That Blue Square Thing

AQA Computer Science GCSE

July 2019: the AQA CompSci area is almost complete. Most of the content for units 3-6 is now up and there's quite a lot of Unit 7 material. There's still some work to do, particularly on Paper 1 units, but it's getting there.

Computer Systems - Memory & Storage

The CPU uses main memory to store data and instructions.

Main memory is memory which is accessible directly by the CPU but which isn't a register or cache. It includes RAM and ROM (but is mainly RAM), but not a hard drive (which isn't directly accessible).

The differences between RAM and ROM are important to know here.

PDF iconMain Memory Intro - slides from class

PDF iconMain Memory - double page spread with detail

Main memory, and especially RAM, is the crucial element which has allowed the development of general purpose computers. It is flexible and can be used to hold either data or instructions as required. This is the memory part of the von Neumann architecture and is a major part of what makes modern computer systems able to do the jobs they need to do.

RAM in particular is important. More RAM is often considered useful and is a factor which can effect the performance of a computer.

PDF iconMore RAM - slides from class

BBC Bitesize has a useful set of pages about main memory and secondary storage that you might want to look at.

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

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

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 7 - Cloud Storage page. This part of the syllabus crosses over totally between the two units.