For memory & hard drive size, it probably doesn't-but it's a poor habit to develop because in other areas (communications, especially) it does. (Also note that hard drive size is measured in two ways-both using the MB/GB abbreviation but coming up with different values for the same 'size'. If it seems like that difference is important then you probably ought to express the size in actual bytes, e.g. 300,000,000,000B rather than 300GB (which, if using what I consider the correct definition of gigabyte, is 322,122,547,200B.)