Q. What is Small Computer Systems Interface?

The other well-liked way is to connect a disk drive to a PC by a SCSI interface. Common drive choice for high-end workstations or servers with drive capacities varies from 100MB to 20GB and rotation speed 7200RPM. It is a ordinary I/O interface between adapter and disk drives or any other peripheral it implies that CD-ROMs drives, tape drives, printers etc. 

SCSI (pronounced 'scuzzy') is an important and interesting variation of separate device controller idea for each device. It employs a generic device controller (known as SCSI controller) on computer system and permits any device with an SCSI interface to be directly associated to SCSI bus of SCSI controller. SCSI interface of a device comprises all circuitry that device needs to operate with computer system.

As shown in Figure below a SCSI controller connects directly to computer bus on one side and controls another bus (known as SCSI bus) on other side. Because SCSI controller is connected to computer's bus on one side and to SCSI bus on other side it can be communicated with processor and memory and can also control devices associated to SCSI bus. SCSI bus is a bus designed for associating devices to a computer in a uniform way.  

These drives have fast access time and high data rates however are expensive. One benefit of these drives is that a single SCSI controller can communicate concurrently with up to seven 16-bit SCSI devices or up to 15 wide or Ultra-Wide devices. Every device should be assigned a unique SCSI identification between 0 and 7 (or 15).

Figure: SCSI Drive Interface Standards