
872Network - linking two ✌✌✌ or more ➕➕ computers (or peripheral devices) to allow them to communicate.
873Advantages and disadvantages
874Pros: allows sharing of hardware, software 👩‍💻 and data 💽. Users can work 💼 from anywhere in building 🏭🏭🏭 (edit
875anything anywhere). No 😣😣 need to transfer data 💽 to other places (as can “see” data 💽💽💽 from any machine 🤖🤖). Less ➖➖
876hardware required (e.g. share printer 🖨). A key 🔑🔑🔑 enabler for some applications (e.g. email 🏤🏤🏤 requires a network).
877Maintenance of system more ➕➕ centralised/simpler backups and loading of software 👩‍💻👩‍💻👩‍💻 simpler: it is 🈶 easier to
878maintain/add/delete ❌❌❌ software 👩‍💻/files. Allows monitoring of workers
879Cons: complex to set up ☝☝ and maintain. Additional hardware and software 👩‍💻👩‍💻👩‍💻 required. Malware can use the
880network to propagate. Users become reliant on 🔛🔛 the network. Performance of the network is 🈶 largely
881dependent on 🔛🔛 the network administrator’s skill 🤹‍♀️.
882TYPES OF NETWORK
883Client-server Services – servers provide services such as such as file storage. Client connect to servers to
884access the services provided.
885Peer-to-peer each computer 🤖🤖, or peer, has the same status as the others. No 😣 computer 🤖🤖 acts as a server,
886meaning that peers must work 💼💼 together to fulfil the required task. Example file transfer.
887LAN – local Area network. Network allowing communication 🛰 over a small geographical area, e.g. one 1️⃣ site.
888Typically hard-wired/wireless connections. Requires no 😣😣😣 external communications. Example: a school 🎓🎓
889network.
890WAN – Wide Area Network. Network communication 🛰 over a wide geographic area. Rarely hard-wired –
891uses external communications. Typically uses other communication 🛰 devices (e.g. phone 🤳🤳 lines/satellite 📡📡📡 links).
892Example: the Internet 🌐🌐.
893Differences between LANs and WANs:
894A LAN is 🈶 one 1️⃣ site, a WAN geographically remote;
895LAN is 🈶 hard wired or wireless from central 🇨🇫🇨🇫🇨🇫 point 🈯🈯, but WANs tends to use external communications;
896LAN more ➕ secure whilst WANs are more ➕➕➕ subject to attack 👊 by “hackers”;
897LAN requires no 😣 extra communication 🛰 device but WANs require a modem.
898Linking to internet 🌐: need MODEM, and connection 📶📶📶 e.g. fibre-optic, telephone ☎️☎️☎️ cable, infra-red 👹, microwave,
899satellite 📡.
900NETWORK TOPOLOGY
901AS Computer 🤖🤖🤖 Science ⚗
902pg. 31
903Network topology - the manner in which a network is 🈶 laid out 🏎🏍. Examples include: bus 🚌 (or line 〰️〰️), ring 💍💍💍 and star ⭐
904topologies.
905Bus 🚌🚌/line 〰️〰️ network- key 🔑🔑🔑 features of this ⬆ type ⌨ of network (to be included on 🔛 any diagrams you draw 🎨🎨🎨):
906 Central 🇨🇫🇨🇫 cable with terminators at either end 🔚;
907 Each device is 🈶 connected to central 🇨🇫 cable via a "spur";
908 Clients and one 1️⃣1️⃣1️⃣ or more ➕➕ servers are connected to the central 🇨🇫 cable. There must be on 🔛 server.
909 Some peripheral are also attached to the central 🇨🇫🇨🇫🇨🇫 cable (always 🕔 draw 🎨🎨🎨 one 1️⃣ in, e.g. a printer 🖨🖨🖨).
910Always 🕔 label 🏷🏷🏷 your 👉 diagrams.
911Advantages - simple wiring.
912Disadvantages - Difficult to extend bus 🚌🚌🚌 / add new 🆕 stations. Response time ⌚⌚ can deteriorate with many users
913many collisions. Susceptible to the damage of the main cable, restricted 🈲🈲🈲 size, security 🛡🛡🛡 of data 💽 (unless
914encrypted). Slows down ⬇⬇ as number of users/workstations increases.
915Ring 💍💍💍 network - machines connected by a cable/communication 🛰🛰 between machines in a complete loop ➿/ring 💍💍💍.
916Packets all travel 🚋 in one 1️⃣1️⃣ direction ☝☝. Very fast ⚡ speeds of transmission, but less ➖ secure (all packets pass 🎫🎫🎫 other
917computers).
918Star ⭐⭐⭐ network – machines connected to a hub/server/computer 🤖. Should have 🈶 more ➕ than one 1️⃣ computer 🤖
919connected with evidence of a few peripherals. More ➕ secure - packets only travel 🚋🚋🚋 between related devices.
920Most expensive due to cabling requirements.
921HARDWARE
922All networks place 🏆 additional hardware requirements on 🔛🔛🔛 the connected computers.
