Concise Notes
Information Representation
Data Representation
BCD Benefits: Straightforward conversion to denary, less complex encoding/decoding, exact monetary representation.
BCD Applications: Electronic displays (calculators, clocks), BIOS date/time storage.
Hexadecimal Applications: MAC addresses, HTML color codes, memory addresses (assembly/machine code).
ASCII Representation: Unique code per character, codes stored in word order.
Character Set: All representable characters with corresponding binary numbers.
Similarities: Can use 8 bits, ASCII is a subset of Unicode/EA, unique code usage.
Differences: Unicode supports more languages/characters, varying bit sizes (ASCII - 7bit, Extended ASCII - 8bit, UNICODE - 16bit).
Multimedia
Graphics
Bitmap Graphic
Pixels of single color, stored as binary.
Prone to pixelation, larger file size, difficult to edit.
Can be significantly compressed.
Pixel: Smallest addressable element.
File header: Metadata (color depth, resolution). Stores file type, compression, dimensions, file size.
Image Resolution: Total pixels (width * height). Higher resolution = sharper image.
Bit/Color Depth: Bits per color, determining representable colors. Higher bit depth = more colors, larger file size.
Vector Graphic
Instructions to draw shapes.
No pixelation upon scaling, individual component editing.
Smaller file size, poor compression due to minimal redundancy.
Drawing Object: Component created via formula/command.
Drawing Property: Shape appearance data.
Drawing List: Image shapes/drawing objects.
Vector Graphic Representation: Geometric shapes, drawing object coordinates, drawing list (commands & attributes).
Sound
Sound Representation
Amplitude recorded at intervals, each with binary value.
Binary numbers are stored in sequence.
Sampling: Measurements at regular intervals.
Sampling Rate: Samples per unit time (second).
Effect of increasing sampling rate: Recording more often, reduces quantisation errors, improves accuracy, increases file size.
Sampling Resolution: Bits to store each sample.
Effect of increasing sampling resolution: Increases bits per sample, wider amplitude range, increases file size, improves accuracy, smaller quantisation errors.
Analogue data: Constantly changing variable/data value.
Compression
Compression Reasons
Smaller file size, faster transfer, less bandwidth.
Original file too large for email.
Lossy Compression
Data loss, non-reconstructible files.
Text file corruption.
Lower video resolution, less buffering, reduced bandwidth.
Acceptable when full data isn't critical or significant size reduction is necessary.
Lossless Compression
Original data preserved.
Essential for full restoration, high quality, or small files.
Compressing Files
Sound
Reduce amplitude range, run-length encoding (RLE), record changes only.
Images
(Lossy) Reduce bit depth/colors, reduce resolution.
(Lossless) RLE.
Run-Length Encoding (RLE)
Replaces repeated character sequences with character and repetition count.
RLE Limitations: Inefficient if few repeating sequences; can increase file size.
Communication
Networks Including the Internet
LAN
Enables communication/data and resource sharing, central management.
Small area, physical connections, private ownership.
High data transfer rate, easier security.
WAN
Large area, virtual connections, public or private ownership.
Low data transfer rate
Client-Server Model
Web pages/data on servers, client requests processed and returned.
Users' computers are clients.
Users can request files from any client computer.
Files can be accessed simultaneously by several users.
Peer-to-Peer Network Features
Computers are of equal status
Each computer provides access to data an resources
Computers can communicate and share resources
Computers are responsible for their own security
Drawbacks of a Peer-to-Peer Network
Reduced security (no central management of security)
No central management of back-up
No central management of files
Computers have slower response time (due to being accessed by other computers)
Files may not always be available
Thick-Client
Server performs minimal processing for client
Most resources are installed locally
Clients do most of the processing independently
Thin-Client
Server performs all processes required by task/data storage
Clients only send requests to server and displays returned results
Star Topology
Devices only connected to central router/device (switch/hub etc.)
