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Difference between main memory, backing storage & backup copies
It is very easy to be confused by the difference between memory (sometimes called internal storage or main
memory) and secondary storage (sometimes called backing storage).
Secondary storage (backing storage) is the permanent storage where programs and files are stored. Another name
for permanent is non-volatile. It is called permanent storage because its contents are not lost when the computer is
turned off. Hard disks, CDs, DVDs, USB memory sticks etc are examples of secondary storage.
Most main memory (sometimes called internal memory) is not permanent but is temporary - that means its contents
are lost when the computer is turned off. Another name for temporary is volatile. This memory is called RAM and this
is where the program you are currently working on is stored whilst you are working on it. We covered this way back
in year 10 - I probably opened a Word document on the whiteboard, typed in some text & then asked why everyone
could still see what I had typed even though I hadn't saved it. The reason we could see it was because the computer
temporarily stores what we are doing in the RAM. If we just turn off the computer everything is emptied out of the
RAM; in other words it is temporary. If we want to keep our work after the computer is turned off we have to move
it from the RAM to secondary storage - how do we do that? We save it onto the hard disk or a USB memory stick etc.
As well as RAM there is a small amount of main memory called ROM which is permanent memory. ROM stores all the
instructions needed to enable the computer to start up when you turn the power on. When you first turn the power
on your computer you have to wait a few minutes before you can use it. Why? Because the computer has lots of
parts inside that need to be turned on, connected, checked etc. The ROM stores all the instructions to make sure
these jobs are done so that the computer gets turned on ready for us to use. This is called booting up the computer.
You can't save anything to the ROM - all the information in it has been put there when the computer was made.
Do not confuse backup copies with backing storage. Backing storage is another name for secondary storage.
Backing storage is the name for any device we use to permanently save files and software e.g. hard disk, CD-RW,
CD-R, USB memory stick, magnetic tape etc. Backup copies are when you save a 2nd copy of a file somewhere
different from where you originally saved it just in case something happens to the original. E.g. you might save a
piece of coursework on the hard disk of your computer (a backing storage device) and then save a backup copy on a
USB memory stick (also a backing storage device).
Name Also called: What is it?
RAM Main memory (it's the biggest part of Volatile memory - it loses everything in it
main memory) when the computer is turned off
Internal storage Temporarily stores the work you are doing on
Memory the computer whilst you are doing it
ROM Main memory (it's the smallest part of
Non-volatile memory - it permanently stores
the main memory) data
It remembers what is in it when the computer
is turned off so it is still there when you next
turn it on
Stores the instructions so that the computer
can turn on (boot up)
Backing storage Secondary storage Non-volatile storage - permanent storage so
There are lots of backing storage what is in it is still there when the computer is
devices e.g. hard disk, CD-RW, CD-R, next turned on
USB memory stick, magnetic tape etc Where you save the programs on your
computer e.g. Microsoft Word
Where you save files that you want to keep