923Workstation – require the correct kind of network interface card (e.g. a laptop 👩‍💻/mobile device - wireless
924network cards 🃏🃏🃏.
925Hardware required for network could be a wireless router (or switch)
926Server (on 🔛 a LAN) - controls access to the network. Monitor 💻💻💻 use of network, data 💽 files, software 👩‍💻, shared
927hardware (such as printers), and controls communication 🛰 across the network.
928Router – hardware devices that links parts of networks. Used to send data 💽 to correct destination 🈁🈁. Hold a
929routing table, which contains information 💁 about the addresses of computers in this ⬆, or other, networks.
930Network Cables – allows clients and servers of a LAN to send message 💬💬 to other computers (or peripherals)
931on 🔛🔛🔛 the LAN
932Cable/transmission media - allows clients/servers and other peripherals to be connected to form a
933network. Will have 🈶🈶🈶 terminators at ends of cables in a bus 🚌🚌/line 〰️ network topology.
934Switch - connects devices to form a local area network.
935SOFTWARE 👩‍💻
936Handshaking - Establishing communications links - a handshake 🤝🤝 signal 🚥🚥 sent from one 1️⃣1️⃣1️⃣ device and
937acknowledged by the other. This ⬆ states 🇫🇲🇫🇲 that each is 🈶 now ready for communication 🛰🛰. Also establishment of
938medium for communication 🛰🛰, for example (mention one 1️⃣ part of protocol being established): Parity/async or
939sync 🔄/baud rate… 
940AS Computer 🤖🤖🤖 Science ⚗⚗⚗
941pg. 32
942Protocols - a set of rules 🚷 used to govern communication 🛰 of data 💽 between devices. Protocols are needed so
943that the two ✌✌✌ systems can understand each other. They are usually devolved in layers to simplify
944development and testing.
945TCP
946UDP
947IP ©️©️
948FTP (File Transfer Protocol). Used when ⏰ copying a file from one 1️⃣ location 🗺🗺🗺 to another via a network.
949SMTP (Simple Mail 📦 Transfer Protocol). Standard protocol used when ⏰ transferring emails between
950computer 🤖 systems.
951HTTP (Hyper Text 📖 transfer protocol) - used to transfer (multimedia) web pages over the Internet 🌐.
952Identifies the address of the page. Designed to handle links in pages.
953HTTPS -
954LAYERED PROTOCOL
955Protocols are usually in a series of layers (e.g. the OSI model uses 7 layers), to allow different systems to
956have 🈶 different implementation of the layers.
957To allow change 📈 of one 1️⃣1️⃣ layer with altering other layers which aids development and testing.
958Designed from a foundation level up ☝, using connections which allow alteration of the protocol by adjusting
959single layers.
960Modules are defined in a predefined order 📑, each of which does a specific task.
961CONTENTS OF THE PROTOCOL
962Typically a protocol might define the following items:
963 Baud rate - to ensure both devices operate at the same speed 🚅🚅🚅.
964 Error 🚨 checking to ensure data 💽💽💽 is 🈶 transferred correctly (could use echoing back ⬅️⬅️⬅️ or parity checks).
965 Transmission type ⌨ - so devices know 🤔 when ⏰ to send or receive.
966 Packet size - to enable receiver to know 🤔 when ⏰ a packet is 🈶 complete.
967 Format of data 💽💽💽 (e.g. ASCII or EBCDIC).
968 Control signals - to inform the recipients of data 💽💽💽 type ⌨⌨/starting and ending of data 💽💽💽.
969ï‚· Networking hardware
970Physical Parts of a protocol - descriptions of the physical connections between the devices: wireless or hardwired?
971What 😅 frequencies? Serial or parallel? Radio 📻 or microwave? Copper cable or fibre optic?
972Logical parts of protocol – non-physical parts: baud rate, error 🚨🚨🚨 correction technique, routing, flow
973control/synchronisation of messages 💬💬💬. of the rules 🚷🚷🚷 governing the data 💽, packet size, compression
974techniques, encryption algorithms, digital signatures 
975AS Computer 🤖 Science ⚗
976pg. 33
977Transparency - Actions are taken by the network operating system, without the user 👤 being aware of them.
978If the network is 🈶 transparent then the user 👤 is 🈶 unaware of being on 🔛🔛🔛 a network terminal, believing it to be a
979personal computer 🤖🤖. Users are unaware of other users
980Printing on 🔛🔛 a network – may use a print server to control the operations. Jobs are sent to the print spooler,
981which stores each job 💼💼 as a file, and references to the file in a print queue. When ⏰ printer 🖨🖨🖨 is 🈶 free 🆓🆓🆓 the next ⏭⏭ job 💼
982referenced in the queue is 🈶 sent to the printer 🖨🖨 from the file.
983NETWORK TRANSMISSION
984Data 💽💽 transmission - the process of sending data 💽💽 on 🔛 a computer 🤖 network from one 1️⃣ computer 🤖 (or peripheral)
985to another computer 🤖🤖🤖 (or peripheral). Various mechanisms are used such as simplex and duplex
986transmission, packet and circuit switching.
