Main Memory Vs Backing Storage

This is a common GCSE Computing question and a key area for any computer science student to understand.

There are essentially two types of data storage that a computer uses:

Main Memory or Primary Storage

This is where the computer hold any data it is working on at the moment. Music that is playing, images on screen, Word docs you have open, etc. RAM is the main type of main memory and is VOLATILE. This means it wipes itself whenever the power turns off.

Backing Storage

This is where data is stored long term, it is NON-VOLATILE so it does not wipe when the power goes off. You hard drive, CDs and USB sticks are all backing storage.

An analogy:

Imagine RAM as your hands and Backing Storage as your rucksack. You can hold loads of stuff in your rucksack and if you suddenly pass out it`ll be safe in there. But you can`t use it unless you get it out and use it with your hands. Your hands are fast, but space is limited and if you suddenly pass out (let`s say you do that) then you drop everything and lose it. If you have too much stuff in your hands you have to start swapping things in and out of your bag and swapping tasks takes ages. You see this sometimes when you have a lot of windows open and it takes a long time to swap between them.

Overall:

Main Memory:

- RAM - Wipes when power goes off - Fast, but expensive so not much space - Connected to the processor so needed to use data

Backing Storage:

- Hard drives, USB sticks, CDs, DVDs, Blu Ray - Keep data even with no power - Slower, but cheaper so lots of space - Not connected to the processor, things must be moved into Main Memory to be used