Advantages of Scsi
Transcript of Advantages of Scsi
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The following are advantages of the small computer system interface
(SCSI):
1. 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.
2. SCSI peripheral devices of the same type have similar characteristics
(this makes it easy to replace old devices with new ones).
3. SCSI peripheral devices are intelligent and independent: a controller
is built onto each SCSI device. This allows the computer to do other
work.
4. 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.
5. SCSI is fast (10 megabytes (MB)/second on 8 bit bus, 20 MB/second
on 16 bit bus).
6. 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 onSCSI 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/Odevice 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.
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• 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) simultaneously.
SCSI (Small Computer Systems Interface) was designed initially to be a
jack-of-all-trades kind of interface. I may repeat some of what has already
been said for the sake of making my answer as complete as I can.
Advantages:
1. SCSI can handle a wide variety of devices: hard drives, scanners, plotters,
CD drives, and the list goes on.
2. A SCSI controller can communicate with up to 7 or 15 devices depending
on the version. I am sure work is being done to add more.
3. It is often easier to install and setup a SCSI device than with many other
device interfaces. (This comment is not limited to the SCSI vs. IDE issue.
See Advantage #1 for the scope of what I mean by "device." I also say it is
"often easier," not "universally easier.")
4. SCSI controllers and devices are intelligent, they have microcontrollers, if
not full blown processors, inside them. They do not require software-base
contoller drivers like some Windows devices, putting less load on the CPU.
5. SCSI has proven itself to be a good platform for moving and storing large
amounts of data. Recent developments with SCSI have focused onexploiting this feature even further.
6. Newer SCSI devices and controllers are supposed to be backward
compatible with older SCSI devices and contollers. (from my own personal
experience, this is about 95% true)
7. Recent SCSI contoller and devices currently offer the highest through-put
for any peripheral connection scheme currently available.
8. SCSI drives are, on the whole, more reliable than ATA/IDE drives.
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