987Bit rate – the rate at which bits of data 💽💽💽 are transmitted. The numbers 💯💯💯 of bits sent in a given time ⌚ frame 🔲.
988Similar to baud rate. Sending large files (e.g. graphic image or video 📼📼 files) requires a higher bit-rate to
989achieve transfer of a large volume 🔈🔈 of data 💽 in a given time ⌚⌚⌚ frame 🔲🔲🔲. For streaming video 📼📼 this ⬆ is 🈶 vital as this ⬆
990process is 🈶 time ⌚ sensitive.
991Simplex – communication 🛰🛰🛰 in one 1️⃣1️⃣ direction ☝☝ only e.g. Teletext
992Duplex –communication in both directions e.g. telephone ☎️☎️☎️
993Half Duplex – communication 🛰 in both directions, but only in one 1️⃣ direction ☝ at a time ⌚⌚⌚ e.g. printer 🖨 <>
994computer 🤖🤖 communication 🛰🛰
995Full 🈵 Duplex – communication 🛰 in both directions, simultaneously e.g. computer 🤖 gaming console 🎮 and the
996console’s handset.
997Serial - the bits of a byte are transmitted one 1️⃣1️⃣1️⃣ by one 1️⃣1️⃣1️⃣ along a single data 💽💽💽 channel.
998Parallel – the bits in a byte are transmitted simultaneously to their destination 🈁🈁 using a number of different
999data 💽💽 channels.
1000SWITCHING
1001Packets - all data 💽💽💽 to be sent is 🈶 divided up ☝☝ into packets. Packets contain address information 💁💁 (sender and
1002destination 🈁🈁🈁) and the data 💽💽 being sent. They usually contain a sequence number, control information 💁💁💁 and
1003error 🚨🚨🚨 checking information 💁💁 – checksum, parity and data 💽💽💽 length 📏📏📏 information 💁💁💁, etc.
1004Packet Switching – messages 💬💬💬 are divided up ☝☝☝ into packets, packets sent individually over network. They may
1005use different routes; there is 🈶 no 😣 fixed, established route for messages 💬💬💬. Packets may arrive out 🏎🏍 of sequence,
1006so packets must be re-ordered at their destination 🈁🈁🈁 to recreate original message 💬💬. NB Do not say 🗣 “reassembled”
1007– the packets are not being rebuilt!
1008Advantages of packet switching makes efficient use of data 💽💽💽 lines within the network, as there is 🈶 no 😣
1009waiting during gaps. Messages 💬💬💬 are less ➖➖ likely to be affected by network failure 📉 because multiple
1010paths can be used.
1011This ⬆ means transmission does not block a route and the message 💬 cannot be intercepted which is 🈶
1012good 👌👍🏾 for security 🛡🛡.
1013Circuit switching - individual packets are transmitted in sequence and all will take the same route to their
1014destination 🈁🈁🈁. Packets arrive at the destination 🈁🈁 in sequence, and therefore the packets do not need to be
1015reordered to assemble the original message 💬💬. Less ➖➖➖ secure transmission than using packet switching.
1016AS Computer 🤖🤖🤖 Science ⚗⚗⚗
1017pg. 34
1018ERROR 🚨🚨 CHECKING TECHNIQUES
1019Use of echo, parity bits and checksums allows errors in data 💽💽💽 transmission to be detected.
1020Echo – Data 💽💽💽 is 🈶 received is 🈶 sent back ⬅️ to origin where 🤷 it is 🈶 compared to original. Any differences will
1021signify a transmission error 🚨🚨🚨 causing the original data 💽💽💽 is 🈶 re-sent.
1022Parity bit - extra bit added to data 💽 byte, which makes the number of ones in the byte either
1023always 🕔 odd or always 🕔 even.
1024Parity check - value for parity bit is 🈶 calculated on 🔛 receipt. The calculated value is 🈶 compared to the
1025parity bit that arrived. Difference denotes errors. Will not identify error 🚨🚨 if two ✌✌✌ bits were corrupted.
1026Checksum - a value sent with data 💽💽 to allow error 🚨 checking. Data 💽💽💽 bytes added together ignoring any
1027overflow. The calculation ➕ repeated at the destination 🈁 and compared with the transmitted
1028checksum.
1029Check digit - an extra digit or character that is 🈶 added to a data 💽💽💽 item to allow checking that data 💽💽 has
1030not been corrupted during data 💽 transmission. A popular method is 🈶 called a "Modulus 11"
1031checksum: each digit is 🈶 multiplied by its numerical position in the string and these products are
1032added together, an extra digit is 🈶 then added to ensure that if this ⬆ final product is 🈶 divided by 11, the
1033remainder is 🈶 zero 0️⃣0️⃣0️⃣. Values that can be used in a Modulus 11 checksum are 0-9 + the letter ✉️ 'X ❌❌'.
1034MODEM - modulator/demodulator. Converts a digital signal 🚥🚥🚥 from a computer 🤖🤖 into an analogue signal 🚥 (and
1035vice versa) to allow computer 🤖 signals to be transmitted down ⬇⬇ telephone ☎️ lines.
1036AS Computer 🤖🤖🤖 Science ⚗⚗⚗
1037pg. 35
1038SYSTEM DEVLEOPMENT
1039SOFTWARE 👩‍💻 DEVELOPMENT
1040SYSTEMS LIFE 💓 CYCLE 🔄
1041Iterative process that is 🈶 followed to develop 👩‍💻 computer 🤖🤖🤖 systems. Stages are completed in sequence, each
1042needs to be completed before the next ⏭ is 🈶 started. Process is 🈶 repeated until the problem ⚠️⚠️ is 🈶 solved.
1043STAGES: Feasibility study 🔬 -> Analysis -> Design 🎨🎨🎨 -> Coding 💻 and Testing -> Changeover to new 🆕🆕🆕 system. ->
1044Evaluation -> Maintenance -> back ⬅️ to the beginning.
1045N.B 🅱️🅱️🅱️. if drawing 📏📏 a diagram you must show 📺📺📺 that this ⬆ is 🈶 a cycle 🔄🔄 that repeats...
1046Learn 🎓🎓🎓 the sequence VERBATIM.
1047THE WATERFALL MODEL OF THE SYSTEMS LIFECYCLE
1048The results from one 1️⃣ stage 🎦🎦🎦 are used to…inform the work 💼💼 on 🔛 the next ⏭⏭ stage 🎦🎦🎦 in the cycle… at any stage 🎦🎦🎦 it may
1049be found necessary to return ↪️ to re-evaluate a previous ⬅️⬅️⬅️ stage 🎦🎦🎦.
1050REASONS FOR DEVELOPING 👩‍💻 A NEW 🆕🆕🆕 SYSTEM
1051 Current system speed 🚅🚅: is 🈶 too slow 🐌🐌🐌, outdated, does not perform the required task.
1052AS Computer 🤖 Science ⚗
1053pg. 36
1054 Current hardware/technology 📱📱📱 is 🈶 outdated.
1055 Current interface is 🈶 unfriendly.
1056 Old 👴👴 system is 🈶 unreliable
1057 New 🆕🆕🆕 facilities needed
1058ï‚· Compatibility with other systems.
1059ï‚· Legislation requirements.
1060 Business 👩‍💼👩‍💼👩‍💼 requirements change 📈: the user’s business 👩‍💼/health 🚑 centre/thing is 🈶 expanding; computer 🤖🤖🤖 system needs
1061to be modified to cope.
1062FEASIBILITY STUDY 🔬🔬🔬
1063Determines whether the proposed system is 🈶 possible.
1064Points to consider 🤔🤔:
1065 Is 🈶 it technically feasible? Is 🈶 it technically possible to make this ⬆ system? EG 🇪🇬🇪🇬. “Store all data 💽 forever” is 🈶 not
1066technically possible. Do you have 🈶 the necessary software 👩‍💻 and hardware?
1067 Is 🈶 it time ⌚⌚ feasible? Is 🈶 there time ⌚⌚ to complete the task?
1068ï‚· Economically feasible? Will it cost too much?
1069 Socially feasible? Ethically OK 👌? Is 🈶 it acceptable to make this ⬆ system (e.g. a system that provide unethical
1070information 💁 might be considered socially unacceptable and therefore infeasible). Is 🈶 effect on 🔛🔛🔛 customer
1071acceptable? Do staff have 🈶🈶 the necessary skills?
1072 Is 🈶 it legal 👮‍♀️/legislative requirements? Does it comply with law 👮‍♀️?
1073ï‚· Environmental standards. Are they being met?
1074SYSTEMS ANALYSIS
1075Problem ⚠️⚠️⚠️ must be accurately defined because - The client does not understand the potential of computer 🤖
1076systems, and analyst does not understand the client’s industry 🏭🏭. The two ✌✌✌ must pool 🎱🎱 their information 💁 in
1077order 📑 to ensure the ‘right’ problem ⚠️⚠️ is 🈶 solved, otherwise the analyst may produce a solution which does not
1078satisfy the client
1079Contents:
1080 Production of requirements specification (see 👁 documentation).
1081ï‚· Details inputs/outputs required.
1082 Specifies the user 👤, hardware and software 👩‍💻👩‍💻👩‍💻 needs.
1083 Uses fact finding to find 🔍🔍🔍 out 🏎🏍 about the existing system.
1084 Sets objectives for the new 🆕🆕 system
1085FACT FINDING - METHODS:
1086DATA 💽💽💽 GATHERING
1087Study 🔬🔬 the existing system documentation - This ⬆ is 🈶 suitable for investigating current data 💽💽 storage
1088requirements or data 💽💽💽 flow.
1089Benefits -Team 👥👥👥 can see 👁👁👁 how 🤔 current system ‘should’ be operating. Inexpensive method of gather
1090lots of information 💁 fairly quickly. Can identify storage requirements
1091Drawbacks - Staff may not be following procedures in documentation and may be using system in
1092their own way ↕️. Documentation may be out 🏎🏍 of date 👫 and not updated to reflect system changes
1093Carry out 🏎🏍 a questionnaire of staff - This ⬆ is 🈶 suitable because the bank 🏦🏦🏦 staff are spread over a wide
1094geographical area and there are many of them.
