The amount of storage on a hard disk, measured in gigabytes and terabytes. Hard drive capacity is generally measured by the amount of data users need to store, which is usually much greater than the space applications take up. For example, photos and especially video are considerably larger than text documents. We've Come a Long Way! In 1957, the cost of one megabyte of storage on the first hard drive would cost the equivalent of USD $200,000 in today's dollars. However, in 2015, one megabyte of hard drive storage cost 1/300th of a cent! See hard disk, byte and space/time.