Each computer only connected server
Fewer collisions, easily scalable, more resilient
How Data is Transmitted
Data from sending device is transmitted to the router
Data has address of recipient
Router determines recipient's destination address - using routing table
Router transmits data directly/only to recipient
Mesh Topology
All computers connected to at least one other device
Multiple routes between devices
Computers can act as relays - forward packets to final destination
Advantages of Mesh Topology
If one line goes down, alternate routes are available
Improved security (not using one main line)
Fewer collisions (more routes available)
New nodes can be added without interfering with others
Cloud Computing
Accessing a file/service on a remote server
Public Cloud:
Services offered by a third party over public internet, available to anyone with appropriate software/equipment
(resources available on Internet, available to anyone)
Private Cloud:
Services offered by a private internal network, only available to select users (not general public), dedicated system only accessible from the organisation
Advantages
Can be free
Saves storage on existing devices
Data can be accessed from any device (with internet access)
Data will likely be backed up/ higher chance of recovery
Better security
Scalable & easily shared
Disadvantages
Only accessible with internet access
Can take a long time to upload/download the data
Can be expensive (long term)
May have limited storage space for free
May not have backup/recovery or security options
You are reliant on someone else/dependant on third party (for security or backup)
Can't access files if server goes down
Disadvantages of Public Cloud
Loss of control (data is stored on remote infrastructure, relies on external provider)
Requires reliable internet connection to access data
Increased recurring costs (provides charger must be paid, LAN is one-time only)
Advantages of a Wired Network (better performance, faster access)
Higher bandwidth (less latency - good for streaming larger files)
More reliable/stable connection (less vulnerable to interference (distance/walls))
More secure (confidential data can be transferred securely)
Advantages of a Wireless Network
Freedom of movement (not fixed to a single location) - can move between rooms, no need for physical connection (devices can be portable)
Easily expandable/scalable if more devices want to join (ppl can join on multiple devices)
Less cabling needed (cheaper setup)
Allows access in remote locations (e.g. rural areas)
Disadvantages of a Wireless Network
Higher latency
Affected by weather
Slower transmission speed
Direct line of sight needed
Copper Cables
Data is transmitted through electrical signals
Lower transmission rate
Chance of interference and interception
Require repeaters over long distances
More sturdy/reliable/flexible
Fibre-optic Cables
Data is transmitted using light
Has a greater bandwidth and faster transmission speed
Smaller risk of interference
Can be used over long distances (needs less signal boosting)
More difficult to hack into
More prone to damage, less flexible/can break when bent, more expensive to install, difficult to terminate
Radio Waves
Carries data wirelessly as electromagnetic waves.
Satellite
Communication device in Earth's orbit.
Receives and transmits data.
Switch
Allows communication between devices
Connects individual devices to each other
Server
Receives transmissions and forwards them to their destination
Manages access to a centralised resource (usually between devices on LAN)
Functions of WNIC
Provides interface/allows connection to wireless network as an antenna
Receives analogue waves and converts them to digital
Takes digital input and converts it into analogue waves (sends radio waves through antenna)
Encrypts and decrypts data
Provides MAC address to identify device on the network
WAP
Hardware providing radio communication between a central device and nodes in a network
Allows connection of devices using radio waves/signals/Wi-Fi
Allows wireless enabled devices to connect to wired network
Bridge
Connects two LANS with the same protocol
Allows communication/data transmission between two networks with same protocol
Repeater
Restores a digital signal so it can be transmitted over greater distances
Role of Router
Receives packets from devices // external network/internet
Stores IP and MAC addresses of all devices attached to it
Maintains routing table
Routes forwards/packets to destination
Finds destination of a packet (using IP addresses)
Assigns private IP addresses to devices on a LAN
Finds most efficient path to destination
Can act as a firewall, gateway ( + perform protocol conversion/ changes packet format)
Ethernet
A protocol, uses CSMA/CD, transmits data in frames (source, destination, error checking).
