I am very disappointed to see that out of 5 answers, 4 were incorrect, and the correct answer is not on the top.

As Ryan said, kilo(k), mega(M), giga(G) are always powers of 10. So they are multipliers of 1000.

kibi(Ki), mibi(Mi), gibi(Gi) are powers of 2. So they are multipliers of 1024.

Depending on what are you referring to, you may want one or the other.

Memory (as in RAM) is measured in powers of 2. So a RAM card could have 1GiB (one gibibytes or 1024 mibibytes) or 512MiB.

Storage doesn't need to be in powers of 2, so it can be human friendly power or 10. So a file could have 10GB (10 gigabyes, 10 000 megabytes)

Network speeds also don't need to be powers of 2. But they are usually measured in bites per second.

So Ethernet has a speed of 10 or 100 or 1000 megabites per second. A speed of 8megabits per second can also be called a speed of 1megabyte per second.

There is nothing wrong in saying a speed of 1Gibibits (meaning 1024 Mibibits, meaning 1024*1024*1024*1024 bits) but it would be needlessly confusing.

Hope this helps.

Source(s):
http://physics.nist.gov/cuu/Units/binary.html