The macosxhints Forums - 18Gig Install?

As if it wasn't confusing enough...

"Certain units are always understood as decimal even in computing contexts. For example, hertz (Hz), which is used to measure clock rates of electronic components, and bit/s, used to measure bit rate. So a 1 GHz processor performs 1,000,000,000 clock ticks per second, a 128 kbit/s MP3 stream consumes 128,000 bits (16 kB, 15.625 KiB) per second, and a 1 Mbit/s Internet connection can transfer 1,000,000 bits (125 kB, approx 122 KiB) per second (assuming an 8-bit byte, and no overhead).

"Because of this, a very confusing hybrid system is sometimes used, in which a "megabyte" means a thousand 1024-byte "kilobytes". Thus, as of 2005, manufacturers universally use the designation "1.44 MB diskette" for a product which holds neither 1.44×220 bytes nor 1.44×106 bytes, but rather 1.44×1000×1024 bytes (approximately 1.406 MiB, or 1.475 MB). Some manufacturers of disk-like flash memory seem to have adopted the somewhat dubious practice of selling drives measured in power of two multiples of decimal megabytes!

"Modern-day PC users, of course, regard both RAM and disk as kinds of storage and expect their capacities to be measured in the same way. Operating systems usually report disk space using the binary version. To the purchaser of a "30 GB" hard drive, rather than reporting either "30 GB" or "28 GiB", [your system] reports "28 GB". This creates hard feelings that have even led to legal disputes, sometimes made worse by other technical issues such as failure to distinguish between unformatted and formatted capacities and to account for the overhead inherent in disk file systems.

"CD capacities are always given in binary units. A "700 MB" (or "80 minute") CD has a nominal capacity of about 700 MiB. But DVD capacities are given in decimal units. A "4.7 GB" DVD has a nominal capacity of about 4.38 GiB."