A hard disk is a device for storing large amounts of data. Each disk comprises four basic elements that contribute to the disk parameters: media (platters), read/write heads, positioning device that positions the head to the needed track, and controller that ensures data transfer.
Hard disk performance depends on various parameters. The most important are write density, data-access time, amount of cache memory, and interface.
Increasing the write density increases the disk capacity and data-transmission speed, provided that the disk rotation speed remains the same. Hard disk capacity tends to double each year.
The data-access time includes the interval needed to position the head to the required track and the latency (the wait for the needed sector to appear under the head). The latency depends on the rotation speed.
For now, hard disks with a rotation speed of 7,200 rpm, 2 MB cache memory, and a capacity of 120 GB to 180 GB are the optimal choice for desktop PCs.
The most common models have a parallel ATA interface (i.e., IDE, EIDE, or ATAPI) with a data-transmission speed of 100 MB/sec. However, these are being replaced by the Serial ATA interface, which ensures a transmission rate of 150 MB/sec.
Hard disks have low overclocking potential. Acceleration of more than 20% may result in data loss, even under conditions of adequate cooling. This risk and the possibility of disk failure indicate that it is not wise to overclock hard disks.