Storage devices, media and backups
The three storage types, how they compare, and why backups matter.
Review these first
Learning objectives
What you need to be able to do
Teacher-mapped phrasing — check against the official Cambridge syllabus for exact wording.
- 3.1.1Describe magnetic, optical and solid-state storage and compare their characteristics.
- 3.1.2Explain the purpose of backups and appropriate backup media.
5 minute read
Storage devices, media and backups
The three technologies
Magnetic — hard disk drives (HDD), magnetic tape. Data is stored as magnetised patterns on a spinning platter or tape. Very large capacity and low cost per gigabyte, but contains moving parts, so it is slower and vulnerable to physical shock. Optical — CD, DVD, Blu-ray. Data is read by a laser detecting pits and lands. Cheap and portable, but comparatively small capacity and easily scratched. Solid state — SSD, USB flash drive, memory card. Data is stored electronically in flash memory with no moving parts, so it is fast, silent, robust and power-efficient. The trade-off is a higher cost per gigabyte and a finite number of write cycles.
Choosing between them
Match the property to the need: an SSD in a laptop for speed and durability; a large HDD or tape for cheap bulk storage and archiving; optical discs for distributing software or films cheaply.
Backups
A backup is a second copy of data kept so it can be restored if the original is lost through hardware failure, accidental deletion, theft, fire or a malware attack. Good practice: keep backups off-site or in the cloud so one fire or burglary cannot destroy both copies, back up regularly and automatically, and occasionally test that a restore actually works. Note the distinction from an archive: a backup duplicates data still in use, whereas an archive moves data that is no longer needed day to day into long-term storage.
Think of it like this
A backup kept next to the computer is like a spare key kept in the same pocket as the original. It solves the problem of losing one key, but not the problem of losing the pocket.
Worked examples
Method, step by step
A company stores customer records on a server in its office. Explain why it should keep a backup off-site.
- 1A backup protects against data loss from hardware failure, deletion or malware.
- 2If the backup is kept in the same building, a fire, flood or theft would destroy both the original and the backup.
- 3Keeping it off-site or in the cloud means the data survives an event affecting the office.
Because a fire, flood or theft at the office would destroy the original and an on-site backup together. An off-site or cloud backup survives such an event, so the records can still be restored.
Common misconceptions
- Thinking a backup on the same hard disk counts. If the disk fails, both copies go — a backup must be on separate media.
- Believing SSDs are simply "better". They are faster and more robust, but cost more per gigabyte, which is why bulk archives still use magnetic media.
- Confusing backup with archive. Backups are copies of live data; archives are long-term storage of data no longer in active use.
In the exam
- When comparing storage, use the standard criteria: capacity, speed, cost per gigabyte, portability and durability. Answering across those five reliably earns the marks.
- For backup questions, always include where the backup is kept — "off-site or in the cloud" is frequently a separate marking point.