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:

3.1.5 Memory Types

RAM vs ROM:

Static RAM vs Dynamic RAM:

PROM vs EPROM vs EEPROM:

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

OR Gate:

• Output is HIGH if ANY input is HIGH
• Symbol: A + B or A OR B

NOT Gate (Inverter):

• Output is opposite of input
• Symbol: A or NOT A

3.2.2 NAND and NOR Gates

NAND Gate:

• Opposite of AND (NOT-AND)
• Symbol: A · B

NOR Gate:

• Opposite of OR (NOT-OR)
• Symbol: A + B

3.2.3 XOR Gate

XOR (Exclusive OR):

• Output is HIGH if inputs are DIFFERENT
• Symbol: A ⊕ B

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