this is a very common question. basically, hard drive manufacturers use 1 billion bytes to mean 1 gigabyte, when there are really 1073741824 bytes in a gigabyte (one is base 10, the actual number is base 2). there is roughly a 7% discrepancy between actual size and advertised size so if you multiply the advertised size by .93 you will get approximately the size that will be available for use (i.e. 120 x .93 = 111.6)