The piece of hardware that stores your programs and data "permanently" - ie after the power goes off. You probably know what a hard disk is.
Hard drives used to have capacity measured in Megabytes (MB) - these days it is more likely to be in Gigabytes (GB) or maybe (very unlikely) Terabytes (TB).
The standard method of measuring large amounts of data (in the mainstream media) appears to be Library of Congress x n.
45 pages link to HardDisk: