# [Concepts] Paper 1
# CHAPTER 1: INFORMATION REPRESENTATION
## 1.1 DATA REPRESENTATION
### 1.1.1 Fundamental Characteristics of Number Systems
Every number system has two fundamental characteristics:
1. **Base (Radix)**: The number of different digits that a system can use to represent numbers
2. **Place Value**: The specific value of a digit based on its position within a number
### 1.1.2 Denary (Decimal) System - Base 10
- Uses digits 0-9
- Each position represents powers of 10 (10⁰, 10¹, 10², etc.)
- Example: 3,567 = (3 × 10³) + (5 × 10²) + (6 × 10¹) + (7 × 10⁰)
### 1.1.3 Binary System - Base 2
**Key Points:**
- Uses only two digits: 0 and 1
- Each bit (binary digit) represents a power of 2
- All data and characters in computers are represented in binary
**Binary Place Values:**
<TEXT>
128 | 64 | 32 | 16 | 8 | 4 | 2 | 1
2⁷ 2⁶ 2⁵ 2⁴ 2³ 2² 2¹ 2⁰
**Example - Converting Denary to Binary:**
- Denary 65 in binary: 01000001
- Calculation: 64 + 1 = 65
**Example - Converting Binary to Denary:**
- Binary 01000001 = 64 + 1 = 65
### 1.1.4 Binary Prefixes vs Decimal Prefixes
It is crucial to understand the difference between binary prefixes (based on powers of 2) and decimal prefixes (based on powers of 10):
Denary Prefix
Factor
Value
Binary Prefix
Factor
Value
kilo- (k)
×10³
1,000
kibi- (Ki)
×2¹⁰
1,024
mega- (M)
×10⁶
1,000,000
mebi- (Mi)
×2²⁰
1,048,576
giga- (G)
×10⁹
1,000,000,000
gibi- (Gi)
×2³⁰
1,073,741,824
tera- (T)
×10¹²
1,000,000,000,000
tebi- (Ti)
×2⁴⁰
1,099,511,627,776
**Important:** Always use the correct prefix:
- Computer storage uses binary prefixes (KiB, MiB, GiB, TiB)
- Data transfer rates often use decimal prefixes (kbps, Mbps, Gbps)
### 1.1.5 Binary Coded Decimal (BCD)
**Definition:** Binary representation where each individual denary digit is represented by a sequence of 4 bits (nibble).
**Characteristics:**
- Each nibble can represent denary digits 0-9
- Uses only specific 4-bit patterns (0000 to 1001)
- The patterns 1010 to 1111 are not used in BCD
**Example - Converting 429 to BCD:**
<TEXT>
4 = 0100
2 = 0010
9 = 1001
Therefore, 429 in BCD = 0100 0010 1001
**Practical Applications:**
- Electronic devices displaying numbers (calculators)
- Accurately measuring decimal fractions
- Electronically coding denary numbers
### 1.1.6 Two's Complement Representation
Two's complement is used to represent negative numbers in binary.
**Converting Negative Denary to Binary (Example: -42):**
**Step 1:** Find binary equivalent (ignoring sign)
<TEXT>
42 = 00101010 (8-bit representation)
**Step 2:** Convert to one's complement (flip all bits)
<TEXT>
00101010 → 11010101
**Step 3:** Add 1 to get two's complement
<TEXT>
11010101 + 1 = 11010110
**Converting Binary Two's Complement to Denary (Example: 11010110):**
**Step 1:** Flip all bits
<TEXT>
11010110 → 00101001
**Step 2:** Add 1
<TEXT>
00101001 + 1 = 00101010
**Step 3:** Convert to denary and apply negative sign
<TEXT>
00101010 = 42
Therefore: -42
**Range in 8-bit Two's Complement:**
- Maximum positive: +127 (01111111)
- Maximum negative: -128 (10000000)
**Overflow:**
- Occurs when the result of an arithmetic operation is too large/small to fit in the allocated bits
- Example: Adding 127 + 1 in 8-bit gives -128 (overflow)
### 1.1.7 Hexadecimal System - Base 16
**Characteristics:**
- Uses digits 0-9 and letters A-F
- A=10, B=11, C=12, D=13, E=14, F=15
**Converting Denary to Hexadecimal:** Example: 165 to Hex
<TEXT>
165 ÷ 16 = 10 remainder 5
10 = A
Therefore: 165 = A5 (hex)
**Converting Hexadecimal to Denary:** Example: A5 to Denary
<TEXT>
A5 = (10 × 16) + (5 × 1) = 160 + 5 = 165
**Practical Applications:**
- Defining colours in HTML (#FF0000 = red)
- Defining MAC addresses
- Assembly languages and machine code
- Debugging via memory dumps
### 1.1.8 Character Sets and Encoding
**Definition:** A character set is a collection of characters that can be represented using binary codes. It typically includes upper and lower case letters, number digits, punctuation marks, and other characters.
**Character Encoding Standards:**
Standard
Description
Bits per Character
Characters
ASCII
American Standard Code for Information Interchange
7 bits
128
Extended ASCII
Extension of ASCII
8 bits
256
Unicode
Superset of ASCII and extended ASCII
16 or 32 bits
65,536+
**ASCII:**
- Only supports English alphabet
- 7 bits = 128 possible characters
- Includes control characters (0-31), printable characters (32-126)
**Extended ASCII:**
- 8 bits = 256 possible characters
- Includes most European languages' alphabets
- Still limited for global languages
**Unicode:**
- Modern international standard
- Supports all global languages
- UTF-8 uses 1-4 bytes per character
- Backward compatible with ASCII
---
## 1.2 MULTIMEDIA - GRAPHICS AND SOUND
### 1.2.1 Bitmap Images
**Definition:** Bitmap images are created by assigning a solid colour to each pixel using bit patterns. The image is represented as a grid of pixels, where each pixel's colour is encoded using binary values.
**Key Terms:**
- **Pixel:** The smallest picture element whose colour can be accurately represented by binary code
- **File Header:** Contains metadata including image size, number of colours, etc.
**Image Resolution:**
- Definition: The number of pixels that make up an image
- Example: 4096 × 3192 pixels
- Effect: Higher resolution results in sharper, more detailed images
**Screen Resolution:**
- Definition: The number of pixels that can be viewed horizontally and vertically on a device's screen
- Example: 1680 × 1080 pixels
**Colour Depth:**
- Definition: The number of bits used to represent the colour of a single pixel
- Formula: If n bits are used, there are 2ⁿ colours per pixel
- Example: 16-colour bitmap = 4 bits per pixel (2⁴ = 16)
- Effect: Increasing colour depth improves colour quality but increases file size
**File Size Calculation:**
<TEXT>
File Size = Number of Pixels × Colour Depth
**Example Calculation:**
<TEXT>
Image: 1024 × 768 pixels, 24-bit colour
Number of Pixels = 1024 × 768 = 786,432
Colour Depth = 24 bits
File Size = 786,432 × 24 = 18,874,368 bits
= 18,874,368 ÷ 8 = 2,359,296 bytes
≈ 2.36 MB
**Applications:**
- Scanned images
- Digital photographs
- Computer screen displays
- Small file sizes and easy manipulation when needed
### 1.2.2 Vector Graphics
**Definition:** Made up of drawing objects (mathematically defined constructs like rectangles, lines, circles, curves).
**Components:**
- **Drawing List:** A set of commands defining the vector
- **Properties:** Basic geometric data determining shape and appearance
- **Encoding:** Data is encoded using mathematical formulas
**Advantages over Bitmap:**
- Objects can be resized without losing quality
- Scalability is the key benefit
- Smaller file sizes for simple images
- Can be enlarged infinitely without pixelation
**Disadvantages:**
- Cannot represent complex images like photographs
- More complex to create
**Applications:**
- Company logos
- Architectural drawings
- Icons and symbols
- Fonts (TrueType, PostScript)
### 1.2.3 Sound Representation
**Analogue vs Digital:**
Analogue
Digital
Continuous electrical signals
Discrete electrical signals
Infinite detail
Finite representation
Cannot be stored directly
Can be stored in binary
**Sound as Analogue Data:**
- Sound consists of vibrations through a medium
- Inherently analogue due to infinite detail variation
**Conversion Process (Analogue to Digital):**
1. **Sampling:** The sound wave's amplitude is measured at set time intervals
2. **Quantization:** Each sample is assigned a binary value
3. **Encoding:** Binary values are stored
**Key Terms:**
- **Sampling Rate:** Number of samples taken per unit of time (measured in Hz)
- Effect: Increasing sampling rate improves accuracy but increases file size
- CD quality: 44,100 Hz
- **Sampling Resolution:** Number of bits used to encode each sample
- Effect: Increasing resolution improves accuracy but increases file size
- CD quality: 16 bits
- **Bit Rate:** Number of bits used to store 1 second of sound
- Formula: Bit Rate = Sampling Rate × Sampling Resolution
- Example: 44,100 × 16 = 705,600 bps (approximately 706 Kbps)
---
## 1.3 COMPRESSION
### 1.3.1 Need for Compression
**Definition:** Compression is the process of reducing file size without significant loss in quality.
**Benefits:**
- Reduced storage requirements
- Faster data transfer (uses less bandwidth)
- Reduced time needed to search for data
### 1.3.2 Lossless Compression
**Definition:** A type of compression that allows original data to be perfectly reconstructed from the compressed file.
**Key Feature:**
- Uses some form of replacement (substitution)
- No data is permanently deleted
**Examples:**
- PNG images (for graphics with sharp edges)
- ZIP files
- Text file compression
- Database records
- Run-Length Encoding (RLE)
**Run-Length Encoding (RLE):**
**Definition:** A form of lossless compression used for compressing text files and bitmap images.
**Mechanism:**
- Reduces file size by encoding sequences of adjacent, identical elements
- Encodes as two values: run count and run value
**Example:** Original: AAAAAAABBBBBCCCCCC Compressed: 7A5B6C
**Example - Bitmap:** Original row: White White White White White Black Black Compressed: 5W2B
**Applications:**
- Simple graphics with large areas of same colour
- Database records with repeated values
### 1.3.3 Lossy Compression
**Definition:** A type of compression that irreversibly eliminates unnecessary data.
**Characteristics:**
- File accuracy/quality is lower than lossless
- File size is significantly reduced (often to about 10% of lossless size)
- Some original data is permanently lost
**Examples:**
- MP3 (sound files)
- JPEG (images)
- MP4 (video files)
**Mechanism in Sound Files (MP3):**
- **Perceptual Coding:** Removes parts of the sound that are less audible or discernible to human hearing
- Removes frequencies outside human hearing range
- Removes subtle volume differences
**Mechanism in Images (JPEG):**
- Removes high-frequency details
- Uses mathematical approximations
- Reduces colour precision in less important areas
**When to Use Lossy vs Lossless:**
Lossless
Lossy
Text documents
Photography
Database files
Video streaming
Program files
Music (streaming)
Spreadsheets
Web graphics (where size matters)
