The amount of storage on a hard disk, measured in gigabytes and terabytes. Hard drive capacity is measured by the amount of data users need to store, which is often much greater than the space applications take up. For example, a single video can take four gigabytes of space.We've Come a Long Way!In 1957, the cost of one megabyte of storage on the first hard drive would be the equivalent of USD $200,000 in today's dollars. However, in 2017, one megabyte of hard drive storage costs less than 1/3000th of one cent! See hard disk, byte, SSD and space/time.