|The difference is often referred to binary vs decimal counting. 1024 is 2 raised to the 10th power so it's a binary thing. So:|
1024 bytes = 1 KB
1024 KB - 1 Megabyte
1024 MB = 1 Gigabyte
But we tend to think decimally; that is, 1000 bytes per KB, 1000 KB per MB, etc. I think the 1024 figure was chosen simply because it's the closest power ot 2 to 1000. Anyway, using the figures above:
1 GB (decimal) = 1024 x 1024 x 1024 bytes or
1 byte = 1 GB (decimal) /(1024 x 1024 x 1024)
multiply each side by a billion
1 GB (binary) = 1 GB (decimal) /(1.024 x 1.024 x 1.024) or
1 GB (binary) = 1 GB (decimal) x 0.93132
So when you look at the drive's size on the box it came in or on the manufacturer's site you get the decimal figure. Your computer wants to show the binary figure, although most OS's show both figures when you check the drive's properties.
Sometimes people will say the manufacturer is ripping you off by using the decimal figure. That's not true. All the bytes are there, the computer just counts them differently.
Also note that for an old drive measured in MB the conversion fiugre is 1/(1.024 x 1.024) or 0.95367. For a drive measured in TB (assuming the TB size is exact) the conversion would be 0.90949.