14-07-2011, 12:24 PM
SCSI SEMINAR.pptx (Size: 298.63 KB / Downloads: 53)
INTRODUCTION
Small Computer System Interface or SCSI (pronounced scuzzy), is a set of standards for physically connecting and transferring data between computers and peripheral devices.
The SCSI standards define commands, protocols, and electrical and optical interfaces.
SCSI is most commonly used for hard disks and tape drives, but it can connect a wide range of other devices, including scanners and CD drives.
SCSI is an intelligent, peripheral, buffered, peer to peer interface.
SCSI interfaces provide for faster data transmission rates (up to 80 megabytes per second) than standard serial and parallel ports.
We can connect many devices to a single SCSI port. Thus SCSI is really an I/O bus rather than simply an interface.
Up to 8 or 16 devices can be attached to a single bus.
The SCSI protocol defines communication from host to host, host to a peripheral device, peripheral device to a peripheral device.
The Symbios Logic 53C810 chip is an example of a PCI host interface that can act as a SCSI target.
HISTORY
SCSI was derived from "SASI", the
"Shugart Associates System Interface", developed in 1978 and publicly disclosed in 1981.
Larry Boucher is considered to be the "father" of SASI and SCSI due to his pioneering work first at Shugart Associates and then at Adaptec.
The committee documenting the
standard would not allow it to be named after a company.
So they decided to name the standard
“Small Computer System Interface”.
ENDL's Dal Allan pronounced the new acronym as "scuzzy"
SCSI INTERFACES
There are 3 main types SCSI interfaces:
Parallel SCSI
Serial SCSI
iSCSI
PARELLEL Scsi INTERFACES
OTHER SCSI INTERFACES
SCSI CABLING
Traditional parallel SCSI
Serial attached SCSI
Internet small computer system interface
USB attached SCSI
SCSI COMMAND PROTOCOLS
In SCSI terminology, communication takes place between an initiator and a target.
There are 4 categories of SCSI commands:
N (non-data)
W (writing data from initiator to target)
R (reading data)
B (bidirectional).
There are about 60 different SCSI commands in total, with the most common being:
Test unit ready
Inquiry
Request sense
Send diagnostic and Receive diagnostic results
Start/Stop unit
Read capacity
Format unit
SCSI Read format capacities
Read (four variants)
Write (four variants)
Log sense
Mode sense
Mode select
HOW SCSI WORKS?
SCSI uses a protocol method to transfer data between devices on the bus.
It is a circular process which starts and ends up in the same layer.
The protocol layers are referred to as "SCSI bus phases".
The SCSI bus can be in only one phase at a given time.
These phases are:
Bus Free
Arbitration
Selection
Message Out
Command Out
Data Out/In
Status In
Message In
Reselection
SCSI DEVICES BEING USED by
The SCSI devices currently is being used by various companies.
Some of these companies are:
NCR Corporation
Adaptec
Optimem
Amiga
Apple Macintosh
Sun Microsystems