Computer Hardware

System Foundation

1. The Motherboard & System Unit

The Motherboard (also known as the mainboard or system board) is the primary Printed Circuit Board (PCB) that houses and interconnects all essential hardware subsystems of a computer.

Key On-Board Components

CPU Socket: Mechanical connector holding the microprocessor (LGA / PGA format).
Chipset: Micro-controllers regulating data traffic between CPU, RAM, and PCIe peripherals (Southbridge/PCH).
BIOS/UEFI Chip: Non-volatile ROM containing low-level firmware to initialize hardware during POST (Power-On Self-Test).
CMOS Battery (CR2032): Small lithium coin cell maintaining system clock, date, and hardware settings when power is off.
Expansion Slots (PCIe): High-speed serial expansion buses for dedicated Graphics Cards (GPU ×16), sound cards, and Wi-Fi adapters.
RAM DIMM Slots: Sockets holding Dual In-line Memory Modules (DDR4 / DDR5).

Processor Internals

2. CPU Architecture & The Machine Cycle

The Central Processing Unit (CPU) is the computational engine of the computer. It operates through continuous execution of the 4-step Machine Instruction Cycle:

The 4-Step CPU Machine Instruction Cycle

Key CPU Internal Registers:

Program Counter (PC): Holds the memory address of the next instruction to be fetched.
Memory Address Register (MAR): Holds the physical memory address currently being accessed for read/write.
Memory Data Register (MDR) / MBR: Holds the actual data/instruction fetched from or waiting to be written to memory.
Instruction Register (IR): Stores the current instruction while it is being decoded by the Control Unit.
Accumulator (ACC): Stores the immediate intermediate results of arithmetic and logical computations from the ALU.

Peripherals

3. Input Devices (Comprehensive Guide)

Category	Device	Operating Mechanism & Applications
Typing & Text	Keyboard	Standard 104-key QWERTY layout. Uses matrix circuit switches to convert keystrokes into ASCII/UNICODE scan codes.
Pointing	Optical Mouse, Touchpad, Trackball	LED/laser sensor tracking optical surface displacement to position the on-screen graphical cursor.
Optical Recognition	OMR (Optical Mark Reader)	Detects the presence/absence of pencil or pen graphite marks by measuring reflected light on exam answer sheets.
Character Recognition	OCR (Optical Character Recognition)	Digitizes printed or handwritten physical paper documents into editable digital text files.
Banking Cheques	MICR (Magnetic Ink Character Recognition)	Reads characters printed in magnetic iron-oxide ink (E-13B font) at the bottom of bank cheques for rapid clearing.
Code Scanning	Barcode & QR Code Scanners	Photoelectric sensors reading 1D horizontal bars or 2D matrix blocks (Quick Response codes) for logistics and retail POS.
Biometrics	Fingerprint & Iris Scanners	Capacitive/optical mapping of unique biological ridges and retinal blood vessels for high-security identity verification.

Peripherals

4. Output Devices (Monitors & Printers)

Visual Output: Display Technologies

CRT (Cathode Ray Tube): Bulky legacy monitors using electron guns hitting a phosphorescent screen.
LCD (Liquid Crystal Display): Flat panels modulating polarized liquid crystals backlit by fluorescent tubes (CCFL).
LED (Light Emitting Diode): Modern LCDs using energy-efficient LED edge-lit or direct backlighting (IPS, VA, TN).
OLED (Organic LED): Each individual pixel emits its own light, delivering infinite contrast ratio and true blacks.

Printers: Impact vs. Non-Impact Comparison

Feature	Impact Printers	Non-Impact Printers
Printing Mechanism	Physical mechanical pins/hammers strike against an inked ribbon onto paper.	No physical contact with paper; uses laser electrostatics, thermal heat, or ink spraying.
Speed & Noise	Slow (measured in CPS - Characters Per Second); highly noisy.	Fast (measured in PPM - Pages Per Minute); near silent operation.
Print Quality	Low resolution; limited graphics capability.	Extremely sharp (measured in DPI - Dots Per Inch; up to 4800 DPI).
Carbon Copies	Yes (Can produce multi-part carbon copies due to physical impact).	No (Cannot make carbon copies).
Examples	Dot Matrix Printer (DMP), Daisy Wheel, Line Printer.	Laser Printer, Inkjet Printer, Thermal Printer.

Storage Architecture

5. The Computer Memory Hierarchy

Computer memory is engineered as a multi-tier hierarchy to balance the tradeoff between Access Speed, Cost per Byte, and Storage Capacity:

5-Level Memory Hierarchy Pyramid

Primary Memory: RAM vs. ROM

Parameter	RAM (Random Access Memory)	ROM (Read-Only Memory)
Volatility	Volatile (Data is lost immediately when power is turned off).	Non-Volatile (Data is retained permanently even when powered off).
Read/Write	Both Read and Write operations permitted at runtime.	Primarily Read-Only during regular computer operations.
Contents Stored	Active operating system files, open apps, and runtime data.	Firmware, BIOS/UEFI, and Bootstrap loader routines.
Sub-Types	SRAM (Static RAM), DRAM (Dynamic RAM, DDR4, DDR5).	PROM, EPROM (UV-erasable), EEPROM (Electrically erasable / Flash).

Quick Exam Revision Points

CPU Register for next instruction: Program Counter (PC).
Fastest memory inside a computer: CPU Registers, followed closely by L1 Cache.
Printer speed metrics: CPS (Characters Per Second), PPM (Pages Per Minute).
Printer resolution metric: DPI (Dots Per Inch).
MICR character font: E-13B magnetic ink font.