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CIE Computer Science Notes, Cheat Sheet of Computer science

Computer science

Chapters from 1-18 from Hodder A level computer science. From an A* student. These comprehensive A-Level Computer Science notes cover the full specification in a clear, structured, and exam-focused way. Designed for quick revision and deep understanding, they include detailed explanations, worked examples, and key definitions presented in concise bullet points. Topics include: ✅ Programming & Algorithms – pseudocode, recursion, Big-O complexity, searching & sorting ✅ Data Structures – arrays, stacks, queues, linked lists, trees, graphs ✅ Computer Systems & Architecture – CPU, registers, fetch-decode-execute cycle, memory, storage ✅ Software Development – compilers, interpreters, OOP, procedural and functional paradigms ✅ Networking & Security – protocols, IP addressing, encryption, firewalls, cyber threats ✅ Databases – relational databases, SQL queries, normalisation (1NF–3NF), DBMS ✅ Logic & Mathematics – Boolean algebra, binary, hexadecimal, floating-point representation

Typology: Cheat Sheet

2023/2024

Available from 08/25/2025

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1: Information Representation

Kibi is binary prefix and kilo is denary prefix

BCD is used to represent values in a clock or calculator

- Straightforward to convert BCD to Denary vice versa

- So less complex to encode and decode for programmers

- Easier for digital equipment use BCD to display output information

- Can represent monetary values exactly

Character set:

- All of the characters that computer can use

- Each character has a unique number

ASCII – 128/ 27

Extended ASCII – 256/ 28

- Each character has its own unique code

- Each character in the word is replaced by its code

- The codes are stored in the order in the word

Unicode:

Has characters from other languages

16 or 32 bits

Pixel:

- Single square of colour

- Smallest addressable element in an image

File Header:

- Colour depth

- Image resolution

- File type – bitmap or vector

- Compression type

- Location/ offset within data

- dimensions

Bitmap:

- Made of pixels

- Large files

- Pixelated when enlarged

- Can be compressed

- Suitable for photos

- Use little processing power

- Individual elements cannot be grouped

Vector Graphic:

- Set of instructions on how to draw shape

- Small files

- Can enlarge without pixelation

- Cannot compress

- More suitable for geometric shapes

- Use more processing power

- Individual elements can be grouped

Partial preview of the text

Download CIE Computer Science Notes and more Cheat Sheet Computer science in PDF only on Docsity!

1: Information Representation

Kibi is binary prefix and kilo is denary prefix BCD is used to represent values in a clock or calculator

Straightforward to convert BCD to Denary vice versa
So less complex to encode and decode for programmers
Easier for digital equipment use BCD to display output information
Can represent monetary values exactly Character set:
All of the characters that computer can use
Each character has a unique number ASCII – 128/ 2^7 Extended ASCII – 256/ 2^8
Each character has its own unique code
Each character in the word is replaced by its code
The codes are stored in the order in the word Unicode: Has characters from other languages 16 or 32 bits Pixel:
Single square of colour
Smallest addressable element in an image File Header :
Colour depth
Image resolution
File type – bitmap or vector
Compression type
Location/ offset within data
dimensions Bitmap :
Made of pixels
Large files
Pixelated when enlarged
Can be compressed
Suitable for photos
Use little processing power
Individual elements cannot be grouped Vector Graphic :
Set of instructions on how to draw shape
Small files
Can enlarge without pixelation
Cannot compress
More suitable for geometric shapes
Use more processing power
Individual elements can be grouped

Need to be rasterised to display or print Property: data about shapes Drawing list: the list of shapes involved in an image Sampling:
Amplitude of wave is determined
At set time intervals
To get approximation of sound wave
And encoded as a sequence of binary number

Increasing sampling rate will improve accuracy of recording
Allow for larger dynamic range
Less sound distortion
Sounds closer to OG o Smaller time gaps between samples o Makes digital sound wave more accurate o Smaller quantisation errors

Produces larger file size
Longer to transmit/download sound files
Greater processing power Important to estimate file size of image so its possible to estimate how many images can be stored and to decide if it can be sent as an email attachment. Image Resolution: the number of pixels in the bitmap file defined as the product of the width and the height values Lossy Compression: Reduce bit depth : reduces number of bits per colour Reduce colour palette: fewer colours mean fewer bits needed to store each colour Reduce image resolution: fewer pixels per unit means less binary to store
human ear will notice decompressed stream will not be identical to original file
Reduces file size more than lossless o smaller files takes less time to transit
Flac (free lossless audio codec) Cannot Lossy compression on text as:
No og data can be lost
Text file would be corrupted Perceptual music shaping: method where sounds outside the normal range of hearing of humans, for example, are eliminated from the music file during compression. Analogue data = data values that are continuously changing Lossless Compression:
File needs to be high precision/accuracy
None of the original data is lost

