# 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:**
TypeDescription
ResistiveTwo charged plates; pressure causes contact
CapacitiveMaterials that store electric charge; touch transfers charge
### 3.1.5 Memory Types **RAM vs ROM:**
FeatureRAMROM
VolatilityVolatile (loses data when power off)Non-volatile
Read/WriteCan be read and writtenCan only be read
UseStores currently executing programStores OS kernel, boot-up instructions
**Static RAM vs Dynamic RAM:**
FeatureSRAMDRAM
RefreshDoesn't need to refreshMust be refreshed
SpeedFaster access timeSlower access time
PowerUses less powerNeeds higher power
CostMore expensive (complex circuitry)Less expensive
StructureEach bit stored in flip-flopEach bit stored as charge in capacitor
DensityLower data densityHigher data density
UseCache memoryMain memory
**PROM vs EPROM vs EEPROM:**
TypeDescriptionErasure Method
PROMProgrammable once after creationCannot be erased
EPROMCan be reprogrammedUV light exposure
EEPROMCan be reprogrammedElectrical 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
ABOutput
000
010
100
111
**OR Gate:** - Output is HIGH if ANY input is HIGH - Symbol: A + B or A OR B
ABOutput
000
011
101
111
**NOT Gate (Inverter):** - Output is opposite of input - Symbol: A or NOT A
AOutput
01
10
### 3.2.2 NAND and NOR Gates **NAND Gate:** - Opposite of AND (NOT-AND) - Symbol: A · B
ABOutput
001
011
101
110
**NOR Gate:** - Opposite of OR (NOT-OR) - Symbol: A + B
ABOutput
001
010
100
110
### 3.2.3 XOR Gate **XOR (Exclusive OR):** - Output is HIGH if inputs are DIFFERENT - Symbol: A ⊕ B
ABOutput
000
011
101
110
### 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