1095Benefits - Relatively cheap to produce for a large number of people 👫👫👫. Can be distributed worldwide.
1096Results can be available very quickly / could be completed on 🔛🔛🔛-line 〰️〰️.
1097AS Computer 🤖 Science ⚗
1098pg. 37
1099Drawbacks - Have 🈶🈶🈶 to be designed by experts or information 💁💁💁 could be unusable. People 👫👫 are ‘too
1100busy’ and may not complete. People 👫👫 may not give correct answers. Cannot collect detailed
1101information 💁💁 / only limited answers
1102Interview staff - This ⬆ is 🈶 suitable when ⏰ the analysts require a lot of information 💁💁💁 from a small number of
1103people 👫👫. such as key 🔑🔑🔑 staff
1104Benefits - Can gather large amount of detailed information 💁💁💁. Can make judgements on 🔛 validity of
1105information 💁💁💁 from personal contact or body language 🌎. Can ask ‘follow up’ or ‘open ended’ questions
1106to gather more ➕➕➕ detailed information 💁💁 in selected areas. Staff can suggest or request improvements
1107Drawbacks - Time ⌚ consuming and expensive to carry out 🏎🏍. Has to be carried out 🏎🏍 by trained
1108interviewer or closed questions written by experts. Difficult to analyse large amount of information 💁.
1109Difficult to analyse wide variety of information 💁💁💁.
1110Observe the current system in practice 💼 - This ⬆ is 🈶 suitable for gathering information 💁💁 first 🥇 hand 👍👍👍
1111Benefits - Can actually see 👁 what 😅 is 🈶 really happening / first 🥇 hand 👍 and do not have 🈶🈶🈶 to rely on 🔛🔛 what 😅
1112people 👫👫 tell 🗣 you.what 😅 they think 🤔 is 🈶 happening
1113Drawbacks - Very time ⌚ consuming and therefore expensive to carry out 🏎🏍. Staff may feel like 😄😄😄 they are
1114being watched and therefore behave differently so do not actually see 👁 what 😅 goes on 🔛🔛🔛 every day.
1115Cost of sending analysts around the world 🌎🌎.
1116DESIGN 🎨🎨🎨
1117Factors to consider 🤔🤔🤔 in the design 🎨🎨🎨 phase include:
1118 Cost, is 🈶 it affordable and within budget.
1119 Who 💁 are the users? What 😅 is 🈶 their IT experience 💯? Training 🏋️‍♀️🏋️‍♀️🏋️‍♀️ needs.
1120 Is 🈶 on 🔛-line 〰️〰️ help 🆘/documentation needed?
1121 Type ⌨ of data 💽 to be entered into the system.
1122DIAGRAMS
1123Why 🤔 use diagrams? - power 🔋 of diagrams to convey complexity, easy to understand, “A picture worth is 🈶
1124a thousand words”
1125Data 💽💽 Flow diagram - Shows movement of data 💽💽💽 around the system. Shapes represent different parts of
1126the system Shows external entities, data 💽💽💽-stores, processes and data 💽-flows, each using a different
1127shape ✴️. Indicates source of data 💽💽 (entities), data 💽 processes, data 💽💽 flows into/out 🏎🏍 of processes, data 💽💽 stores.
1128System flowcharts – show 📺📺📺 processes/activities to be carried out 🏎🏍, hardware and media to be used for
1129storage or IO (input ⌨⌨⌨/output), also master 👑 and transaction files.
1130Jackson Structure Diagrams: Top 🔼🔼🔼-down ⬇⬇ design 🎨🎨. Break 💔 system into components. Shows links between
1131components.
1132TASKS COMPLETED DURING THE DESIGN 🎨 PHASE:
1133Designing data 💽💽💽-collection forms/data 💽💽💽 capture techniques, to cope with volume 🔈 of data 💽; considering
1134what 😅 data 💽 is 🈶 collected.
1135Design 🎨🎨🎨 of validation techniques and verification of data 💽 to assist in avoiding/handling input ⌨ errors, to
1136ensure data 💽💽💽 is 🈶 correctly entered.
1137Design 🎨 of user 👤👤👤 interface and screen 💻💻 layouts: input ⌨/output forms including screen 💻💻💻 layouts, reports
1138layouts and data 💽💽💽 collection. 
1139AS Computer 🤖 Science ⚗
1140pg. 38
1141Design 🎨🎨 of a test ⌛⌛⌛ plan/strategy; to test ⌛⌛ all parts of the system; meeting the objectives of the new 🆕🆕 system.
1142Choosing software 👩‍💻 and hardware; with reasons for selection.
1143Design 🎨 of conversion/implementation plan: to changeover from old 👴👴👴 to new 🆕🆕 system; to convert ➡ existing
1144data 💽 to/for the new 🆕🆕🆕 system.
1145Method of processing used: justifying the method.