Users can share files and data
Access to reliable data that comes from a central source – file server
Data and files can be backed up centrally
Users can communicate using email and instant messaging
Network manager can oversee the network and apply access rights

Cabling and servers can be expensive initially
Managing a large network is complex and difficult
Breakdown of servers can affect whole network
Malware and hacking affect whole network Network infrastructure: Hardware:
LAN cards
Hubs o can only broadcast to all connected. o Directionless transmission. o All drop packet except one intended to receive. o Waste of bandwidth
Switches o essentially an intelligent hub. o Sends only to intended recipient.
Repeater o Used to boost signals in the wifi zone. o Sometimes hubs contain repeaters – repeating hubs  One collision domain – ignore this  Referred to as unmanaged since they are unable to manage delivery paths and security
Routers same as hub and switch but also has a modem so can connect to outside of network as well.
In built firewall o receive packets o forward packets to destination o find destination o allocate private IP address o routing table o find most efficient path to destination o maintain table of IP addresses
Bridge o Connects two similar networks o Occurs at link layer in TCP/IP o Main function of bridge is to keep the traffic separated on both sides of the bridge o Format of packet is not changed
Gateway o Connects two dissimilar networks o Packet switches that operate at multiple layers of the OS model o Translate the protocols so that PCs on the two networks can communicate o Format of packet is changed o Do not support dynamic routing
Modem (modulator demodulator)

o Converts digital to analogue and vice versa o Allow several simultaneous wireless communication to take place without interfering with each other. o Router for creating network at home, modem for connecting to external network o Can also have softmodems (software modem) runs on host computer. Computers hardware used instead

Wireless router
NIC – contains MAC address generated at manufacturing stage, usually part of device hardware
WNIC – use antenna to communicate with network via microwaves, usually plug into usb port/integrated circuit plug in. o Can be infrastructure mode – through WAP o Or ad hoc mode – straight to each other o Provides interface to wireless network – as an antenna o Receives analogue radio waves – converts to dig o Checks incoming transmissions for correct MAC/IP address o Ignores unintended o Encrypts and decrypts data o Dig to ana and sends radio via antenna
Repeater
Cabling Software:
Operation of firewalls
Security applications/utilities Services:
Satellite communication channels
Wireless protocols
IP addressing Private networks: owned by single organisation or company often lans or intranets. Company is responsible for purchase of own equip and software, maintenance of network and hiring and training of staff. Public networks: owned by communications carrier company - non passwords, only sub networks may be under security management Client Server Model:
Uses separate dedicated servers; client computers connected to server computer
Users are able to access most of the files which are stored on dedicated servers
Server dictates which users are able to access which files
Client server model allows installation of software onto a client’s computer
Model uses central security databases which control access to the shared resources
Can be as large as wish
Central server looks after storing delivery and sending of emails
Can be bottlenecked (a component that limits the potential of other hardware due to differences in the maximum capabilities of the two components) if several client requests at the same time
E.g. amazon Choose because:
Company has large user base

Each node looks at each packet and determines whether or not the address of the recipient in the package matches the node address. If so the node accepts the packet, if not, packet ignored. Suitable for situations w small no of devices with light traffic e.g. small company or office

Uses single central cable to which all computers and devices are connected.
Typically peer to peer
Data only travels in one direction
If data is being sent other devices cannot transmit
Terminators are needed at each end to prevent signal reflection (bounce)
If main cable fails, whole network goes down
Performance of network deteriorates under heavy loading
Every packet passes through every node so not very secure

Even if one node fails, remainder of network continues to function (bc p2p)
Its easy to increase size of network by adding additional nodes Star Network Used for evolving networks where devices frequently added or removed. Well suited to heavy traffic

Uses central hub/switch which each computer is connected to
Data going from host to host is directed through central switch/hub
Each computer/device has its own dedicated connection to central node
Usually client server
Hub: o Packets sent to every node o If address matches node, its accepted otherwise not
Switch: o Packets only sent to node with address o This is more secure
High initial installation costs
If central hub/switch fails, whole network goes down
Data collisions reduced

Secure bc: o Security on central Hub/switch o Packets only sent to receiving node
Easy to upgrade by j changing hub/switch
If one connection breaks, only that node is affected Mesh Network

