Secondary Storage Types: Magnetic, Optical, and Solid-State

This lesson covers the three main types of secondary storage — magnetic, optical, and solid-state — as required by OCR J277 Section 1.2.2. You need to understand how each type works, its advantages and disadvantages, and when each is appropriate.

---

Why Is Secondary Storage Needed?

RAM is volatile — it loses all data when the computer is turned off. Secondary storage provides non-volatile, permanent storage so that data, files, and programs are preserved when the computer is powered down.

---

Type 1: Magnetic Storage

How It Works

Magnetic storage uses magnetised particles on a spinning surface to store binary data. The read/write head moves across the spinning platters to read or write data.

Key Example: Hard Disk Drive (HDD)

Feature	Detail
Mechanism	Spinning metal platters with magnetic coating; read/write head on an arm
Capacity	Very large — typically 500 GB to 20 TB
Speed	Moderate — typically 100-200 MB/s
Cost	Low cost per gigabyte
Durability	Contains moving parts — vulnerable to damage if dropped or shaken

Other Magnetic Storage

• Magnetic tape — used for long-term backup and archiving. Very high capacity and low cost, but very slow (sequential access — must read through the tape in order to find data).

---

Type 2: Optical Storage

How It Works

Optical storage uses a laser to read and write data. Data is stored as a pattern of pits (indentations) and lands (flat areas) on the surface of a disc. The laser reflects differently off pits and lands, which the drive interprets as binary 0s and 1s.

Key Examples

Disc Type	Capacity	Writable?
CD-ROM	~700 MB	Read-only (pre-pressed)
CD-R	~700 MB	Write once, read many
CD-RW	~700 MB	Rewritable
DVD	~4.7 GB (single layer)	Various (ROM, R, RW)
Blu-ray	~25 GB (single layer)	Various (ROM, R, RE)

Characteristics of Optical Storage