What is SCSI?

Small Computer System Interface (SCSI) is a fast and strong  interface technology used in computer components such as hard drives, optical drives, scanners and tape drives. It is a faster but more expensive interface technology than IDE (Integrated Drive Electronics). IDE technology is built into motherboards while SCSI card  must have to be added into an internal PCI (Peripheral Component Interconnect) slot  by purchasing a SCSI controller for getting the advantage of  SCSI technology.  

The advantage of  SCSI  over  IDE  is that  it is  faster and stronger technology than IDE, and can be  connect 15 or more devices in  a  daisy  chain. The controller recognizes each device by  its  SCSI ID that  makes it more  flexible.

SCSI devices are usually used in servers that's  why it is  usually made to higher standards and carry longer warranties than IDE drives of comparable capacity. SCSI can be a great choice for a server when it is associated with a RAID as an additional drive.