Routing o Giving nodes routing logic so data is directed by shortest route and can be re- routed if one of the nodes in the routes have failed
Flooding o Simply sends the data via all the nodes and uses no routing logic. Can lead to unnecessary loading on the network
Peer to peer
Used in interent, WANs, MANs
Industrial monitoring and control systems
Large amount of cabling – expensive and time consuming
Set up and maintenance is difficult and complex

Easy to identify where faults on network in network have occurred
Any broken links in network do not affect other nodes

Good privacy and security since packets travel along dedicated routes
No collisions
Network is relatively easy to expand Hybrid Network Mixtures of two or more different topologies
Can handle large volumes of traffic
Easy to identify where a network fault has occurred
Very well suited to the creation of larger networks Cloud:

Cloud computing: accessing a service, files, software on a remote server
Public cloud: where client and cloud provider are diff companies
Private cloud: provided by dedicated environment behind company firewall. Client and cloud provider operate as single entity
Hybrid cloud: combination. Some data in private and less sensitive data in public

don’t need separate storage devices
can access from any computer w internet connection
cloud services often have backups
data is easily shared
can easily increase capacity

need internet to access
time needed to upload/download data
expensive in long term
limit to amount of storage paid for Wifi and Bluetooth When a device wants to communicate it picks one of the 79 channels at random, if this is being used, it randomly picks another – spread spectrum freq. hopping. To minimise interference, constantly switch frequencies. Bluetooth create secure WPAN (wireless personal area network). Useful when:
transferring data between 2 or more devices which are less than 30 metres apart
speed of data transmission is not critical
low bandwidth applications Bandwidth: radio  micro  infrared Penetration: infrared  micro  infrared Attenuation: infrared  micro  radio

easier to expand networks not necessary
devices have increased mobility
less cabling/expertise needed

increased chance of interference
data is less secure than with wired systems
signals can be stopped by thick walls Satellite

On demand:

Digital files stored on server converted to bit streaming format
Link to encoded file is put on web server
File is downloaded in contiguous bit stream, can rewind and fast forward Real time:
Event captured by camera and microphone
Video signal encoded to streaming media file
Encoded file is uploaded to computer from dedicated video streaming server
Server sends encoded live video to user’s device
Video footage is live so cant rewind etc Internet Network of networks Uses TCP/IP Need ISP (internet service eprovider) to access it WWW Collection of multimedia webpages Uses https for HTML pages Need web browsers PSTN Alternative to internet (VoIP – Voice over Internet Protocol) to make a phone call Always open until line is terminated by both ends They have their own power source so unaffected by powercut Use circuit switching VoIP Converts sound to digital packages Uses packet switching Carries out file compression More efficient than PSTN – inly necessary data is transmit Can also use satellites – don’t suffer from attenuation IP address Ipv4:
Set of 4 numbers
Each number is 8 bits
Separated by dots Ipv6:
Set of 8 numbers
Each number is 4 hex digits – 16 bits
Separated by colons Public IP: visible to any network on device Private IP: visible to only networks on LAN Static IP:
When a computer disconnects and rejoins a network, address doesn’t change
Address assigned by Dynamic IP:
Each time computer rejoins, IP changes
Assigned by network OS

Subnetting: Network ID is first part, then host ID

Reduce amount of traffic in network
Sata stays in subnet – does not travel far
Improves network security- not all devices can access all areas of network
Allows for easier maintenance
Only one subnetwork breaks, rest can continue MAC address:
Hex
Doesn’t change
Identify on LAN DNS – domain name service User opens web browser and types in URL, web browser askes DNS server for IP address of website DNS server can’t find URL in its database and sends req. to diff DNS server. This server finds URL and maps it to IP address, this is sent back to OG server (stores this info) IP address is sent back to user’s computer Computer sets up communication with website server and req. pages are downloaded. Browser interprets HTML and displays

3: Hardware

Cache Memory

high speed memory external to processor which stores data which the processor will need again. Closer to CPU than primary memory

Primary Memory

RAM:

Random access memory write/read by user and computer stores: data, files, part of an app, part of OS thats currently in use volatile

faster than ROM DRAM : (Dynamic RAM) type of RAM that needs to be constantly refreshed as capacitors leak electricity
less expensive than SRAM
consume less power
higher memory capacity SRAM : (Static RAM) uses flip-flops does not need refreshing used in cache
faster data access time than DRAM Flipflops:

can either store either 0 or 1
computers use bits to store data
can be used to store bits of data