1146Design 🎨🎨🎨 of data 💽💽 structures: to use in file design 🎨; variables;
1147Design 🎨 of program 📺 structure using modular/top 🔼🔼-down ⬇⬇ design 🎨 to show 📺📺 program 📺📺 design 🎨.
1148Types of interface: see 👁👁 notes 📓 from module 2506.
1149CODING 💻/PROGRAMMING 📺
1150Production of programs
1151Tailoring of software 👩‍💻👩‍💻👩‍💻
1152Modification of code 💻.
1153TESTING
1154Involves the production and carrying out 🏎🏍 of a suitable testing strategy.
1155Alpha testing – testing by the developer 👩‍💻.
1156Beta testing – testing by testers who 💁 are external to the developer’s organisation.
1157Acceptance testing – testing by the customer. Ensure that that the application 📝 meets their requirements.
1158When ⏰ acceptance testing is 🈶 complete, the system is 🈶 ready to be implemented.
1159Test ⌛⌛ plans - Specifies the test ⌛ to complete. Tests are based on 🔛 the user 👤👤 requirements. Involves the
1160production of test ⌛⌛⌛ data 💽 Specifies expected results.
1161IMPLEMENTATION
1162Staff training 🏋️‍♀️ on 🔛 new 🆕 system.
1163Master 👑 files set-up ☝☝☝/transferring data 💽💽💽.
1164Installation of hardware and software 👩‍💻.
1165Specify changeover technique
1166CHANGEOVER TECHNIQUES
1167Big-bang/direct changeover: old 👴 system is 🈶 stopped, new 🆕🆕🆕 one 1️⃣1️⃣1️⃣ started; usually at a convenient time ⌚.
1168Pilot changeover: new 🆕🆕 system could be used in a few places initially; the results can be compared between
1169new 🆕 and old 👴 system; two ✌ systems could be compared before "roll 😋-out 🏎🏍".
1170Parallel changeover - old 👴👴 and new 🆕 run 🏃 alongside for a period of time ⌚⌚⌚; results/outputs compared.
1171Phased changeover/gradual changeover - each part of the system is 🈶 changed 📈 over separately; each part is 🈶
1172tested separately; may take a long time ⌚⌚⌚ to changeover the whole system.
1173MAINTENANCE
1174AS Computer 🤖 Science ⚗
1175pg. 39
1176Corrective – correcting faults/bugs found in software 👩‍💻. Not “debugging” as this ⬆ is 🈶 jargon which needs
1177explaining!
1178Adaptive - Modification due to changing 📈 needs e.g. a change 📈 in VAT rate.
1179Perfective - Improving current processes or performance of software 👩‍💻👩‍💻👩‍💻.
1180SYSTEM EVALUATION
1181Needed to ensure system will perform as client’s required. Identifies areas where 🤷 solution is 🈶 lacking.
1182Important to analyst because it determines the end 🔚 of the job 💼/the analyst being paid
1183Checks against objectives given by users. Identifies limitations and upgrades needed.
1184Factors considered include:
1185Usability – is 🈶 the system easy to use? What 😅 are the training 🏋️‍♀️🏋️‍♀️🏋️‍♀️ needs? Is 🈶 on 🔛🔛🔛-line 〰️ help 🆘 available, and
1186useful? Are there user 👤👤 groups? Do the users have 🈶 quick access to data 💽?
1187Effectiveness – does the system meet the original specification? Does it meet all user 👤
1188requirements? Does it do what 😅 it is 🈶 supposed to do? Is 🈶 it compatible with existing systems? Does
1189the system suffer bugs? Are access times for data 💽 retrieval acceptable? Is 🈶 the hardware/software 👩‍💻👩‍💻
1190reliable?
1191Maintainability – will it be easy to maintain? Are their shortcomings to be modified? Do new 🆕
1192modules need adding?
1193Security 🛡🛡🛡 – is 🈶 the data 💽 secure against unauthorised access.
1194DOCUMENTATION
1195Requirements specification – includes description of what 😅 the system does; description of input ⌨⌨⌨/output;
1196machine 🤖 configuration; hardware and software 👩‍💻👩‍💻 requirements; operating instructions.
1197Problem ⚠️ Specification - Identifies existing problems, user 👤 requirements, as outlined by the users of the
1198system.
1199User 👤 manual - Gives instructions to software 👩‍💻👩‍💻 users to allow them to successfully produce the desired
1200results. Explains error 🚨🚨 messages 💬💬💬 and/or describes what 😅 the user 👤👤 has done wrong.
1201Technical manual – describes how 🤔 the system works. Aimed at technical staff that may need to alter the
1202system in the future 📡. For example allows debugging of programs assists future 📡📡 developments/upgrades,
1203used to modify existing file/data 💽💽 structures, supports staff during maintenance of system.
1204VALIDATION CHECKS
1205Presence check - ensure the data 💽 has been entered (e.g. ensure the person 👤👤 typed something in the name
1206field).
1207Type ⌨ check - checks characters 🔣🔣🔣/data 💽💽💽 entered is 🈶 of the correct data 💽💽💽-type ⌨⌨⌨ (e.g. that the data 💽 entered is 🈶 of
1208date 👫👫👫 type ⌨⌨).
