kilobit, kilobyte, megabit, megabyte, gigabit,

gigabyte

With all of these, there's the technical meaning, the common meaning, and the possible meaning. Sometimes these all merge, sometimes they don't.

First, forget the metric system. A kilometer and a kilobyte only look like they are based on the same standard. A kilometer is 1,000 meters, but a kilobyte is 1,024 bytes. A megabyte is either 1,024 * 1,024 bytes (if you are measuring ram) or 1,000,000 bytes (if you are measuring a disk drive). There's another difference with those two also: quantities of ram will almost always be expressed as powers of two, and sizes of disk drives almost never will be except by accident. So while mentioning your 128 GB disk drive won't make you look like a dweeb, saying you have 100 MB of ram surely will. Finally, having a GB of ram means you really do have 1024 * 1024 * 1024 bytes, but having a 40 GB drive means you have something slightly less than 40,000,000,000 bytes because of formatting losses and locked out defects.

The case of suffixes makes a difference: Mb is megabits, MB is megabytes. And although there are 8 bits in a byte, you'd usually need to divide kbits or mbits by 10 to get kbytes or mbytes if you are trying to figure out how long it's going to take to transmit so many gigabytes of data over that 56kb (which is really less than that, of course) link. If you want to get really techy, you'll need to figure in packet payloads at a minimum, but the the 10 bit figure is close enough for deciding whether or not you can go to lunch, though not necessarily useful for determining which day next month this transfer might be done.

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