---
# CHAPTER 2: COMMUNICATION AND NETWORKING
## 2.1 NETWORKS INCLUDING THE INTERNET2.1.1 Introduction to Networks
**Definition:** Networking devices are interconnected devices that enable fast data transmission within a network.
**Benefits of Networking:**
1. **File Sharing:** Easily share data between different interconnected devices
2. **Resource Sharing:** Use network-connected output devices like printers or share software
3. **Higher Storage:** Files can be stored in network-connected storage mediums
4. **Communication:** Email and messaging between users
5. **Centralized Management:** Easier to backup and secure data
### 2.1.2 Types of Networks
**LAN (Local Area Network):**
Characteristic
Description
Geographic Area
Small area, often within the same building
Ownership
Private ownership
Transmission Medium
Twisted pair cables, coaxial cables, or Wi-Fi
Data Transfer Rate
Higher (100 Mbps to 10 Gbps)
Congestion
Less congestion
Setup Cost
Lower initial cost
**WAN (Wide Area Network):**
Characteristic
Description
Geographic Area
Large area - city, country, or globally
Ownership
Private or public ownership
Transmission Medium
PSTN, satellite links, leased lines
Data Transfer Rate
Lower
Congestion
Higher congestion
Setup Cost
Higher initial cost
### 2.1.3 Network Models
**Client-Server Model:**
- A dedicated server provides applications (administration of users, security, and resources)
- Clients access resources from the server
- Server manages all central functions
**Server Types:**
- Print Server: Manages print jobs from client computers
- File Sharing Server: Clients access software and user data files stored on the server
- Proxy Server: Acts as intermediary for internet requests
- Email Server: For sending, receiving, and storing emails
- Database Server: Manages DBMS
- Domain Controller Server: Manages user accounts (IDs & passwords)
**Client-Server Login Process:**
1. Client sends login request to server
2. Server processes request
3. Server grants access if user ID & password are recognized
**Thin Clients vs Thick Clients:**
Thin Clients
Thick Clients
Runs solely on server resources
Processes most application locally
No local storage
Has local storage and processing power
Smaller purchase cost
More expensive
Requires constant server connection
Can work offline
Improved security
More vulnerable to unauthorized software
**Peer-to-Peer (P2P) Network:**
- Decentralized network
- Each computer operates independently as a 'peer'
- Acts as both client and server
- No central server required
- Common in file sharing applications (BitTorrent)
**Comparison:**
Feature
Client-Server
Peer-to-Peer
Centralized backup
Yes
No
Initial setup cost
Higher
Lower
Network traffic
Higher (goes through server)
Lower (direct)
Security
Better (centralized control)
Weaker
Reliability
Server failure affects all
Peer failure affects one
### 2.1.4 Network Topologies
**Bus Topology:**
- Single line (bus) connects all devices
- Terminators at each end
- All computers can read data being sent between any two computers
- **Disadvantage:** Unsuitable for heavy traffic due to frequent collisions
- Uses CSMA/CD for collision detection
**Star Topology:**
- Central server/switch with all computers connected via dedicated connections
- Server can send packets to different devices simultaneously
- No collisions possible
- Most common in modern networks
**Mesh Topology:**
- Every device (node) is directly interconnected with all other devices
- Commonly used for wireless networks
- High redundancy (if one path fails, another can be used)
**Hybrid Topology:**
- Combination of two or more topologies
- Example: Connection between two or more LANs of different topologies
### 2.1.5 Transmission Media
**Wired Networks:**
**Copper Cable:**
Advantages
Disadvantages
Less expensive
Doesn't perform well with small charges
Easier to install
Affected by electromagnetic interference
Flexible
Signal degradation over distance
Easy to make terminations
**Fibre-Optic Cable:**
Advantages
Disadvantages
Greater bandwidth
Needs expensive optical transmitters/receivers
Improved security
More difficult to install
Lightweight
Less signal boosting required
Used in long-distance communications
Immune to electromagnetic interference
**Wireless Networks:**
Type
Advantages
Disadvantages
Radio Waves
Can travel over large distances; inexpensive
Low frequency = less data; affected by interference
Microwaves
Larger bandwidth
Physical obstacles interfere; expensive towers
Satellites
Cost-effective for long-distance
Expensive setup; susceptible to interference
### 2.1.6 Ethernet
**Definition:** The most common wired medium for data transmission in LANs or WANs.
**CSMA/CD (Carrier Sense Multiple Access with Collision Detection):**
**Process:**
1. Device checks if channel is busy before transmitting
2. If busy, device waits a random time before retrying
3. During transmission, device listens for other transmissions
4. If collision occurs, transmission is aborted
5. Both devices wait random times before retrying
### 2.1.7 Bit Streaming
**Definition:** Sequence of digital signals (bits) transferred over a communication path at high speeds.
**Types:**
**Real-time Streaming:**
- Live events captured and transmitted directly
- Cannot be paused, fast-forwarded, etc.
- Example: Live TV, video conferencing
**On-demand Streaming:**
- Pre-existing files are converted and streamed as requested
- Can be paused, fast-forwarded, etc.