CSMA/CD (protocol)
Used to detect and prevent collisions
Device/node that listens to a communication channel (scans voltage)
Data is only sent when channel is free/idle (line is empty)
As there are multiple nodes on network/topology…
Data from two nodes can start to transmit simultaneously, causing collision
If collision occurs, nodes send signal to stop transmitting
Waits a random time before attempting to send data again
Bit Streaming
Data is compressed before transmitting
Video is transmitted continuously as a series of bits
On download, the server sends data to a buffer on the client computers
Recipient receives bit stream from the buffer
Real-time
Used when watching a live stream of events that are currently taking place
Event is captured live with a video camera connected to a computer
Media is sent to user's device/buffer via bit stream directly as it is being recorded
Cannot be paused or rewound
On-demand
Video is already recorded/event has taken place
Existing media is encoded to bit streaming format and uploaded to a server
Can be watched at user's convenience (can be paused/forwarded or rewound)
Difference Between the WWW and the Internet
WWW
Uses http/https protocol to transmit data
Collection of web pages
Internet
Uses TCP or IP protocols
Interconnected network of networks
Hardware Supporting the Internet
PSTN
Consists of many different types of communication lines
Allows for full duplex data transmission
Communication passes through different switching centres
Line remains active even during power outage
Dedicated channel used between two points for duration of phone call
Networks Including the Internet - Continued
IPv4
4 groups each represented by 8 bits (32bit)
Either denary or hexadecimal with numbers between 0-255 (in each group)
Separated by full stops
IPv6
8 groups each represented by 16 bits (128bit)
Hexadecimal numbers between 0 and FFFF
Groups only contains 0 can be replaced with ::
Separated using colons
Used when the number or IP addresses needed exceeds number available using IPv4
Subnetting Benefits
Improves security (data stays in its subnet, not all devices can access all areas of network, devices do not receive unintended data)
Allows extension of network/easier to expand (allows greater range of IP addresses)
Reduces amount of traffic in a network (improves network speed, data stays within subnet and devices are not flooded with data)
Easier maintenance/management (only one subnetwork may need taking down, rest can continue/faults can also be isolated more efficiently)
IP Address in Subnetwork
Made up of network ID and host ID
Each device on subnetwork has same network ID (each subnetwork has different network ID)
Every device in each subnetwork has different host ID but the same network ID
Host ID uniquely identifies device within the same subnetwork
Public IP Address
Is visible to any device on the internet
Assigned to allow direct access to the internet
Allocated by ISP
Unique throughout internet
Private IP Address
Only visible to devices within the LAN
Used for internal LAN communication only
Allocated by router
Only unique within LAN
Dynamic IP Address
New one is reallocated each time a device rejoins a network
Static IP Address
Does not change each time a device connects to the internet (is fixed)
URL, WWW and DNS Use
A URL is entered into web browser and parsed to obtain the domain name
The Domain name is sent to DNS
DNS has database of domain names and their corresponding IP Addresses
DNS searches its database for given domain name
If found, the IP addresses is returned to web browser, which displays the resource
If not found, the request is forwarded to a higher level DNS and the IP addresses returned is added to the database of the lower level DNS
Hardware
Computers and Their Components
Need for Secondary Storage
To store files/data/ software long-term
Need for Primary Storage
To store files needed to boot system
To store OS or any system software
To store intermediate data/ current data
Embedded System
Microprocessor within a larger system that performs a specific task
Has memory, input/output abilities, and a processor
integrated into machine, not easily changed (by user/owner)
E.g., a system in a washing machine that only controls cycle programs
Combination of hardware and software designed for a specific function
Does not have its own operating system
Does not require much processing power
Disadvantages
Difficult to change/update firmware by user (difficult to upgrade to take advantage of new technology)
Cannot be easily adapted for another task
Difficult to update/repair (usually thrown away instead)
Operation of Laser Printer
Revolving drum gets electrical charge.
Laser draws page content electrostatically.
Toner sticks to charged areas.
Drum rolls toner onto charged paper.
Fuser heats paper to seal image.
Drum charge removed, toner collected.
Operation of 3D Printer
Additive manufacturing.
Uses digital 3D model or CAD file
builds up model one layer at a time - starting from bottom, using xyz coordinates
Material is fused together layer by layer
Fused Deposition Modelling (material is heated and pushed through nozzle)
Use of Temperature Sensor
Prevents overheating/ensures the material is hot enough
Identifies material of object/material being used
Microphone Operation
Diaphragm vibrates from sound waves
Coil moves past magnet
Electrical signal produced
Speaker
Electric current passes through a coil.
Electromagnetic fields cause diaphragm vibration.
