Hard disk drive (HDD)
The hard disk, also called HDD (Hard Disc Drive), is the device that stores your data on your machine, your documents, your games, your operating system (Windows, Mac, ...), ...
Without it you could not use your computer. Its size varies according to need, hard disks today exceed hundred Gigabytes.
There are several kinds of hard drive. Currently the most widespread is the SATA. Ancienement we used the IDE.