- Example: YouTube, Netflix
**Importance of High Broadband Speed:**
- User has to download and display bits simultaneously
- Higher quality media requires faster speeds
- Real-time streaming needs higher speeds for simultaneous data requests
### 2.1.8 Cloud Computing
**Definition:** On-demand provision of computing services over the internet.
**Services:**
- **Infrastructure:** Storage capacity and higher processing power
- **Platform:** Software, testing & debugging resources
**Public Cloud vs Private Cloud:**
Feature
Public Cloud
Private Cloud
Access
Third-party providers, shared among multiple users
Single organization, exclusive access
Management
Managed by service providers
Can be managed internally or outsourced
**Benefits:**
- Less technical knowledge required
- Easy to implement
- Flexibility to scale with growth
**Drawbacks:**
- Cannot access resources if bandwidth issues
- Poor data privacy (potential data leakage in multi-tenant architecture)
### 2.1.9 Internet and World Wide Web
**Internet:**
- Massive, open network of networks
- Uses TCP/IP protocol
- IP addresses identify devices
**World Wide Web (WWW):**
- Collection of web pages stored on websites
- Uses protocols (HTTP/HTTPS) to transmit data
### 2.1.10 Network Hardware
Device
Function
**Router**
Connects two networks; translates IP addresses; acts as gateway and firewall
**Switch**
Connects devices in LAN; broadcasts to all devices simultaneously
**Server**
Provides specific functions for computers in the network
**NIC (Network Interface Card)**
Provides unique MAC address for wired connection
**WNIC (Wireless NIC)**
Provides unique address for WiFi connection
**WAP (Wireless Access Point)**
Allows devices to connect via WiFi
**Bridge**
Connects two LANs using same protocol
**Repeater**
Regenerates signal to prevent attenuation
**Modem**
Converts digital to analogue signals for telephone lines
### 2.1.11 IP Addressing
**IPv4:**
- 32-bit address
- 4 blocks separated by dots (e.g., 192.168.1.1)
- Each block: 0-255
**IPv6:**
- 128-bit address
- 8 blocks separated by colons
- Each block: 4 hex values (0000-FFFF)
- Can be shortened by removing consecutive zero blocks
**IP Address Structure:**
- **Network Identifier (NetID):** Identifies the network
- **Host Identifier (HostID):** Identifies the device within the network
**Subnetting:**
- Practice of dividing a network into two or more sub-networks
- IP address broken into: NetID + SubnetID + HostID
**Public vs Private IP:**
- Public IP: Provided by ISP; unique; accessible from internet
- Private IP: Issued by LAN's router; only accessible within LAN
- NAT (Network Address Translation) required for private IPs to access internet
**Static vs Dynamic:**
- Static: Never changes; used for servers, VPNs
- Dynamic: Changes regularly; more secure; used for general users
### 2.1.12 DNS (Domain Name Service)
**Definition:** A naming system that maps domain names to IP addresses.
**Function:**
- Hierarchy of DNS servers
- Database of URLs and corresponding IP addresses
- Translates human-readable domain names to IP addresses
# CHAPTER 3: HARDWARE AND COMPUTER COMPONENTS
## 3.1 COMPUTERS AND THEIR COMPONENTS
### 3.1.1 General-Purpose Computer System
A general-purpose computer system comprises:
1. **Processor (CPU):** Executes instructions
2. **Memory:** Stores data and instructions
3. **Input/Output (I/O):** Interfaces with external world
### 3.1.2 Essential Features of a Computer
**Input:**
- Takes in data from the outside world
- Devices: keyboard, mouse, scanner, microphone
**Output:**
- Displays data for human understanding
- Devices: monitor, printer, speaker
**Primary Storage (Memory):**
- Main memory storing critical program instructions and data
- RAM (Random Access Memory)
- Volatile (loses data when power off)
**Secondary Storage:**
- Non-volatile storage for data
- Examples: hard disk, SSD, USB flash drive
**Removable Secondary Storage:**
- File backup and archives
- Portable transfer of files
### 3.1.3 Embedded Systems
**Definition:** Miniature computer systems (microprocessors) that are often part of a larger system.
**Characteristics:**
- Perform few specific functions
- Not general-purpose computers
- No moving parts (more reliable)
**Advantages:**
- Reliable (no moving parts)
- Require less power
- Cheap to mass-produce
**Disadvantages:**
- Difficult to program (no interface)
- Expensive expert help needed for repair
### 3.1.4 Hardware Device Operations
**Laser Printer:**
1. Laser beam and rotating mirrors draw image on photosensitive drum
2. Image converted to electric charge
3. Charged toner attracts to image
4. Electrostatic-charged paper rolls against drum
5. Charge pulls toner onto paper
6. Heat in fuser fuses toner to paper
**3D Printer:**
1. Starts with saved digital file (blueprint)
2. Object built by adding layers of material (polymer resin)
3. Object cured (hardened by UV light)
**Microphone:**
1. Sound waves enter and cause diaphragm vibrations
2. Vibrations cause coil to move past magnetic core
