A hard drive, or hard disk drive (HDD), is the storage device you use in your personal computer (PC). These are non-volatile storage devices used to store the data of your computermeaning you can be assured that whatever data is stored in these devices, it cannot easily be erased. However, there is no guarantee that your HDD would not encounter problems causing it to crash and causing you to eventually loose your data.

Inside the HDD, there are many mechanisms that move around to perform read and write functions. The HDD is made of rotating platters, commonly called disks. Each of these platters has a planar magnetic surface where the data is stored. This data is sent to a read-write head, which sends an electrical charge, executing the transaction. These moving parts and electrical charges could possibly cause the breakdown of your HDD, but manufacturers have already designed firmware into the HDD to allow more efficient scheduling of reads and writes if the HDD surface and the remapping of sectors of the disk fail. Also, HDD manufacturers have collaborated with motherboard makers in developing the Self-Monitoring, Analysis, and Reporting Technology, or S.M.A.R.T., that can warn you of possible failures, allowing you to make necessary backups before data loss occurs.

An HDD is accessed with the following bus types: ATA (which includes IDE and EIDE), SATA, SCSI, SAS, FireWire (or IEEE 1394), USB and Fibre Channel. Aside from the connection, you have to select your HDD by the capacity, nowadays measured by gigabytes; the physical size, normally, if you are using a desktop, you would need a 3.5 HDD, whereas 2.5 is what you would use for a laptop; the reliability or the estimated number of uses before you HDD fails; speed or the number of reads and writes per second; power consumption; transfer rate; random access time; and the G-shock rating, which is very important if you plan to travel with your HDD a lot.