ICT 0417 – Storage Devices and Media: Magnetic Drives
Storage Devices and Media – Magnetic Drives
Magnetic storage uses the magnetic properties of iron‑oxide coated surfaces to record and retrieve digital data. In the IGCSE ICT syllabus the focus is on three main types of magnetic drives:
Fixed (internal) magnetic hard drives
Portable (external) magnetic hard drives
Magnetic tape drives
1. Fixed Magnetic Hard Drives (Desktop HDD)
A fixed magnetic hard drive is a non‑volatile storage device permanently installed inside a computer chassis. Data is stored on rotating magnetic platters.
Key components
Platters – coated with a thin magnetic layer
Spindle motor – rotates the platters at a constant speed (e.g., 5400 rpm, 7200 rpm)
Read/Write heads – positioned on an actuator arm to access tracks
Actuator arm – moves the heads radially across the platters
Controller board – manages data transfer to/from the computer
Advantages
High storage capacity (up to several terabytes)
Fast random‑access performance
Relatively low cost per gigabyte
Disadvantages
Mechanical parts are vulnerable to shock and wear
Consumes more power than solid‑state alternatives
Noise from spinning platters and actuator movement
Parameter
Typical \cdot alue (Desktop HDD)
Capacity
500 GB – 8 TB
Rotational Speed
5400 rpm or 7200 rpm
Interface
SATA III (6 Gb/s) or older IDE
Average Seek Time
5 ms – 12 ms
Power Consumption (Idle/Active)
≈ 5 W / 8 W
2. Portable Magnetic Hard Drives (External HDD)
Portable magnetic hard drives are essentially fixed HDDs enclosed in a protective case with an external interface, allowing them to be connected to any compatible computer.
Typical interfaces
USB 2.0 (480 Mbps)
USB 3.0/3.1 (5 Gbps – 10 Gbps)
eSATA (6 Gbps)
Thunderbolt (up to 40 Gbps)
Power source
Bus‑powered via USB (most common)
External AC adapter for high‑capacity models
Advantages
Easy to transport – useful for backups and data transfer
Plug‑and‑play with most operating systems
Large capacities comparable to internal drives
Disadvantages
Still contains moving parts – susceptible to drops
Generally slower than SSD‑based portable drives
Requires a physical connection (no built‑in wireless)
Parameter
Typical \cdot alue (External HDD)
Capacity
1 TB – 5 TB
Interface Speed
USB 3.0 (5 Gbps) – 10 Gbps
Dimensions
2.5 in (portable) or 3.5 in (desktop‑style)
Power
Bus‑powered (2.5 in) or AC adapter (3.5 in)
Typical Transfer Rate
80 MB/s – 150 MB/s
3. Magnetic Tape Drives
Magnetic tape drives store data on a long, thin strip of magnetic material wound onto a reel or cartridge. Data is written and read sequentially as the tape moves past a stationary read/write head.
Common formats
Cassette (e.g., DAT)
Cartridge (e.g., LTO – Linear Tape‑Open)
Reel‑to‑reel (used in large‑scale archival systems)
How it works
The tape is pulled from the supply reel, passes over the head, and is wound onto a take‑up reel.
Data is recorded in linear tracks; modern LTO uses multiple parallel tracks per pass.
Advantages
Very high capacity per cartridge (up to 30 TB compressed for LTO‑9)
Low cost per gigabyte – ideal for long‑term archival
Durable when stored properly; resistant to electromagnetic interference
Disadvantages
Sequential access – slower for random‑read/write operations
Requires a dedicated tape drive and management software
Physical wear of the tape and head over many passes