3. Electrical current generated
4. Current digitized
**Speaker:**
1. Takes electrical signals
2. Voice coil generates electromagnetic field
3. Change in audio signal changes current direction
4. Electromagnet attracted/repelled to permanent magnet
5. Diaphragm vibrates, creating sound waves
**Magnetic Hard Disk:**
1. Platters covered with magnetizable material
2. Mounted on central spindle, rotated at high speed
3. Surface divided into concentric tracks & sectors
4. Data encoded as magnetic patterns
5. Read/write heads access data
**Solid State (Flash) Memory:**
- Uses NAND-based flash memory
- Grid of columns & rows with 2 transistors at each intersection
- Floating gate stores electrons (represents 0 or 1)
- Control gate controls charge flow
**Optical Disc Reader/Writer:**
1. Disc surface has reflective metal layer
2. Spun at high speed
3. Laser beam reads/writes
4. Tracks have amorphous and crystalline states
5. Different states encode bit patterns
**Touchscreen:**
Type
Description
Resistive
Two charged plates; pressure causes contact
Capacitive
Materials that store electric charge; touch transfers charge
### 3.1.5 Memory Types
**RAM vs ROM:**
Feature
RAM
ROM
Volatility
Volatile (loses data when power off)
Non-volatile
Read/Write
Can be read and written
Can only be read
Use
Stores currently executing program
Stores OS kernel, boot-up instructions
**Static RAM vs Dynamic RAM:**
Feature
SRAM
DRAM
Refresh
Doesn't need to refresh
Must be refreshed
Speed
Faster access time
Slower access time
Power
Uses less power
Needs higher power
Cost
More expensive (complex circuitry)
Less expensive
Structure
Each bit stored in flip-flop
Each bit stored as charge in capacitor
Density
Lower data density
Higher data density
Use
Cache memory
Main memory
**PROM vs EPROM vs EEPROM:**
Type
Description
Erasure Method
PROM
Programmable once after creation
Cannot be erased
EPROM
Can be reprogrammed
UV light exposure
EEPROM
Can be reprogrammed
Electrical signal
### 3.1.6 Monitoring and Control Systems
**Monitoring System:**
- Monitors state external to computer
- No changes made to environment
- No feedback required
**Control System:**
- Regulates behaviour of other devices/systems
- **Event-driven:** Responds to specific events
- **Time-driven:** Takes action at specific times
**Components:**
- **Sensor:** Measures analogue property, transmits to processing unit
- **Actuator:** Switches on/off heavy appliances (heater, fan)
- **ADC:** Converts analogue signals to digital
- **Transmission cable:** Transfers signals
**Feedback Systems:**
- Output affects input of sensors
- Ensures system operates within criteria
- Enables automatic adjustment of conditions
---
## 3.2 LOGIC GATES AND LOGIC CIRCUITS
### 3.2.1 Basic Logic Gates
**AND Gate:**
- Output is HIGH only if ALL inputs are HIGH
- Symbol: A · B or A AND B
A
B
Output
0
0
0
0
1
0
1
0
0
1
1
1
**OR Gate:**
- Output is HIGH if ANY input is HIGH
- Symbol: A + B or A OR B
A
B
Output
0
0
0
0
1
1
1
0
1
1
1
1
**NOT Gate (Inverter):**
- Output is opposite of input
- Symbol: A or NOT A
A
Output
0
1
1
0
### 3.2.2 NAND and NOR Gates
**NAND Gate:**
- Opposite of AND (NOT-AND)
- Symbol: A · B
A
B
Output
0
0
1
0
1
1
1
0
1
1
1
0
**NOR Gate:**
- Opposite of OR (NOT-OR)
- Symbol: A + B
A
B
Output
0
0
1
0
1
0
1
0
0
1
1
0
### 3.2.3 XOR Gate
**XOR (Exclusive OR):**
- Output is HIGH if inputs are DIFFERENT
- Symbol: A ⊕ B
A
B
Output
0
0
0
0
1
1
1
0
1
1
1
0
### 3.2.4 Constructing Circuits from Truth Tables
**Process:**
1. Identify required output for each input combination
2. Identify the logic expression
3. Design the circuit using appropriate gates
4. Test with truth table
# CHAPTER 4: PROCESSOR FUNDAMENTALS
## 4.1 CENTRAL PROCESSING UNIT (CPU) ARCHITECTURE
### 4.1.1 Von Neumann Model
**Key Concept:**
- Data and programs are indistinguishable
- Can use the same memory for both
- Uses a single processor
- Follows fetch-decode-execute cycle
**Components:**
- Processor (CPU)
- Memory (for data and instructions)
- Input/Output devices
### 4.1.2 Registers
**Definition:** The smallest unit of storage in a microprocessor; allows fast data transfer.
**General Purpose Registers:**
- Used to temporarily store data values
- Can be used by assembly language instructions
- Example: Accumulator (ACC)
**Special Purpose Registers:**
Register
Function
**PC (Program Counter)**
Holds address of next instruction
**MDR (Memory Data Register)**
Holds data fetched from memory
**MAR (Memory Address Register)**
Holds address of memory cell to access
**ACC (Accumulator)**
Holds values processed by ALU
**IX (Index Register)**
Stores number to modify address
**CIR (Current Instruction Register)**
Holds current instruction for decoding
**Status Register**
Holds results of comparisons, arithmetic flags
### 4.1.3 CPU Components
**ALU (Arithmetic and Logic Unit):**
- Part of processor that processes instructions
- Performs arithmetic operations (add, subtract, multiply, divide)
- Performs logical operations (AND, OR, NOT)
