See also: IDE
Acronym: Small Computer System Interface
A type of interface in computers that was the original solution to the slow connection speed of many peripherals such as scanners and internal/external hard drives. Although USB and Firewire provide a useful alternative, SCSI (pronounced Skuzzy) is still known for its high quality, speed and price.
There are various types of SCSI: SCSI, SCSI2 (ulltra-wide) and SCSI3 each having their own benefits, especially regarding performance and also the connector. Because of this, one cannot use a SCSI3-type harddisk on a SCSI2-type SCSI card although there are connectors which circumvent this. Eg. SCSI2 to SCSI3 converter, SCSI2 to IDE converter. These days SCSI2 and SCSI3 are common.
SCSI often needs its own individual card to operate peripherals and drives. This card can be on-board or a PCI add-on. Speed and connectors often vary in size.
One alternative to SCSI is RAIDed IDE hard drives but SCSI storage media is also often used in a RAID configuration. Currently (august 2004) this is less expensive since (new) SCSI hard drives cost ~5 times more than one IDE hard drive of the same size. This means you can get a RAID5 setup for about the same price as one IDE drive. It is generally believed a SCSI drive has a longer life than an IDE one.
The value compared to lower-end hard drives has dwindled with the leaps and bounds made in storage size and with the raised bar in quality of lower-end hard drives. SCSI often needs its own individual card to operate peripherals and drives, also increasing its cost compared to IDE systems.