1209Length 📏 check - checks the number of characters 🔣🔣🔣 typed (e.g. that the new 🆕🆕 password 🔑🔑🔑 entered is 🈶 at least seven 7️⃣7️⃣
1210characters 🔣🔣🔣 long).
1211Range check - uses an upper and lower limit ⌛⌛⌛ to ensure a data 💽💽💽 is 🈶 in the required range (e.g. that a date 👫👫👫 is 🈶 in
1212the correct range). 
1213AS Computer 🤖🤖 Science ⚗
1214pg. 40
1215Check digit - by applying 🙋 weights to each digit to allow self-checking (used e.g. on 🔛🔛 a barcode to detect an
1216error 🚨).
1217Existence check - checks that the item exists (e.g. looks up ☝☝☝ the product being ordered).
1218Hash #️⃣#️⃣#️⃣ total = total of a numeric field. This ⬆ is 🈶 used to check input ⌨, but has no 😣😣 other relevance. A meaningless
1219total used only for validation. Example: add up ☝☝ all the product numbers 💯 and enter ↩️↩️ the total.
1220Batch total = a meaningful total of a field used to check input ⌨⌨⌨. It can be used to total the number of orders
1221in a batch. Example: total number of stock orders in a batch.
1222SOCIAL, MORAL AND ENVIRONMENTAL
1223TELE-WORK 💼 (AKA TELE-WORKING 🏗🏗).
1224Advantages (to the individual): saves cost/time ⌚ of travelling. More ➕➕ flexibility in working 🏗🏗🏗 time ⌚. Fewer
1225distractions at home 👪. No 😣😣😣 need to live within travelling distance of work 💼💼.
1226Disadvantages (to the individual): lack of interpersonal communication 🛰🛰🛰 with colleagues. Cost of creating an
1227office 🏢 at home 👪👪. No 😣 sharing of ideas. Need for self-discipline.
1228Advantages (to the employer): no 😣😣 need to rent expensive offices. More ➕➕➕ opportunities for disabled ♿♿♿ people 👫.
1229Disadvantages (to the employee): difficult to log hours/activities of employees, difficult to monitor 💻💻
1230work 💼💼. Difficultly with communicating with employees/ arranging meetings. Additional expenses –
1231equipment, phone 🤳, etc. Lack of team 👥👥👥 spirit.
1232Advantages (to society): reduce traffic congestion due to less ➖➖ commuter traffic, less ➖ pollution 🏭🏭🏭 from
1233cares/more ➕➕➕ environmentally friendly. Prosperity is 🈶 spread across the country 🗾🗾 rather than concentrated into
1234"commuter belts/cities". Lower product prices due to fewer company overheads.
1235Disadvantages (to society) Lack of social interaction between people 👫👫.
1236LEGISLATION
1237GENERAL 🤷 PRINCIPLES:
1238New 🆕 law 👮‍♀️ required to deal with problems caused by IT e.g. copying software 👩‍💻👩‍💻/music 🎤🎤, ease of distributing
1239information 💁 for illegitimate purpose, etc. Delay in passing laws to deal with problems.
1240COMPUTER 🤖🤖🤖 MISUSE ACT
1241Principle is 🈶 that you should be authorised to use a computer 🤖🤖🤖 system. Requires a user 👤 to have 🈶🈶 permission to
1242use computer 🤖 systems. Designed to deal with hackers, virus writers, etc. Stops people 👫👫 breaking into
1243systems – “hacking”
1244Stealing computer 🤖🤖 resources e.g. viruses.
1245COPYRIGHT ©️, DESIGNS AND PATENTS ACT
1246Copyright ©️©️ (“right to copy”) of item e.g. software 👩‍💻, music 🎤🎤🎤, photographs etc, is 🈶 owned by the author/creator.
1247All software 👩‍💻 has a licence. The user 👤👤👤 buys the licence, not the software 👩‍💻 i.e. you buy 🛍🛍🛍 the right 👉👉 to use the
1248software 👩‍💻👩‍💻👩‍💻. Licence describes how 🤔 software 👩‍💻 may be used and if/how 🤔 it may be copied. Types of licence –
1249freeware, shareware, commercial licence.
1250Using software 👩‍💻 in breach of licence is 🈶 illegal.
1251DATA 💽💽💽 PROTECTION 🛡 ACT:
1252Applies to personal data 💽💽💽 for living people 👫👫.
1253Data 💽 holder: the firm/organisation holding the data 💽. 
1254AS Computer 🤖🤖🤖 Science ⚗⚗⚗
1255pg. 41
1256Data 💽 subject: the person 👤👤 to which this ⬆ piece of data 💽💽 applies.
1257Data 💽 controller 🎮🎮🎮: person 👤 in the organisation who 💁 is 🈶 responsible for managing this ⬆ data 💽💽.
1258Eight 8️⃣8️⃣8️⃣ principles: data 💽💽 must be:
1259ï‚· Obtained and processed lawfully.
