Orpington Astronomical Society

Astronomy => Technical => Topic started by: Fay on Jul 04, 2008, 10:10:23

Title: camera card size
Post by: Fay on Jul 04, 2008, 10:10:23
How many MB's in a Gig?

Thanks
Title: Re: camera card size
Post by: RobertM on Jul 04, 2008, 10:19:32
1024Mb = 1Gb
Title: Re: camera card size
Post by: Fay on Jul 04, 2008, 10:25:50
Thanks Robert
Title: Re: camera card size
Post by: Ian on Jul 04, 2008, 10:27:51
Depends. There should be 1024M in 1G whether that's bits or bytes.

However, hard drive manufacturers have long since ignored that convention and stuck to 1000. Looking at a 1GB card I've got, it looks like solids state memory is the same. It's capacity is 986M, not 1024M which it really should be.
Title: Re: camera card size
Post by: Mike on Jul 04, 2008, 10:42:05
Quote from: Ian on Jul 04, 2008, 10:27:51...hard drive manufacturers have long since ignored that convention and stuck to 1000.

Which is very irritating. The only reason they do it is to be able to sell HD's at such and such a capacity when in fact it is 2.34% less than advertised !!
Title: Re: camera card size
Post by: RobertM on Jul 04, 2008, 10:55:29
986Mb would be the available size after formatting but yes Ian is right about the hard drive con trick ... 250GB hard drive = 250 real GB - wrong, what they are referring to is 250,059,350,016 bytes (or thereabouts) which is in fact 232 real GB.

Memory sticks, usb drives etc based on silicon memory should have the correct number of bytes.  What you see after formatting should be just over 90% of the quoted capacity once the OS has robbed you for the file system.

FWIW I bought two 4Gb SD cards recently for my 450d but cost was the overiding factor rather than speed - that may be different if you want to capture a quick sequence.
Title: Re: camera card size
Post by: Rick on Jul 04, 2008, 10:58:56
Technically, the disk drive manufacturers are at least partly correct. The relevant S.I. prefixes are K=1000, M=10^6, G=10^9, T=10^12. The computer folk came late to the game and used the prefixes sloppily. If you want to be clear, there are prefixes for the relevant power-of-2 steps. They are Ki=1024, Mi=1024*1024, Gi=1024*1024*1024 etc.

The other catch is that, strictly speaking, "b" means bits while "B" refers to bytes (usually, but not always 8 bits long). The broadband folk love this, because they can claim that a line is (say) 8Mb/s (meaning 8000000 bits per second).
Title: Re: camera card size
Post by: mickw on Jul 04, 2008, 18:00:07
I usually get memory here -

http://www.shop4memory.com/


Good prices, good service from Ireland hence Euros.

Could actually have done with some memory on Tuesday  :(