Vibrations create sound waves
Magnetic Hard Disk
Platters divided into sectors and concentric tracks, surface can be magnetised
Read/write head on arm, data encoded as magnetic pattern
Writing (current variation causes magnetic field variation), reading (magnetic field variation causes current variation)
Advantages
Costs less per unit storage(used when large storage capacity is required)
Has more longevity (used with devices that work all the time and have a large number of read-write operations
Solid State Memory
Grid of columns and rows (arrays/blocks, two transistors at each intersection)
Not possible to overwrite existing data (need to erase first then write data into location)
Floating gate (stores voltage, represents a 1 or 0)
Control gate (controls movement of charge/electrons during read/write operations)
Advantages
No moving parts - more reliable
Faster data access times
Optical Disk Reader/Writer
Rotating disk with tracks of reflective metal.
Laser reads/writes using light.
Data stored in pits and lands (amorphous/crystalline states)
Reading (reflected light encoded as bit pattern), writing (laser changes surface state based on bit pattern)
Read and write operation can occur simultaneously
Features/Uses
Used for transferring data between devices or as back-up systems
Can be read-only (used to distribute software, movies or games
Generally have lower storage capacity
Resistive Touch Screen
Two layers touch to complete a circuit.
Processor determines touch point.
Works with any object.
Capacitive Touch Screen
Change in electric current when the top layer is touched.
Microprocessor IDs touch coordinates
Virtual Reality Headset
Video/data sent from computer.
LCD/OLED display.
Lenses create 3D effect.
Sensors track movement.
Binaural sound.
Infrared sensors monitor eye movement.
Purpose of a Buffer
Temporarily stores data until it is ready to be transmitted to the device
Stores data before it is used by receiving device
Allows processes to operate independently of each other
E.g., video buffer when streaming videos, printer buffer when data is transferred from computer to printer and allows user to continue using computer.
When buffer is empty, an interrupt is sent to computer, requesting more data
RAM
Primary memory, volatile
Stores running software/data/OS/processes
Static or dynamic, stores I/O data, buffer contents, process information
SRAM (flip-flops, complex), DRAM (transistors/capacitors, charge)
SRAM Advantages/Disadvantages
Faster access time - because it does not need to be refreshed
Used on CPU for performance (used in cache memory)
Has lower data density
Does not need to be refreshed (consumes less power)
DRAM Advantages/Disadvantages
Costs less per unit
Higher storage/data/bit density – more data stored per chip
Simpler design (fewer transistors)
Needs to be refreshed (higher power consumption)
Slower access speed (used in main memory)
ROM
Primary memory, non-volatile
stores startup instructions/BIOS, firmware, permanently required data
Stores the kernel of the operating system
PROM (set once), EPROM (UV erase, rewrite), EEPROM (voltage erase, rewrite)
Use in Embedded Systems
To store data that does not change e.g. boot up instructions
Data must be stored when device is powered off
Control Systems
Use feedback & produce an action.
Role of Actuator
generates signal converts electrical energy into mechanical energy
to produce an action (be specific to situation)
Importance of Feedback
Ensures system operates within given criteria
Allows system output to affect system input
Allows conditions to be automatically adjusted
Logic Gates and Logic Circuits
No details provided in transcript
Processor Fundamentals
CPU Architecture
Stored Program Concept
Instructions and data stored in same memory.
Components in Von Neumann Architecture
Buses, Registers, CPU, CU, ALU, IAS, System clock.
General Purpose Registers
Hold temporary data during operations
Used for any purpose
Can be used by most instructions
Special Purpose Registers
Hold status of a program
Specialised for specific use
Can only be used by certain instructions
*
Program counter, Memory Address Register, Memory Data Register, Current Instruction Register, Index Register, Status Register
Control Unit (CU)
Synchronizes CPU components, sends/receives control signals, manages instruction execution, controls communication between components.
Types of signals it transfers: interrupt, timing, read & write.