**Control Unit (CU):**
- Fetches instructions from memory
- Decodes instructions
- Synchronizes operations
- Sends signals to memory, ALU, and I/O devices
**System Clock:**
- Timing device connected to processor
- Synchronizes all components
- Generates clock pulses
**IAS (Immediate Access Store):**
- Memory unit the processor can directly access
### 4.1.4 Buses
**Definition:** Set of parallel wires allowing data transfer between components.
**Data Bus:**
- Bidirectional
- Carries data between processor, memory, and I/O devices
**Address Bus:**
- Unidirectional
- Carries memory address from processor to MAR
**Control Bus:**
- Bidirectional
- Transmits control signals from CU
- Ensures components don't conflict
### 4.1.5 Performance Factors
**Clock Speed:**
- Number of pulses the clock sends in a given time
- Usually measured in GHz
- Higher clock speed = more cycles per second = faster execution
- Limitation: Heat generation at high speeds
**Bus Width:**
- Number of bits that can be transferred simultaneously
- Wider bus = more bits transferred at once = faster processing
**Cache Memory:**
- Stores commonly used instructions
- Larger cache = more instructions stored = less waiting = better performance
**Number of Cores:**
- Multi-core processors have multiple processing units
- Each core can process different instructions simultaneously
- Improves performance through parallel processing
### 4.1.6 Ports
Port Type
Description
**USB**
Connects input and output devices
**HDMI**
High-definition video and audio output
**VGA**
Video output only (older displays)
### 4.1.7 Fetch-Execute Cycle
**Fetch Stage:**
1. PC holds address of next instruction
2. Address copied to MAR
3. PC incremented
4. Instruction loaded to MDR from address in MAR
5. Instruction from MDR loaded to CIR
**Decode Stage:**
- Opcode and operand parts identified
**Execute Stage:**
- Control unit executes instruction
- Return to start
**Register Transfer Notation (RTN):**
<TEXT>
MAR ← \[PC\]
PC ← \[PC\] + 1
MDR ← \[\[MAR\]\]
CIR ← \[MDR\]
Decode
Execute
Return to start
### 4.1.8 Interrupts
**Definition:** A signal from a program seeking the processor's attention.
**ISR (Interrupt Service Routine):**
- Handles the interrupt
- Different ISRs for different sources
**Interrupt Handling Process:**
1. Processor checks interrupt register at end of F-E cycle
2. If interrupt flag is set, source detected
3. If low priority, interrupt disabled
4. If high priority:
- Save register contents to stack
- Load PC with ISR address
- Execute ISR
- Restore registers from stack
- Continue interrupted program
---
## 4.2 ASSEMBLY LANGUAGE
### 4.2.1 Introduction
**Assembly Language:**
- Low-level programming language
- Instructions consist of opcode and operand
**Machine Code:**
- Binary code the processor executes directly
- One-to-one relationship with assembly language
**Assembler:**
- Software that translates assembly language to machine code
- Replaces mnemonics and labels with binary values
### 4.2.2 Assembler Types
**One-Pass Assembler:**
- Converts source code in one sweep
- Cannot handle forward referencing
**Two-Pass Assembler:**
**Pass 1:**
- Creates symbol table
- Enters symbolic addresses and labels
**Pass 2:**
- Translates to machine code using table
- Reports errors
### 4.2.3 Addressing Modes
Mode
Description
**Immediate**
Data is the actual value (e.g., LDM #n)
**Direct**
Load contents at given address (e.g., LDD address)
**Indirect**
Address to use is at given address (e.g., LDI address)
**Indexed**
Address = given address + contents of IX (e.g., LDX address)
**Relative**
Next instruction is offset from current instruction
### 4.2.4 Instruction Types
**Data Movement:**
- LDM#: Load immediate
- LDD: Load direct
- LDI: Load indirect
- LDX: Load indexed
- STO: Store
**Arithmetic:**
- ADD: Add to accumulator
- SUB: Subtract from accumulator
- INC: Increment
- DEC: Decrement
**Comparing:**
- CMP: Compare with contents at address
- CMP#: Compare with immediate value
**Conditional Jumps:**
- JPE: Jump if equal (compare TRUE)
- JPN: Jump if not equal (compare FALSE)
**Unconditional Jumps:**
- JMP: Jump to address
**I/O:**
- IN: Input character
- OUT: Output character
**End:**
- END: Return control to OS
---
## 4.3 BIT MANIPULATION
### 4.3.1 Binary Shifts
**Left Shift (LSL #n):**
- Bits shifted left
- Multiplies by 2ⁿ
- Zeros fill vacated positions
**Right Shift (LSR #n):**
- Bits shifted right
- Divides by 2ⁿ
- Zeros fill vacated positions
**Arithmetic Shift:**
- Used for signed integers
- Sign bit (MSB) maintained
**Cyclic Shift:**
- Bit removed from one end added to other end
### 4.3.2 Bit Masking
**Purpose:** Each bit can represent an individual flag. By manipulating bits, flags can be operated upon.
**Operations:**
**Masking to 1:**
- Use OR operation with 1
**Masking to 0:**
- Use AND operation with 0
**Testing Bits:**
- Use AND to mask bits
- Compare result with pattern
**Practical Applications:**
- Setting individual bit positions
- Testing specific bits
- Checking patterns
# CHAPTER 5: SYSTEM SOFTWARE
## 5.1 OPERATING SYSTEMS
### 5.1.1 Need for Operating System
**Definition:** A set of programs designed to run in the background on a computer system.
**Functions:**
- Controls operation of computer system
- Provides user interface
- Controls how computer responds to requests
- Controls how hardware communicates
- Provides environment for application software
**Why OS is Essential:**
- Hardware is unusable without OS
- Acts as interface between user and hardware
- Manages communication between components
### 5.1.2 Key Management Tasks
**Memory Management:**
- Memory protection (ensures programs don't use same memory)
- Paging (uses virtual memory)
- Memory allocation
**File Management:**
- Provides file naming conventions
- Maintains directory structure
- Allocates space to files
- File access control
**Security Management:**
- Provides usernames & passwords
- Ensures data privacy
- Prevents unauthorized access
- Carries out automatic backup
**Hardware Management:**
- Installation of driver software
- Controls access to peripherals
- Handles interrupts from devices
**Process Management:**
- Enables multiprogramming and multitasking
- Resolves conflicts when processes need same resource
- Methods: Round-robin, priority scheduling
### 5.1.3 Utility Software
**Disk Formatter:**
- Prepares hard disk for data storage
- Deletes existing data
- Creates sectors and tracks
**Virus Checker:**
- Checks for viruses
- Removes viruses found
- Monitors incoming/outgoing files
**Defragmentation Software:**
- Reorganizes files to contiguous sectors
- Reduces read/write head movements
- Improves performance
**Disk Repair Software:**
- Visualizes disk space usage
- Reports errors (bad sectors)
