Computer storage

[alanogden]

Why are CF and SD cards always in multiples of 4 Mb - could they be 3, 6 or 27 Mb?

[ugly_bob]

It's a standard.
All memory is like that.
1MB, 2MB, 4MB, 1GB, 2GB, 4GB etc.
always in powers of 2 of 1 byte.
(btw 1KB = 1024 bytes, not 1000 bytes, 1MB=1024KB etc)

[alanogden]

I realise that but why has it become a standard? Why did we get 8 bits in a byte? I understand that some calculators have 5 bits in a byte and IBM used to have 9 bits with the last one for parity

[mattfox]

This could be a help

http://en.wikipedia.org/wiki/Byte

or this

http://computer.howstuffworks.com/bytes.htm

[fo3nix]

We could in decimal, i.e. from 0 to 9, then 10, 11, 12, etc.

Computers use binary, which is just another number system, but it's not as obvious to us humans (we probably use decimal because we have 10 digits on our hands).

Binary means either 0 or 1, and combinations of lots of them. So there's a total of 2 numbers to choose from (hence the 'bi' part of binary). And so all numbers that computers use are multiples of 2:

2^1 = 2
2^2 = 4
2^3 = 8
2^4 = 16
2^5 = 32
2^6 = 64

etc.

[fo3nix]

sorry, 'could' in the first line of my answer should be 'count'!

[alanogden]

Thanks to all - that has been most helpful especially the web-sites. Alan