(Small Computer System Interface) Pronounced "scuzzy." SCSI is a hardware interface for up to 15 peripheral devices attached to a single PCI board called a "SCSI host adapter" that plugs into the motherboard. SCSI devices were popular in the mid-1980s and 1990s for two reasons. SCSI disks were known to be very robust and were used in servers and storage arrays. SCSI was also a way to add several peripheral devices to personal computers.|
SCSI Is a Mini-LAN
SCSI uses a bus structure and functions like a mini-LAN connecting 16 devices, but the host adapter counts as one device. SCSI allows any two devices to communicate at one time (host to peripheral, peripheral to peripheral).
Host adapters are also available with two controllers that support up to 30 peripherals. Introduced in 1986 and originally developed by Shugart Associates (see SASI), SCSI is widely used in servers, mainframes and storage area networks (SANs).
The Daisy Chain
SCSI peripherals are daisy chained together. Each device has a second port used to connect the next device in line. An earlier advantage of using SCSI in a desktop PC was that a scanner and several drives (CD-Rs, Zip, hard disks, etc.) could be added to one SCSI cable chain. However, this became less important since the advent of the USB interface. For more details, see SCSI signaling.
RAID Was Originally SCSI
Until the late 1990s, SCSI hard disks were the only ones used in RAID configurations for improved performance or fault tolerance. Since the advent of IDE RAID controllers, SCSI and IDE have become more equalized, although SCSI continues to be the drive interface of choice in the server market. See SCSI signaling, SCSI connectors, RAID, SAS and SCSI switch.
The advantage of SCSI is that several peripherals can be daisy chained to one host adapter, using only one slot in the bus. For more details about SCSI specifications, signaling and connectors, see