- Attempts to fix issues
**File Compression:**
- Reduces file size
- Removes redundant data
- Improves storage efficiency
**Backup Software:**
- Makes copies of files
- Stores on different medium
- Provides synchronization between devices
### 5.1.4 Program Libraries
**Definition:** Pre-written code that can be linked to software under development.
**Benefits:**
- Saves time (less code to write)
- Smaller testing time (pre-tested)
- Complex algorithms available without understanding implementation
**DLL (Dynamic Link Library):**
- Shared library file containing code and data
- Loaded to memory only when required
- Available to several applications simultaneously
- Reduces .EXE file size
---
## 5.2 LANGUAGE TRANSLATORS
### 5.2.1 Assembler
**Purpose:** Translates assembly language to machine code (binary).
**Characteristics:**
- One-to-one relationship with machine code
- Simple translation process
### 5.2.2 Compiler vs Interpreter
Feature
Compiler
Interpreter
Translation
Translates entire program before execution
Translates line-by-line
Output
Creates .exe file
No .exe created
Execution
Faster (already compiled)
Slower (translates each time)
Error Reporting
All errors at end
Stops at first error
Development
Used when development complete
Used during development
Debugging
Difficult (all errors at end)
Easier (stops at error)
### 5.2.3 Two-Step Translation (Java)
**Process:**
1. Java compiler translates source code to bytecode
2. Java Virtual Machine (JVM) interprets bytecode to machine code
**Benefits:**
- Platform independence (write once, run anywhere)
### 5.2.4 IDE Features
**Coding Features:**
- Context-sensitive prompts
- Variable highlighting (undeclared/unassigned)
- Autocomplete
**Error Detection:**
- Dynamic syntax checking
- Type checking
- Parameter checking
**Presentation:**
- Prettyprint (automatic indentation, colour-coding)
- Expand and collapse code blocks
**Debugging:**
- Single stepping (execute line-by-line)
- Breakpoints (pause at specific line)
- Variables/expressions report window
# CHAPTER 6: SECURITY, PRIVACY AND DATA INTEGRITY
## 6.1 DATA SECURITY
### 6.1.1 Definitions
**Data Security:**
- Ensuring data is protected against loss and unauthorized access
- Protection of data on computer system
**Data Integrity:**
- Ensuring data is valid and does not corrupt after transmission
- Data is accurate and reliable
**Data Privacy:**
- Ability to determine what data is shared with third party
### 6.1.2 Threats to Computer and Data Security
**Malware:**
- Software designed to damage computer or network
- **Virus:** Replicates by inserting copy into other software; can crash computer, delete/corrupt data
- **Spyware:** Gathers information about users' activity; monitors online/offline behaviour
