The hard drive has evolved considerably during the computer age, particularly with regards to capacity. While early computers had hard drives consisting of a paltry 5 to 10 megabytes of storage. Later data capacities are measured in gigabytes (1000 megabytes) and terabytes (1000 gigabytes). Typical consumers will have hard drives ranging from 150-500 gigabytes of data storage. For users who need to supplement their desktop or laptop's built-in hard drive, external hard drives are available. These drives are identical to their internal counterparts, but are encased in a plastic disk enclosure and can be used to connect to any computer to add storage space or to make backup copies of existing data.

2008's typical external hard drives average around 500 gigabytes of storage and utilize the common universal serial bus (USB) connection for data transfer. While flash drives are more compact and thus more convenient for transferring small amounts of data; external USB hard drives are ideal for handling large storage demands such as high-quality photos, videos, and music.