Computer Studies / Data Processing · Lesson 2

Input/output devices, CPU, memory, storage units, registers and buses

JAMBWAECNECO

What the syllabus asks

JAMB: Section B 1(c) Computer hardware: CPU (ALU, CU, registers), peripherals (input and output devices) and storage media; keyboard key classification; mouse; scanner, light pen, joystick, digital camera, voice; monitor, printer (inkjet, laser, line), speaker, plotter; primary memory (RAM, ROM) and secondary storage (floppy, tape, hard disk, CD, DVD, USB); comparative analysis of auxiliary storage;…

WAEC: Computer hardware (input devices, output devices, CPU, memory unit, units of storage and interconversion); Computer data conversion (registers MDR, CIR, SCR; register vs main memory; bus speed and width; fetch–execute cycle not required)

NECO: Computer hardware (input devices, output devices, CPU, memory unit, units of storage and interconversion); Computer data conversion (registers MDR, CIR, SCR; register vs main memory; bus speed and width; fetch–execute cycle not required)

What you will learn

Define hardware and draw a block diagram of a computer.
Describe input devices and classify keyboard keys.
Explain the features and operations of the mouse.
Describe output devices and compare inkjet, laser and line printers.
State the components and functions of the CPU.
Distinguish RAM from ROM and primary from secondary storage.
Compare secondary storage devices by capacity, speed, cost and access method.
Convert between units of storage.
Define registers, bus and address and explain the functions of named registers.
Explain how bus speed and bus width affect data transfer.

Key points

Hardware: physical parts. Units: input, CPU (CU, ALU, registers), memory, output; peripherals attach externally.
Input devices: keyboard, mouse, scanner, joystick, light pen, microphone, camera, touchscreen, barcode reader, MICR, OMR, biometrics.
Keyboard keys: function, alphanumeric, numeric keypad, cursor, and special/modifier keys.
Mouse operations: point, click, double-click, right-click, drag and drop, scroll.
Output: monitor (CRT, LCD/LED, OLED), printer, plotter, speaker, projector; soft vs hard copy.
Impact printers: dot-matrix, line. Non-impact: inkjet (liquid ink), laser (toner, fastest page printer), thermal.
CU fetches, decodes and directs; ALU does arithmetic and logic; registers hold current items.
RAM: read/write, volatile. ROM: read-only, non-volatile, holds BIOS/firmware.
Secondary storage: HDD, SSD, flash, CD/DVD/Blu-ray, tape (sequential), cloud.
1 nibble = 4 bits; 1 byte = 8 bits; KB→MB→GB→TB each × 1,024.
Smaller unit: multiply; larger unit: divide.
PC/SCR: next instruction address; MAR: address; MDR/MBR: data; CIR: current instruction; AC: results.
Address bus (one-way), data bus (two-way), control bus (signals); n address lines → 2^n locations.
Transfer speed rises with bus width and bus speed.
Registers are faster and far smaller than main memory.

Start here: Hardware and the block diagram of a computer

Hardware is every physical part of a computer system: the parts you can see and touch. The system unit (the case of a desktop, or the body of a laptop) holds the motherboard, CPU, memory, storage drives and power supply. Devices connected to it from outside, such as printers, scanners and external drives, are called peripherals.

The functional units

Input unit: devices that bring data and instructions in.
Central processing unit (CPU): the control unit, arithmetic and logic unit (ALU) and registers. It carries out instructions.
Memory unit: main (primary) memory holds the program and data being used; secondary storage keeps them permanently.
Output unit: devices that give results.

Data flows from input to the CPU and memory, is processed, and flows out to output or storage. The control unit coordinates all units. The WAEC Computer Studies syllabus notes that the CPU together with the memory unit is often called the system unit.

Motherboard

The motherboard (system board) is the main circuit board. The CPU, RAM and expansion cards plug into it, and the buses printed on it connect them. Ports on its edge connect peripherals (USB, HDMI, audio, network).

Worked example 2.1 (WAEC-style)

Draw and label a block diagram of a computer system and state the function of each unit. (8 marks)

Draw input → CPU (control unit, ALU) → output, with memory connected to the CPU and arrows showing data flow. Functions: input enters data; control unit directs and coordinates; ALU calculates and compares; memory stores program and data; output presents results.

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Practice questions

1. Which of these is an input device?

Scanner
Monitor
Printer
Speaker

Show answer

A: Scanner
Scanners capture images into the computer.

2. Which device reads the magnetic ink characters on cheques?

OMR
OCR
Plotter
MICR

Show answer

D: MICR
Magnetic ink character recognition.

3. The ALU performs

printing
booting only
arithmetic and logical operations
storage of files

Show answer

C: arithmetic and logical operations
The control unit directs; the ALU calculates and compares.

4. RAM is described as volatile because

it is permanent
its contents are lost when power is switched off
it cannot be written to
it is slow

Show answer

B: its contents are lost when power is switched off
ROM is non-volatile.

5. Cache memory is used to

hold frequently used data close to the CPU for speed
store files permanently
print documents
connect to the internet

Show answer

A: hold frequently used data close to the CPU for speed
It is faster than main RAM.

Key words

Hardware: The physical parts of a computer system.
Peripheral: A device connected to the system unit, such as a printer or mouse.
Input device: A device used to enter data and instructions into a computer.
Output device: A device that presents processed results to the user.
Soft copy: Output displayed on a screen or stored electronically, not printed.
Hard copy: Printed output on paper or film.
CPU: Central processing unit: control unit, ALU and registers; the “brain” of the computer.
Control unit: The part of the CPU that fetches, decodes and directs the execution of instructions.
ALU: Arithmetic and logic unit: performs calculations and comparisons.
Register: A very small, very fast storage location inside the CPU.
RAM: Random access memory: volatile read/write main memory.
ROM: Read-only memory: non-volatile memory holding permanent instructions.

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