What the hell is...

[Mad]

(Small Computer System Interface) Pronounced "scuzzy." SCSI is a hardware interface that allows for the connection of up to 15 peripheral devices to a single PCI board called a "SCSI host adapter" that plugs into the motherboard. 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.

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 RAID, SAS and SCSI switch.

Google it, you dim witted ape.