Every computer – from a laptop to the computer inside a microwave – has the same main parts: input devices, a central processing unit (CPU), primary memory, secondary storage and output devices. In this post you will learn what each part does and how they work together in the IPOS cycle.

This builds on What Is Information Technology?, where we saw that IT is about collecting, processing and storing information.

Build on what you learned in Forms 1–3

These Lower School ICT posts cover the basics of this topic:

• The Functions of the Main Components of a Computer System – your first look at input, processing, storage and output
• What is hardware? – the physical parts of a computer system
• SD Card Reader – a common storage device and how it connects

In this post:

• The major hardware components and their functions
• Primary memory: RAM and ROM
• Secondary storage devices
• Units of storage (bits to terabytes)
• The IPOS cycle – how the parts interrelate

The major hardware components

Component	Function	Examples
Input	Gets data and instructions into the computer	Keyboard, mouse, scanner, microphone
Central Processing Unit (CPU)	Carries out (executes) instructions and processes data; controls the other parts	Intel Core i5, AMD Ryzen, phone processors
Primary memory	Holds the data and instructions the CPU is using right now	RAM, ROM
Secondary storage	Keeps data and programs permanently, even when the power is off	Hard disk, flash drive, memory card, DVD
Output	Presents the results of processing to the user	Monitor, printer, speakers

Video: IPO Cycle – https://www.youtube.com/watch?v=j0XOLp_PbgA

Primary memory: RAM and ROM

RAM (Random Access Memory)	ROM (Read Only Memory)
Volatile – contents are lost when the power is switched off	Non-volatile – contents stay when the power is off
Can be read from and written to	Can only be read (in normal use)
Holds the programs and data currently in use	Holds the start-up instructions (e.g. BIOS/firmware)
More RAM lets you run more programs at once	Usually small and fixed by the manufacturer

Image source: File:RAM Module (SDRAM-DDR4).jpg

Video: Primary Memory – https://www.youtube.com/watch?v=XY18amKzOvA

Secondary storage devices

• Hard disk drive (HDD): magnetic, large capacity, cheap per gigabyte, has moving parts.
• Solid state drive (SSD) / flash drive / memory card: flash memory, no moving parts, fast and portable.
• Magnetic tape: very large capacity, cheap; used mainly for backups and archives (serial access).
• Optical disks (CD, DVD, Blu-ray): read by a laser; used for distributing software, music and films.

Image source: File:Internal components of Hard disk drive.jpg

Video: Storage Devices – https://www.youtube.com/watch?v=OsEDJM9NuGA

For more on choosing where to keep your files, see Local Storage and Cloud Storage and Secondary Storage.

Units of storage

Computers store everything as bits (binary digits: 0 or 1).

Unit	Size	Roughly enough for…
Bit	0 or 1	one yes/no answer
Byte	8 bits	one character, e.g. “A”
Kilobyte (KB)	1 024 bytes	a short paragraph of text
Megabyte (MB)	1 024 KB	a phone photo (about 2–5 MB)
Gigabyte (GB)	1 024 MB	about 1 hour of HD video
Terabyte (TB)	1 024 GB	a whole computer’s hard disk

The IPOS cycle: how the parts work together

Input → Processing → Output, with Storage used throughout.

Example – calculating your term average:

• Input: the teacher types your marks using the keyboard.
• Processing: the CPU adds the marks and divides by the number of subjects, using data held in RAM.
• Output: the average appears on the monitor and is printed on your report.
• Storage: the file is saved on the hard disk so it can be opened next term.

Related

Related: recorded class on IPOS and primary and secondary memory (Form 4)

Paper 1 practice (multiple choice)

Choose the best answer for each question. Try them all before you check.

1. Which component carries out program instructions?
(A) Monitor
(B) CPU
(C) Hard disk
(D) Keyboard

2. Which type of memory loses its contents when the power is switched off?
(A) ROM
(B) RAM
(C) Hard disk
(D) DVD

3. How many bytes are in one kilobyte?
(A) 100
(B) 1 000
(C) 1 024
(D) 8

4. Which storage medium is MOST suitable for long-term backup of very large amounts of data?
(A) Magnetic tape
(B) RAM
(C) ROM
(D) CD

5. In the IPOS cycle, printing a report is an example of
(A) input
(B) processing
(C) output
(D) storage

Show answers

1. B
2. B
3. C
4. A
5. C

Paper 2 practice (structured question)

Keisha uses her laptop to type and save her class project report.

(a) State the function of the CPU. (1 mark)

(b) Give TWO differences between RAM and ROM. (2 marks)

(c) Name ONE suitable secondary storage device Keisha could use to carry her report to school, and give ONE reason for your choice. (2 marks)

(d) Using Keisha’s report as the example, explain the IPOS cycle. (4 marks)

(e) A photo is 3 MB. How many such photos can be stored on a 1 GB flash drive? Show your working. (2 marks)

Total: 11 marks

Show answers

(a) It processes data/executes instructions (and controls the other components) (1).

(b) Any two (1 each):
• RAM is volatile, ROM is non-volatile
• RAM can be read and written, ROM is read-only
• RAM holds programs/data currently in use, ROM holds start-up instructions

(c) Flash drive (1) – small/portable, plugs into any USB port (1). (Accept memory card or cloud storage with a valid reason.)

(d)
• Input – typing the report with the keyboard (1)
• processing – the CPU formats text/spell-checks (1)
• output – the report is shown on screen/printed (1)
• storage – the report is saved on the hard disk/flash drive (1)

(e) 1 GB = 1 024 MB (1); 1 024 ÷ 3 = 341 photos (1).

Next: Cloud Storage vs Local Storage: Capacity, Cost, Access and Security

Syllabus link: This post is relevant to the CSEC® Information Technology Syllabus (CXC 30/G/SYLL 17), Section 1: Computer Fundamentals and Information Processing, Specific Objective 3 (“explain the functions of the major hardware components of a computer system”); Specific Objective 4 (“explain how the major hardware components of a computer system interrelate”).

Attributions to media used in this post:

• RAM Module (SDRAM-DDR4).jpg – ElooKoN – CC BY-SA 4.0 (via Wikimedia Commons)
• Internal components of Hard disk drive.jpg – Imicrokallol – CC BY-SA 4.0 (via Wikimedia Commons)

© 2026 Vedesh Kungebeharry. All rights reserved.