Secondary Storage

AQA 4.6.3 — Secondary storage

Retrieval: the previous lesson established that RAM is volatile and far too small and expensive to hold everything permanently. This lesson covers where data actually lives long-term instead — and you'll recognise the file-size numbers involved from Sequence 7's storage calculations directly.

Key vocabulary

• Secondary storage — non-volatile storage that holds data and programs even with the power off.
• Magnetic storage (HDD) — stores data on spinning magnetic platters, read/written by a moving head.
• Solid-state storage (SSD) — stores data electronically in flash memory cells, with no moving parts.
• Optical storage — stores data as physically etched patterns read by a laser (CD/DVD/Blu-ray).

Understand — why secondary storage exists at all

RAM is fast but volatile and comparatively small; secondary storage is slower but non-volatile and can hold vastly more, far more cheaply per gigabyte. A computer needs both: RAM for what's actively being worked on right now, and secondary storage for everything that must still exist the next time the computer is switched on.

Explain — the mechanism behind HDD vs SSD

A hard disk drive (HDD) stores data magnetically on spinning platters; a physical read/write head has to move to the correct position on the disk before it can access data — this physical movement is the main reason HDDs are comparatively slow, especially for accessing many small, scattered files. A solid-state drive (SSD) instead stores data electronically in flash memory cells with no moving parts at all, so any piece of data can be reached in roughly the same, very short time regardless of where it's physically stored on the chip — which is exactly why SSDs are dramatically faster, especially for random access.

Visualise — comparing the technologies

Common mistake

Assuming an SSD has no limit at all on how much it can be written to. Flash memory cells do wear out after a large number of write cycles — a real, if usually distant, limitation that doesn't apply to magnetic HDDs in the same way, even though SSDs are faster and more durable against physical shock.

Apply it — recommend and justify

For each scenario, recommend a storage technology and justify your choice using at least two criteria from the table above:

1. A field photographer needs to transport 500 GB of RAW photo files to a client and the storage must survive being dropped in a bag.
2. A school wants the cheapest possible long-term archive of ten years of lesson recordings, rarely accessed again.
3. A video editor needs to scrub back and forth through large video files as fast as possible while working.

(1: SSD — no moving parts to damage from a drop, and fast enough to transfer large files quickly. 2: HDD or cloud — lowest cost per GB for large, rarely-accessed archives; speed barely matters here. 3: SSD — fast random access is exactly what scrubbing through video repeatedly needs.)

Challenge

A school's IT department is deciding between HDDs and cloud storage for backing up every student's coursework. Identify one genuine advantage of each option that the other cannot fully replace, and recommend which matters more for a school specifically.

Looking ahead: the next lesson (System Software) moves from the physical hardware that stores and processes data to the software that manages and coordinates all of it — the operating system.