System Clock
Synchronises computer operations by creating time signals
Allows operations to be processed in the correct order / sequence
Keeps track of date and time
Immediate Access Store (IAS)
Holds all the data/programs currently in use
Volatile memory, fast access times
How Data is Transferred Between Components
System clock provides timing signals - sent on the control bus, this synchronizes the other system components
CU initializes data transfer - generates signals that are sent on control bus to other components
Role of Buses in Storing Data
Address bus (carries address to/from memory)
Data bus (carries data between devices and buffer)
Control bus (carries control signals from CU
Performance
Number of Cores
Process one instruction per clock pulse, more sequences simultaneously.
why this may not increase performance
Software may not be designed for multiple cores
Limited by memory access speed
Limited by other aspects - e.g amount of RAM
Bus Width
Allows transfer of more data each time/each transfer
Clock Speed
Instructions carried out on clock pulse
Clock speed dictates instruction rate
Faster clock speed = more instructions can be run per second/time period
Cache
Fast access memory (close to CPU)
Stores frequently used instructions/data
More cache means more instructions can be transferred faster - less swapping between RAM and cache
Prevents CPU idling while waiting for data
Quantity of RAM
More applications can reside in main memory simultaneously
Saves/decreases disk access times
Ports
Purposeto provide connection to peripherals and interface between computer and other devices
*
USB // COM port (fast data transfer, universal).
HDMI (video & audio on one cable).
VGA
Display Port
Fetch-Execute Cycle
PC stores the address of the next instruction to be fetched contents incremented each cycle
MAR holds address where data is fetched from (from which data will be read from/written into)
MDR holds data at/from address in MAR (or data to be entered into it)
Instruction (from MDR) is copied to CIR for decoding and execution
Register Transfer Notation
Stages of the FE Cycle
Purpose of an Interrupt
Causes of Software Interrupt
Causes of a Hardware Interrupt
Interrupts
Two-Pass Assembler
First Pass (create symbol table): Reads assembly, removes comments, adds labels.
Second Pass: Generates object/machine code.
Instruction Groups
Data movement, Input/Output, Arithmetic, Unconditional/Conditional, Compare
All types of addressing load contents of given/calculated address into accumulator
Immediate Addressing
Operand is the data
Direct Addressing
Operand holds memory address of data
Addresses address given by operand
Indirect Addressing
The address used is at the address the user gives
Operand holds memory address that stores the memory address of the data
Indexed Addressing
Forms address from given address/address in operand plus the contents of the index register
Relative Addressing
the address to be used is an offset number of locations away, relative to the address of the current instruction, relocatable code supported
Bit Manipulation
Binary shifts, Logical shift, Arithmetic shift, Cyclic shift, left shift, Right shift, bit masking (AND, OR, XOR)
System Software
Operating Systems
To provide a user interface
To provide a platform for software to run
To hide complexities of hardware from user
Operating System - Management tasks (memory, file, security, hardware, process, input/output, error checking, recovering)
Memory Management
Controls movement of data between RAM/processor
Allocates memory to processes
Dynamically allocates memory to processes/programs
How MM Allocates RAM
RAM is assigned into blocks.
Dynamic allocation of RAM to programs
Reclaims unused block of RAM
Prevents two programs occupying same area of RAM simultaneously
Moves data from secondary storage when needed (manages paging virtual memory)
File Management Tasks
Space allocated to particular files
Maintains a directory structure
Provides file naming abilities
Implements access rights
Allows file sharing
Specifies tasks that can be performed on a file (copy, paste, delete, close…)
Security Management
Creates accounts/passwords
Provides firewall or anti-malware
Validates user and process authenticity
Hardware Management
Receives data from input devices/ sends data to output devices
operates/installs device drivers install programs for devices connected to external ports
Allows communication between peripheral devices and computer
Handles buffers for transfer of data (ensures smooth transfer between devices transmitting and receiving at different
Manages interrupts from devices
Process Management
Manages scheduling of processes (decides which process to run next/order of processes)
Manages resources the processes require (e.g allocating memory)
Enables processes to share/transfer data
Prevents interference between processes
Handles process queue
Supports multitasking (ensures fair access, handling priorities, interrupts)
Utility Software
help set-up/optimise/ maintain the computer
makes memory allocation more efficient
checks the system for faults
Disk formatter (prepares disk for use)
Defragmentation (rearranges files sequentially, improves speed)
Disk repair is needed to optimize performance
Back-up (Software) (allows retrieval of data, provides security against loss)
Disk/System clean-up
Compression software (reduces file size)
Virus Checker
Program Library
Provides pre-written functions and subroutines, which can be called in own program
Dynamic Link Library Benefits (requires less main memory, executable file is smaller, no maintenance for programmer, no need to recompile program if changes are made)
Language Translators
Convert high-level/assembly to machine code.