**Hacking:**
- Illegal access to computer system
- Obtain confidential data
- Can cause identity theft
- Can delete/corrupt data
**Phishing:**
- Emails attempting to obtain confidential data
- Impersonates legitimate organizations
- Causes identity theft
**Pharming:**
- Redirects users to fake websites
- Appears legitimate
- Gains confidential data
### 6.1.3 Security Measures
**User Accounts and Passwords:**
- Deny unauthorized access
- User-assigned privilege levels
- File access permissions
**Firewalls:**
- Filters information between computer and internet
- Detects illegal connection attempts
- Blocks unauthorized access
**Authentication:**
- Determines if someone is who they claim
- Methods: passwords, digital signatures, biometric scans
**Anti-virus Software:**
- Detects and removes viruses
- Checks files for malicious patterns
- Runs in background
**Anti-spyware Software:**
- Detects and removes spyware
**Encryption:**
- Converts data to code
- Doesn't stop access but makes data meaningless
- Requires decryption to read
**Data Backup:**
- Exact copy of original data
- Stored at different location
- Disk-mirroring: writes to multiple disks simultaneously
### 6.1.4 Data Security vs System Security
Data Security
System Security
Protection of data on system
Protection of computer system
Prevents corruption, unauthorized use
Prevents viruses, hacking
Example: encryption
Example: firewall, passwords
---
## 6.2 DATA INTEGRITY
### 6.2.1 Data Validation
**Definition:** Checks if data entered is valid (sensible).
**Methods:**
Method
Description
**Range Check**
Data must be between set values
**Format Check**
Data must follow correct pattern
**Length Check**
Data must have exact number of characters
**Presence Check**
Checks if data has been entered
**Existence Check**
Data entered must exist in database
**Limit Check**
Value within acceptable min/max
**Check Digit**
Arithmetic result of other digits; verifies accuracy
### 6.2.2 Data Verification
**Definition:** Checks data entered is accurate (correct).
**Data Entry Verification:**
Method
Description
**Visual Check**
Person manually compares original with entered data
**Double Entry**
Enter data twice; compares results
**Data Transfer Verification:**
**Parity Check:**
- Number of 1s in byte must be odd or even
- If parity doesn't match, error detected
- Limitation: Cannot detect 2-bit transposition
**Checksum Check:**
- Data sent as block of bytes
- All bytes added together
- Checksum calculated before and after transmission
- If different, error occurred; block must be resent
# CHAPTER 7: ETHICS AND OWNERSHIP
## 7.1 ETHICS AND OWNERSHIP
### 7.1.1 Ethics
**Definition:** A system of moral principles that guide behaviour based on philosophical views.
**Computer Ethics:**
- Regulates how computing professionals should make decisions
- Professional and social conduct
**Professional Bodies:**
- BCS (British Computer Society)
- IEEE (Institute of Electrical and Electronic Engineers)
- Provide codes of conduct for members
### 7.1.2 Ownership
**Data Ownership:**
- Legal rights and complete control over data
- Can determine who accesses, modifies, shares
**Copyright:**
- Gives creators rights to control use and distribution
- Protects intellectual property
**Need for Legislation:**
- Competitors can steal programming ideas
- Software can be easily copied
- Bootlegging (illegal selling)
### 7.1.3 Software Licensing
Type
Description
**Free Software Foundation**
Users have freedom to run, copy, distribute, study, change, improve; copyleft (modified versions must also be free)
**Open Source Initiative**
Source code available; users can review and redistribute
**Shareware**
Free trial period; payment expected after evaluation
**Commercial**
Requires payment; includes all features
### 7.1.4 Artificial Intelligence (AI)
**Definition:** The ability of computer to perform tasks conventionally associated with human intelligence.
**AI Capabilities:**
- Learn from past mistakes
- Adapt to prevent problems recurring
- Predict what might happen and raise alerts
- Learn to work more efficiently
**AI Applications:**
- Autonomous vehicles
- Machine learning through data sets
- Natural language processing
- Robotics
**AI Impacts:**
Area
Impact
**Social**
Replacement of manual labour; unemployment; increased leisure time
# CHAPTER 8: DATABASE CONCEPTS AND MANAGEMENT
## 8.1 DATABASE CONCEPTS
### 8.1.1 Limitations of File-Based Systems
**Disadvantages:**
- No enforcing control on organization/structure
- Data repeated in different files
- Manual changes required in all files
- Sorting must be done manually or by program
- Data may be in different formats
- Cannot be multi-user (chaotic)
- Security not sophisticated
### 8.1.2 Database Approach
**Database:**
- Collection of non-redundant interrelated data
- Organized for efficient access
**DBMS (Database Management System):**
- Software programs that allow databases to be defined, constructed, and manipulated
### 8.1.3 Relational Database Terminology
Term
Definition
**Entity**
Object/event that can be distinctly identified
**Table**
Contains related entities in rows and columns
**Tuple**
Row/record in relational database
**Attribute**
Field/column in relational database
**Primary Key**
Attribute that uniquely identifies each tuple
**Candidate Key**
Attribute that can potentially be primary key
**Foreign Key**
Attribute that relates two different tables
**Secondary Key**
Candidate key not chosen as primary
**Referential Integrity**
Prevents inconsistent data in relationships
### 8.1.4 Entity-Relationship Diagrams
**Relationships:**
- **One-to-Many:** One record relates to many records
- **One-to-One:** One record relates to one record
- **Many-to-Many:** Many records relate to many records (requires intermediate table)
## 8.2 DATABASE MANAGEMENT SYSTEMS (DBMS)
### 8.2.1 Features of DBMS
**Data Management:**
- Data stored in relational tables
- Secondary storage
**Data Dictionary:**
- List of all files
- Number of records
- Names and types of fields
**Data Modelling:**
- Analysis of data objects
- Identifying relationships
**Logical Schema:**
- Overall view of database
- Entities, attributes, relationships
**Data Integrity:**
- Block copied when changed
- Saved back when done
**Data Security:**
- Password allocation
- Automatic backups
- Access rights control
**Data Change Handling:**
- Exclusive mode (impractical for multiple users)
- Lock all records in table
- Lock current record only
- Warn of simultaneous change
**Deadlock:**
- Two locks at same time
- One user must abort
### 8.2.2 DBMS Tools
**Developer Interface:**
- Creates and manipulates database in SQL
**Query Processor:**
- Handles high-level queries
- Parses, validates, optimizes
- Creates query plan
## 8.3 NORMALIZATION
### 8.3.1 First Normal Form (1NF)
**Requirements:**
- No repeating attributes
- Intersection of each tuple and attribute contains only one value
### 8.3.2 Second Normal Form (2NF)
**Requirements:**
- In 1NF
- Every non-primary key attribute fully dependent on primary key
- Remove incomplete dependencies
### 8.3.3 Third Normal Form (3NF)
**Requirements:**
- In 1NF and 2NF
- All non-key elements fully dependent on primary key
- No inter-dependencies between attributes
### 8.3.4 Many-to-Many Relationships
- Cannot be directly normalized to 3NF
- Must use intermediate table (two-step process)
## 8.4 SQL (STRUCTURED QUERY LANGUAGE)
### 8.4.1 Data Definition Language (DDL)
**CREATE DATABASE:**
<SQL>
CREATEDATABASEdatabase-name
**CREATE TABLE:**
<SQL>
CREATETABLEtable-name (
field1 data-type,
field2 data-type,
...
)
**ALTER TABLE:**
<SQL>
ALTERTABLEtable-nameADD field-namedata-type
**PRIMARY KEY:**
<SQL>
PRIMARY KEY (field)
**FOREIGN KEY:**
<SQL>
FOREIGN KEY (field) REFERENCEStable(field)
### 8.4.2 Data Manipulation Language (DML)
**SELECT (Query):**