That Blue Square Thing

AQA Computer Science GCSE

This page is up to date for the AQA 8525 syllabus for exams from 2022.

4.7 Computer Systems – Secondary Storage

Secondary storage is any non-volatile memory which can't ba accessed directly by the CPU.

It includes the hard drive as well as removable media such as USB memory sticks, CDs, DVDs, floppy disks, tape backups and the like.

PDF iconSecondary Storage Intro – slides from class

Main Memory and Secondary Storage:
Main memory is the computer's working memory – the RAM.
Data is stored long-term in secondary storage. These are non-volatile storage media which can be changed, deleted and reused. They can even be removed from a computer and used in another one.
Data is copied from secondary storage into main memory when it's needed. It's then worked on and a new version can (but doesn't have to be) saved back on to the secondary storage so that it can be stored long-term.

Three types of secondary storage

There are three categories of secondary storage: magnetic, optical and solid state. Each stores data differently.

PDF iconSecondary Storage Table – slides from class

PDF iconSecondary Storage – detailed notes

Based on points from markschemes, I've produced a revision summary for each of the three types of secondary storage. This stuff comes up very regularly, so it's well worth taking the time to take a read through these:

PDF iconMagnetic storage – exam prep

PDF iconOptical storage – exam prep

PDF iconSolid state storage – exam prep

The bullet points on those slides are taken from markschemes for optical and magnetic storage. As of 2021, the exam board has never asked the "explain how it operates" question for solid state storage, so I've come up with a list of points I think would be included for that.

You might find this YouTube videowiki link helpful as a summary if you prefer to listen to things. It doesn't quite have the detail about how each type works for top-end marks, but it's a decent job.

Solid state storage

There's a lot more detail on solid state storage below. The reasons for this are:
a) it's a bit more complex than the other types
b) it's not come up on a live exam paper yet
c) the exam board seem to like asking 4 mark questions asking you to explain how types of storage actually work. These require some detailed knowledge and they've asked about magnetic and optical storage already.

PDF iconSolid State Storage – detailed notes on slides

The other likely question might be to compare the pros and cons of different storage types. There is a summary of solid state pros and cons on the slides above and detail about the others in the notes above that.

Cloud Storage

Cloud storage involves saving data "in the cloud" and accessing it using the internet - usually using a web browser. This has a number of pros and cons associated with it.

PDF iconCloud Storage Intro – slides from class

The detail on cloud storage can be found in the Unit 8 - Cloud Storage page. This part of the syllabus crosses over totally between the two units.