Magnetic Storage — Memory and Storage | IGCSE Computer Science

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 5% of your exam marks.

stable

Rare

Stable5%

RAM vs ROM and primary vs secondary storage comparisons appear regularly.

stores binary data as the magnetic polarity of tiny regions on a metal platter, which spins at high speed inside a sealed enclosure.

How a hard disk drive (HDD) works

The drive contains one or more circular metal platters coated with a magnetic material.
The platters spin at high speed (typically 5400 or 7200 RPM).
A movable read/write arm holds an electromagnetic head close to the platter surface, but never touching.
To write a 1 or 0, the head magnetises the region beneath it to one polarity or the other.
To read, the head detects the polarity of the region as the platter spins past.
Data is organised in concentric tracks, and each track is divided into sectors.

Advantages and disadvantages

Advantages	Disadvantages
Very large capacity (multi-terabyte)	Moving parts are fragile; easily damaged by drops
Low cost per gigabyte	Heavy and bulky compared to SSDs
Moderate read/write speed	Slower than SSDs
	Prone to mechanical failure over time
	Audible (spinning platter, head movement)

Magnetic disks remain popular for bulk storage (backups, archives, large media collections) where price per terabyte matters more than speed.

Exam tip

Give features of magnetic storage

What comes up: "Give two features of magnetic storage" or a matching question asking you to link a description to the correct storage type.

Write (two marks): (1) Data is stored on spinning platters divided into tracks and sectors, and a moving read/write arm positions the electromagnetic head over the correct location. (2) The magnetic field of each tiny region on the platter surface determines whether it represents a binary 1 or 0.

Watch out: the mark scheme does not credit describing an HDD simply as "magnetic" or "uses magnets" without the extra detail. You need to mention the platter, the read/write arm or electromagnet, and (for a "how data is stored" question) the magnetic polarity representing 1s and 0s. Do not confuse this with optical storage — magnetic storage uses a physical read/write arm, not a laser.