The following are advantages of the small computer system interface
- Unlike other interfaces, when you interface with different device
types using SCSI, the interfacing is done through the same cable.
In a non-SCSI environment, devices such as a proprietary tape
controller, disk controller, and so on, must be used to connect
their respective devices to the system bus.
- SCSI peripheral devices of the same type have similar
characteristics (this makes it easy to replace old devices with new
- SCSI peripheral devices are intelligent and independent: a
controller is built onto each SCSI device. This allows the computer
to do other work.
- SCSI I/O is independent of the system bus. This allows peripheral
devices to work with different computer types, which preserves a
company's hardware investment.
- SCSI is fast (10 megabytes (MB)/second on 8 bit bus, 20 MB/second
on 16 bit bus).
- Multi-threaded operating systems, such as Windows NT, can take full
advantage of the multi-tasking capabilities of the SCSI bus.
For example, when a Windows NT thread requests to read a logical block
on SCSI disk 1, and at the same time, a second thread requests to write
some data to SCSI disk 2, the following may occur:
- The SCSI host adapter will process the first request made by
Windows NT executive by arbitrating the SCSI bus and making a
connection to disk 1.
- After the connection is made, disk 1 will disconnect and give up
the bus (bus free) so that other requests can be made by the host.
- The first thread will stop executing and will wait while the slow
I/O device completes a data transfer.
- As the seek is carried out on disk 1, the second thread request
will be processed in the same manner as the first, because Windows NT
can issue a "context switch" to allow for a thread of execution
while another is still being completed.
- Because the bus is free at this time, the host (initiator) will be
able to make a connection with disk 2. Disk 2 will then disconnect
and perform a write of some data to a logical location on the disk.
At the same time, disk 1 may still be seeking the block to read.
The two devices are therefore performing a task ( read, write)
Article ID: 103435 - Last Review: November 1, 2006 - Revision: 3.1
- Microsoft Windows NT Advanced Server 3.1
- Microsoft Windows NT Workstation 3.1