The hard drive is a physical disc where the computer stores information for both you and your programs.

Hard drives are sometimes referred to as HDs or HDD. There are currently 4 types of HDs on the market. Each provides the basic needs for the user while some are more high performance with speed being the main goal.

ATA
(AT Attachment) drives vary in speed and are the basic connection type used by computers. ATA100 or ATA133 refer to the bandwidths allowed by the drive and the cable connecting them to the motherboard in Megabytes per second.

SCSI
(Small Computer System Interface) is another variation of drive available. Sometimes pronounced as "scuzzy" these drives are normally used in server based systems as they provide quick response times do to high RPMs, large bandwidths and the ability to chain together up to 16 drives on one cable.

SATA
or SerialATA is the latest connection available. SATA uses a cable that is about 1/8th the width as a normal ATA cable and supports bandwidth speeds up to 150 megabytes per second. This device also can require a special power connection at times but varies on the manufacturer. SATA II is the next step in speed providing up to a transfer rate of 300 megabytes per second.

SSD
or Solid State Drives are the newest form of hard drive available on the market. These drives do not use the typical platter and needle spin systems, instead the drive is comprised completely of memory sticks. Much like todays USB memory drives, only much more sophisticated. Currently these drives use a SATA interface and are considered the fastest in the world. Of course this also makes them extremely expensive. An 80GB SSD drives typically costs about $500 these days.

In general the faster the RPM of the drive or higher the bandwidth, the better the performance. If your current hard drive is 2-3 years old chances are installing a newer device will improve performance at that level.