The different types of SCSI interfaces are listed below:
- SCSI-1: Uses an 8-bit bus, supports data transfer speeds of 4 MBps.
- SCSI-2: Uses a 50-pin connector instead of a 25-pin connector, and supports multiple devices. It is one of the most commonly used SCSI standards. Data transfer speeds are typically around 5 MBps.
- Wide SCSI: Uses a wider cable (168 cable lines to 68 pins) to support 16-bit data transfers.
- Fast SCSI: Uses an 8-bit bus, but doubles the clock rate to support data transfer speeds of 10 MBps.
- Fast Wide SCSI: Uses a 16-bit bus and supports data transfer speeds of 20 MBps.
- Ultra SCSI: Uses an 8-bit bus, supports data rates of 20 MBps.
- SCSI-3: Uses a 16-bit bus, supports data rates of 40 MBps. Also called Ultra Wide SCSI.
- Ultra2 SCSI: Uses an 8-bit bus, supports data transfer speeds of 40 MBps.
- Wide Ultra2 SCSI: Uses a 16-bit bus, supports data transfer speeds of 80 MBps.
- Ultra3 SCSI: Uses a 16-bit bus, supports data transfer rates of 160 MBps. Also known as Ultra-160.
- Ultra-320 SCSI: Uses a 16-bit bus, supports data transfer speeds of 320 MBps.
- Ultra-640 SCSI: Uses a 16-bit bus, supports data transfer speeds of 640 MBps.
While SCSI is still used for some high-performance equipment, newer interfaces have largely replaced SCSI in certain applications. For example, Firewire and USB 2.0 have become commonly used for connecting external hard drives. Serial ATA, or SATA, is now used as a fast interface for internal hard drives.