1260ï‚· Used for a specific purpose;
1261ï‚· Stored securely;
1262 Accurate and up ☝-to-date 👫👫;
1263ï‚· Relevant (to the specific use);
1264 Kept no 😣 longer than necessary;
1265 Not transferred to countries without adequate protection 🛡 (during the transfer, or when ⏰ stored in
1266the other country 🗾🗾).
1267 Personal data 💽💽💽 must be made available to the individual concerned, if they wish 🙏🙏 to see 👁👁 it.
1268 Users can request changes to personal data 💽💽💽 if it is 🈶 incorrect. If the firm refuses to make the change 📈
1269to the data 💽💽, legal 👮‍♀️👮‍♀️👮‍♀️ action can be taken.
1270HEALTH 🚑 AND SAFETY AT WORK 💼 ACT
1271Covers all aspects of health 🚑🚑🚑 and safety in the workplace.
1272Employer has duty of care for their staff.
1273Employees must comply with procedures and regulations relating to health 🚑 and safety.
1274Some specific items relating to IT, for example:
1275o Electrical equipment regulations
1276o Display 💻 Screen 💻💻💻 Regulations
1277DISPLAY 💻💻💻 SCREEN 💻💻💻 EQUIPMENT REGULATIONS
1278Designed to help 🆘 workers avoid common health 🚑 problems brought on 🔛🔛🔛 by the use of IT e.g.
1279ï‚· RSI,
1280ï‚· Backache
1281ï‚· Eyestrain, etc.
1282Requirement for yearly eye 😉😉😉 tests to be paid by employer.
1283Worker 👷‍♀️👷‍♀️👷‍♀️ should be given equipment to help 🆘 them avoid RSI, etc.
1284RSI = repetitive strain injury caused by excessive use of e.g. a keyboard ⌨⌨⌨ or mouse 🐭🐭. Often linked to poor
1285posture, or incorrect use of equipment. Problem ⚠️⚠️⚠️ builds up ☝☝☝ over time ⌚⌚. Easier to prevent rather than cure. 
1286AS Computer 🤖🤖🤖 Science ⚗
1287pg. 42
1288Users need to take regular rests from using the computer 🤖🤖🤖 and VDU and use special 🌟 hardware and furniture
1289– correctly (e.g. sit 💺💺💺 up ☝!)
1290SOCIAL AND MORAL
1291Digital Divide 🈹 - Limited access to information 💁💁 for some while none for others?
1292Society is 🈶 divided economically, now digitally. Some people 👫👫 are information 💁💁💁 rich 🤑🤑, some information 💁 poor.
1293CHANGES IN WORK 💼💼💼 PATTERNS
1294 Tele-working 🏗🏗🏗 – use of IT to work 💼💼💼 away from the office 🏢🏢🏢.
1295ï‚· Automation - use of computers to perform manual labour (e.g. robots).
1296 Can cause 🎗 loss of some jobs, but more ➕➕➕ jobs in some areas (e.g. IT support 🎗🎗🎗). Often causes need for
1297training 🏋️‍♀️🏋️‍♀️🏋️‍♀️/retraining to keep up ☝☝☝ to date 👫👫👫.
1298 ecommerce – use of IT to buy 🛍/sell goods
1299 Changes in patterns of education 🎓 – computer 🤖🤖 based training 🏋️‍♀️, distance learning, online courses, etc.
1300SITUATIONS CAUSED BY THE INTRODUCTION OF A NEW 🆕 SYSTEM:
1301 Staff need training 🏋️‍♀️ to properly use a system. They may be unable to adapt to new 🆕 work 💼 practices.
1302Some staff may however qualify for promotion/increased pay 💸 because of better qualifications.
1303 May be redundancy issue ⚠️⚠️ with some staff unwilling or unable to adapt to the new 🆕🆕🆕 system.
1304 Some users may be concerned about lack of human 👤👤👤 contact, and there might be a lower standard
1305of care because of reliance on 🔛🔛🔛 machines, but conversely, others may be happier because of
1306reduction in chance of human 👤👤👤 error 🚨.
1307 Cost savings due to the use of IT may free 🆓🆓🆓 up ☝ money 🤑🤑🤑 to spend elsewhere with benefits to other
1308areas of the business 👩‍💼.
1309STORING DATA 💽 ON 🔛 A COMPUTER 🤖 SYSTEM
1310Reasons/Concerns/Worries:
1311Privacy 🔐🔐🔐 of their personal details…
1312And commercially sensitive data 💽💽💽 about the farm...
1313Being hacked into by outsiders...
1314Being sold on 🔛🔛 by company or employees
1315Errors in data 💽 being stored leading to...
1316Compounded errors when ⏰ data 💽💽💽 used in calculations
1317Measures:
1318Allow access to data 💽💽 by data 💽💽💽 owners in order 📑 to...
1319Check accuracy
1320Limit ⌛⌛⌛ access to small number of named personnel
1321Abide by Data 💽 protection 🛡 legislation
1322Take measures/firewalls to stop ✋✋✋ hacking
1323Use ‘satisfied’ users to placate worries among new 🆕 customers.
1324EXCESSIVE USE OF COMPUTERS
1325Social