SCSI stands for "Small Computer Systems Interface". It is a standard for parallel data transfers between a computer and its devices on a so-called [SCSI bus]?. It was re-named from the proprietary [Shugart Computer Systems Interface]? when a number of other companies also decided to adopt the same standard. Since then, SCSI has been developed as an industry-wide standard. |
SCSI stands for "Small Computer Systems Interface". It is a standard for parallel data transfers between a computer and its devices on a so-called [SCSI bus]?. It was re-named from the proprietary [Shugart Computer Systems Interface]? when a number of other companies also decided to adopt the same standard. Since then, SCSI has been developed as an industry-wide standard. |
Bus speed (MB/s) |
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Bus speed (MBytes/s) |
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iSCSI | limited only by IP network | N/A | N/A | ?? |
On the computer side there must be a SCSI adapter/controller which controls the data transfer on the SCSI bus. The most popular devices on a SCSI bus are hard disks but it is also possible to connect scanners, CD-ROMs, CD writers, DVD-ROM?s, etc.
SCSI comes in several flavours (standards):
Each SCSI device must be configured to have a unique SCSI ID on the bus.The SCSI adapter needs an ID for itself, too, as it appears as a device on the bus it controls.
The SCSI bus must be terminated with a terminator (there are both active and passive terminators) at both ends of the bus. Wrong termination is a very common problem with SCSI installations.
It is possible to convert a wide bus to a narrow one, with wide devices closer to the adapter. To do this properly requires a cable which terminates the wide part of the bus. This is sometimes referred to as a cable with high-9 termination.
In the past SCSI was very popular on all kinds of computers. Today, SCSI is mainly used on high-performance workstations or servers. Desktop computers and notebooks mostly use the cheaper ATA?/IDE interface instead of SCSI.
Many SCSI interfaces are now implemented over [Fiber Channel]?. However, Fiber Channel is generally only used in high-end systems, particularly RAID system attachments.
The newly introduced iSCSI? standard, an embedding of SCSI-3 over TCP/IP is expected by some to replace Fiber Channel in the long run, as commodity Ethernet data rates are currently increasing faster than Fiber Channel and similar disk attach technology data rates, and iSCSI can address both the low-end and high-end markets with a single commodity-based technology.
However, iSCSI preserves the basic SCSI paradigm almost unchanged.
See also:
Interface | Bus speed (MBytes/s) | Bus width (bits) | Max. cable length (meters) | Max. number of devices |
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SCSI | 5 | 8 | 6 | 8 |
Fast SCSI | 10 | 8 | 1.5-3 | 8 |
Wide SCSI | 20 | 16 | 1.5-3 | 16 |
Ultra SCSI | 20 | 8 | 1.5-3 | 5-8 |
Ultra Wide SCSI | 40 | 16 | 1.5-3 | 5-8 |
Ultra2 SCSI | 40 | 8 | 12 | 8 |
Ultra2 Wide SCSI | 80 | 16 | 12 | 16 |
Ultra3 SCSI | 160 | 16 | 12 | 16 |
iSCSI | limited only by IP network | N/A | N/A | ?? |