Assembler
Translates assembly code into machine code
Compiler
Translates entire high-level language code at once, produces executable, errors reported after translation, used after program is complete
Drawbacks (cannot be changed without recompilation)
Advantages (develop can test program without recompiling)
Interpreter
translate high-level language line by line is translated then run, used while writing a program for testing and debugging, errors corrected in real-time during testing. Small part tested individually, can avoid dependant errors
IDE Features/Tools (coding, error detection, presentation, debugging)
Security, Privacy, and Data Integrity
Data Security
Protects against loss/corruption ensure recovery
Data Privacy
Ensuring data os protected against unauthorised access
Data Integrity
Ensures consistency, accuracy, and that data is up to date (e.g., validation/verification rules, cascading update/delete).
Why Data Needs To be kept secure
To protect against someone deleting/modifying or stealing it
Why Computer system need to be kept secure
To protect against someone installing malware or damaging the system/accessing data on it
Measures Used to Protect Computer Systems
Two factor authentication
Strong username and password
Prevents unauthorized access
Biometric passwords
Digital Signatures
Use hashing algorithm (hasing) to produce a digest, use key to encrypt.
Firewall
Accepts or rejects incoming/outgoing packets based on criteria/monitors incoming and outgoing traffic
up-to-date anti-Malware (scans files on hard drive for malware)
Anti-spyware (scans computer for spyware)
Backups (data can be restored)
Encryption (converts data into cipher)
Access rights.
** Threats Posed by Internet/Networks
Virus/Malware (malicious software that replicates itself)
Spyware (malicious software secretly recording users data)
Hacking Hackers is an illegal/unauthorised access that is used to delete/damage/collect data.
Phishing REQUIRES USER ACTION (email pretends to be from official body)
Pharming AUTOMATIC (redirects user to a fake website)
Prevention (check URL validity, ensure connection is secure - https)
Security Methods to Protect Security of Data
Access Rights
Encryption (data is converted into cipher text (data is encoded)
Data Integrity
Veriffcation (checks data match the original)
Why data might still be incorrect?
Parity Check (used during transfer)
Checksum (used during transfer)
Ethics and Ownership
Benefits of Joining an Ethical Body e.g BCS, IEEE
Reasons to Act Ethically
How to Act in Best Interest of Client
How to Act Ethically
Being Unethical (Not acting in the best interest of…)
Copyright(protects against unauthorised reproduction of work)
Preventing Illegal Copies(encryption,use product key,compile source code)
Software Licensing
Free Software Foundation & Open Source Initiative
Reason for an open source license
Reasons against an open source license
Shareware
Commercial Software
Applications of Al
Police identifying wanted people (image/facial recognition)
Natural language interfaces( speech recognition)
Self driving cars
Game playing Models characters in computer games (allows comp characters to react according to player's movements)
Social impacts
Economic Impacts
Databases
** Drawbacks limitations of a file-based approach
Advantages of a relational database (compared to file-based approach)
Entity(object which data can be stored about),Field(column/attribute in a table),Tuple(record) a single row of data in a table (about one instance of an object)
Primary Key(unique attribute),Candidate key,Secondary Key(candidate that has not been chosen as primary keys),Foreign Key(a field in one table that links to a primary key in another)
Importance of referential integrity
Normalisation
1NF,2NF,3NF
1NF to 1NF(remove identify repeating groups of attributes)
1NF to 2NF (remove any partial key dependencies)
2NF to 3NF(remove any non -key dependencies)
DB Management Systems (DBMS) - Provides data management
Data Dictionary Contents(metadata about // data abt data in a database). -Table Name
-Field Name - Date Type -Type of validation and Validation Rules.
Logical Scheme
Security in DBMS
different user being able to see different database software tools that process and executes queries written in SQL
DDL and DML
Provides a developer interface
DDL statements are always end with a semicolon!!!