What is SCSI?

R. Kayne

SCSI is a type of interface used for computer components such as hard drives, optical drives, scanners and tape drives. It is a competing technology to standard IDE (Integrated Drive Electronics). While the less expensive IDE technology is built into motherboards, SCSI is a technology that must be added by purchasing a special controller. The SCSI card fits into an internal PCI slot, and the associated devices are then connected to this card.

SCSI is a type of communication interface used in computer components like a hard drive.
SCSI is a type of communication interface used in computer components like a hard drive.

This interface is a faster, more robust technology than IDE, and has traditionally been utilized in servers. Aside from speed, another great advantage over IDE is that the card can connect 15 or more devices in a daisy chain. The controller assigns each device its own ID, allowing for great flexibility towards expanding any system.

SCSI devices, particularly hard drives, are designed to be used 24/7 in addressing the needs of the server market. For this reason, the drives are usually made to higher standards and carry longer warranties than IDE drives of comparable capacity. However, the added speed and quality come at a price. SCSI components are significantly more expensive than their IDE cousins.

As the technology has evolved, different varieties have emerged with varying benchmark speeds. The various versions utilize different pin connectors. Therefore, it is important to match the right SCSI controller to the desired components. For example, if a drive is Ultra 320, a SCSI-I controller will not work with it. The controller must support Ultra 320 to be compatible. Following is a list of versions with the data transfer rates in megabytes per second (MB/sec):

SCSI-2, Fast SCSI (8-bit Narrow) to 10 MB/sec
Ultra (8-bit Narrow) 20 MB/sec
Ultra Wide (16-bit Wide) 40 MB/sec
Ultra2 (16-bit Wide) 80 MB/sec
Ultra 160 (16-bit Wide) 160 MB/sec
Ultra 320 (16-bit Wide) 320 MB/sec

For a server, SCSI can be a great choice for a RAID (Redundant Array of Independent Disks), as additional drives can be added as needed. If the pocketbook cannot afford a SCSI RAID or if, as in the case of an end-user, the technology is overkill, a SATA RAID is a good alternative at an affordable price.

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Discussion Comments


this was really helpful. thank you very much.


The Small Computer System Interface has a fast bus that can connect lots of devices to a computer at the same time. This includes hard drives, scanners, CD –ROM/RW drives, printers and tapes. --Joannna

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