SSC Notes / Computer Awareness / Chapter 2
Chapter 2 of 13

Computer Hardware

The physical components of a computer — CPU, input/output devices, and the fetch-decode-execute cycle that powers every instruction.

📖 ~14 min read 💻 SSC Computer Awareness

Introduction

Hardware refers to all the physical, tangible components of a computer — the parts you can touch. This chapter covers the CPU (the computer's "brain"), plus the standard input and output devices.

The CPU — Central Processing Unit

ComponentFunction
ALU (Arithmetic Logic Unit)Performs all arithmetic (add, subtract) and logical (comparison) operations
CU (Control Unit)Directs and coordinates the operations of the entire computer, without performing calculations itself
RegistersSmall, extremely fast storage locations within the CPU for temporary data during processing
Cache MemoryVery fast memory between the CPU and RAM, storing frequently used data for quick access
📌 CPU = "Brain of the Computer": The CPU is often called the computer's brain because it executes instructions from programs, though the CU and ALU divide the labour — CU manages the flow, ALU does the actual computation.

Fetch-Decode-Execute Cycle

Flowchart — How the CPU Processes an Instruction
Fetch — CPU retrieves the instruction from memory (RAM)
↓
Decode — Control Unit interprets what the instruction means
↓
Execute — ALU/CU carries out the instruction
↓
Store — Result is written back to memory/register

This cycle repeats billions of times per second, measured by the CPU's clock speed (in GHz).

Input Devices

DeviceFunction
KeyboardText/character input
MousePointer control, selection
ScannerConverts physical documents/images into digital form
MicrophoneAudio input
WebcamVideo input
JoystickUsed mainly for gaming, directional control
Barcode ReaderReads barcoded product information (common in retail)
OMR (Optical Mark Reader)Reads marked responses on forms (e.g., exam answer sheets)
MICR (Magnetic Ink Character Recognition)Reads magnetic ink characters, used in bank cheque processing

Output Devices

DeviceFunction
MonitorVisual display of output
PrinterProduces physical (hard copy) output
SpeakerAudio output
ProjectorDisplays output on a larger surface
PlotterProduces high-quality vector graphics/large drawings (used in engineering, CAD)

Printer Types

TypeTechnology
Impact Printer (Dot Matrix)Physical pins strike an ink ribbon onto paper — noisy, used for multi-part forms
Inkjet PrinterSprays liquid ink onto paper — good quality, common for home use
Laser PrinterUses toner and a laser beam — fast, high-quality, common in offices
3D PrinterBuilds a physical 3-dimensional object layer by layer from a digital design

Input/Output (Both-Way) Devices

  • Touchscreen — accepts touch input and displays output simultaneously.
  • Modem — sends and receives data over telephone/network lines.
✅ UPSC/SSC Focus: ALU vs CU function distinction · Fetch-Decode-Execute cycle sequence · Input vs output device classification · MICR (banking) and OMR (exam forms) specific-use devices · Printer type comparison.

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