What is the difference between GiB and GB?

The difference between 1 KiB and 1 KB is 1024−1000 bytes. The difference between 1 GiB and 1 GB is 10243−10003 bytes.

The "ibi" (or binary prefix) units (kibi, mebi, gibi) are based on 210 (1024), where the standard decimal units (kilo, mega, giga) are based on 103 (1000). Before the MiB was in use, MB often was ambiguous - was it binary or decimal? Often storage manufacturers would advertise using decimal, since 100GB is smaller than 100GiB (100GB is actually 93GiB and some change), while internally operating systems worked in binary units (the disk size and file size was always reported in GiB). Memory (RAM) manufacturers have always been using MiB/GiB, even though labeled "MB/GB".

Traditionally, the kilobyte was 1024 bytes, the megabyte was 1024 kilobytes, etc… This especially makes sense for RAM (since they have to be built in multiplies of 1024 anyways)

But some people also used 1000 bytes in a kilobyte, 1000 kilobytes in a megabyte and so forth… mostly hard disk and bandwidth vendors as it allows for a small gain in displayed amounts. This resulted in some lawsuits, so standards bodies came up with the solution of renaming “1024” kilobytes as “kibibytes”, megabytes as “mebibytes” and so forth.

I don’t think I’ve actually heard anyone ever PRONOUNCE these words though. In practice people say “k/meg/gig” etc, and you just have to guess if it’s a 1024 or 1000 version by context. 

So now you know