Magnetic Storage
Central spindle
Platter made of aluminium
Spins fast at high speed
Head
Moves with electric current
Has concentric tracks
one track in one sector is called one block
data is encoded as a magnetic pattern for each block

cheap

slow data access time. lots of latency
can be damaged if dropped Solid State:
Non volatile
Secondary storage
Stores data by flashing it onto chips
Stored by controlling flow of electrons using transistors
Current reaches control gate and flows through the floating gate to be stored
When data is stored the transistor is converted from 1 to 0
if flash memory, NAND chips
if EEPROM, NOR chips (faster. expensive)

robust and more physically durable
No moving parts
No lag time (don’t have to get up to speed)
Cooler
thinner
faster read/write

unknown longevity
expensive Optical :
Drive motor spins disc
Lens focus laser onto disc
Laser is shone to read/ write
Disc has reflective metal layer
Track has sequence of pits n lands
Reflected light is encoded as a bit pattern [CDs + DVDs can be R (write once) or RW (read/write multiple times) DVDs are dual layered so higher storage Blu-ray uses blue laser (smaller wavelength) so smaller pits therefore more storage] Dual Layering: Two layers of a standard DVD are joined together with a transparent (polycarbonate) spacer, and a very thin reflector is sandwiched between the two layers. Reading and writing of the second layer is done by a red laser focusing at a fraction of a millimetre difference compared to the first layer. however can cause birefringence (reading problem with DVDs caused by refraction of laser light)

Hardware:

Binder 3D Printing: 3D printing method that uses a two-stage pass; first stage uses dry powder and second stage uses binding agent Direct 3D Printing: 3D printing technique where print head moves in xyz directions. layers of melted material are built up using nozzles like an inkjet printer Laser Printer:

The drum is given an electric charge.
The drum starts to revolve step by step.
At each step a laser beam is directed by the mirror and lens assembly to a sequence of positions across the width of the drum.
At each position the laser is either switched off to leave the charge on the drum or switched on to discharge the position.
This process repeats until a full-page electrostatic image has been created.
The drum is coated with a charged toner that only sticks to positions where the drum has been discharged.
The drum rolls over a sheet of paper which is initially given an electric charge.
The sheet of paper is discharged and then is passed through heated rollers to fuse the toner particles and seal the image on the paper surface. - The drum is discharged before the process starts again for the next page Inkjet Printer: non-impact printer line printer
print head contains large number of very small nozzles
ink is fed to each nozzle from a reservoir
print head fires droplets of ink onto paper
it moves horizontally across paper thermal bubble:
tiny resistors create heat inside each nozzle
heat vaporises ink to create a bubble
when the bubble pops ink is deposited on page
collapsing bubble creates partial vacuum in nozzle
ink is drawn from reservoir for next page piezoelectric crystal:
piezo crystal at back of ink reservoir of each nozzle
crystal vibrates when it receives electric charge
ink is forced out of nozzle by inward vibration
outward vibration creates partial vacuum in nozzle
replacement ink is pulled into reservoir
stepper motor connected to print head by a belt
moves print head across paper
parks print head when not in use
stepper motor connected to paper feed turns rollers that provide paper Buffer:
temp storage
before used by receiving device
to allow processes to operate a different speeds
independently of each other a temporary storage created for data transmitted from one part of the system to another which functions as a queue

as mouse moves, sensor detects change in surface detail
translated into movement
computer updates position of cursor on screen Keyboard:
keys are positioned above a key matrix which consists set of rows and wires and another set of columns of wires
pressing a key causes contact at one of the points where wires cross
microprocessor continuously tests to see if any electrical circuit involving a row wire and a column wire has been closed
when microprocessor recognises that a circuit has become closed, it can identify the particular intersection that is causing this
processor uses data stored in the ROM to identify the character code relating to the associated key and sends the character to screen Scanner: sheet of paper containing image held in fixed position and light source moves across it. covers width of paper reflected light directed by mirrors and lenses onto CCD (charged couple device)
CCD contains array of photosensitive cells
produces electrical response proportional to light intensity for each cell
needs ADC to transmit values to computer VR headset:
two eye pieces
fed paired images from the controlling system so that it gives the eyes the sensation of being in a 3D environment.
get the images by using specialised photographic techniques or using a 3D graphics package.
the wearer of the headset controls which part of the 3D env they see by moving their head.

Systems

Control:

sensors send signals to computer/microprocessor
signals converted to digital using ADC
microprocessor analyses data received by checking against stored values
if new data outside range, microprocessor sends signals to control valves, motors etc
output from system affects next set of input from sensors. Gives feedback bc:
to ensure the system operates within the given criteria
by enabling system outputs to affect subsequent system inputs
the system automatically adjust conditions Monitoring:
sensors send signals to computer/microprocessor
signals converted to digital using ADC
microprocessor analyses data received by checking against stored values
if new data outside range, warning message is sent ot screen/alarm activated
microprocessor has no effect on what is being monitored, simply watching Control vs monitoring: Control uses feedback

Control produces an action Sensors:

temperature
pH
motion
pressure
humidity
sound

4: Processor Fundamentals

Stored program concept: Instructions and data are stored in the same memory space / in main memory Von Neumann Model:

CPU(Central Processing Unit)
CPU has direct access to memory
memory contains 'stored program' and data required by program
stored program consists of individual instructions
processor executes instructions sequentially Internal Clock: controls cycles of activity within processor System clock:
synchronise operations
by creating timing signals
to keep track of date and time
to process operations in correct order/ sequence controls cycles of activity outside the processor. By increasing clock speed, processing speed of computer is also increased.
One instruction per cycle, hence faster clock speed = more instr/ sec This doesn’t necessarily mean increase in performance need to also consider:
width of address bus and data bus can affect computer performance
overclocking: when speed is changed by accessing BIOS (basic input output system) o execution of instructions outside design limits – leads to unsynchronised operations o overheating of CPU
use of cache memory can improve processor performance. Cache is volatile and uses SRAM (unlike main memory) hence faster access time
use of a different number of cores ALU: (Arithmetic logic unit) responsible for arithmetic or logic processing requirements of the instruction in a running program Control unit:
to coordinate / synchronise the actions of other components in the CPU
to send / receive control signals along the control bus
to manage the execution of instructions (in sequence)
to control the communication between the components of the CPU
has internal and system clock
CPU has clock speed - defined frequency for clock cycle:
the minimum period of time that separates successive activities within the system.

Simpler tech
Only 1 standard available
Easy to split signal and connect a number of devices from one source

Old analogue tech
Easy to bend pins when connecting
Cable must be very high grade to ensure good signal HDMI: (High Definiton Multimedia Interface) provides high-quality video and audio (newer VGA)

Current standard for modern TVs and monitors
Allows for a very fast transfer rate
Improved security

Not very robust connection
Limited cable length
Currently 5 cable standards FDE cycle: PC contains address of memory location of next instruction to be fetched Address then copied from PC to MAR using address bus Instruction at address contained in MAR are copied temporarily into MDR Instruction of MDR placed in CIR PC incremented Instruction is decoded then executed by sending out signals via control bus to various components of system Check for interrupts then repeat. Interrupts:
Check for interrupt at end of cycle
Priority is checked
If lower, leave; if higher, store current process on stack
Location of interrupt identified
ISR called
Check again for more interrupts
If higher, repeat; if lower, load data from stack and start FE cycle Software:
Division by zero
Attempts to access invalid memory location
Array index out of bounds
Stack overflow Two Pass assembler: There are 2 types , single pass and 2 pass. Single pass puts machine code straight into computer memory to be executed Pass 1: to create a symbol table
Read assembly language program line by line
Ignore comments

Allocate memory address for line of code
Check opcode is instruction set
Add new labels to symbol table with address if known
Place address of labelled instruction in symbol table Pass 2:
Read assembly language program line by line
Generate object code including opcode and operable from symbol table in pass 1
Save /execute Adressing Immediate then direct/absolute then indirect. Indexed is indirect address+ contents of IR. Eg. Current instruction contains 4 and IR contains 6, address is 10. Relative is current memory address plus #n spaces.
To allow for re-locatable code
Because all target addresses can be specified by the base address + offset Symbolic (only exists in assembly) is when theres a label Instruction groups Data movement Arithmetic operations: perform addition and subtraction Input and output of data: takes input from user// outputs char of binary no. (un)conditional: move to another instruction Compare instructions: compare result to another value Binary Shifts Logical shift: bits shifted out are replaced w 0s Arithmetic shift: sign is preserved. Can be used for multiplication and division by powers of 2.

5: System Software

User Interface:

CLI – hardware: keyboard
GUI – Hardware: mouse Why does computer need OS? Hardware is unusable without an OS acts as interface between user and hardware Provides software where other programs can be run OS:
Memory management o Memory optimisation - Determines where in memory its stored o Memory organisation – determines how much of memory it uses o Memory protection – ensures two apps don’t use the same locations RAM allocation: o RAM is assigned into blocks o dynamic allocation of RAM to programs / processes o reclaims unused blocks of RAM

CIE Computer Science Notes, Cheat Sheet of Computer science

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Partial preview of the text

Download CIE Computer Science Notes and more Cheat Sheet Computer science in PDF only on Docsity!

1: Information Representation

3: Hardware

Cache Memory

Primary Memory

RAM:

Hardware:

Systems

4: Processor Fundamentals

5: System Software