SCSI Explanation?

[Orcmonkey]

I'm looking for a basic explanation of SCSI technology, specifically in hard drives. All I know basically is that they are faster, and more expensive. What is the actual difference, what does SCSI mean? And... What do you need for a SCSI hard drive? I always notice when installing windows "If you need to install a driver for SCSI....." I assume then there is some sort of card for it? Thanks.

[TwoRails]

HI Orcmonkey,

Did you do a search on the forum? Toaster and others have recently posted several very excellent explainations.

TwoRails

PS: I say the above in a good way ! There is just a lot of info in some recent posts you will find enlightening!

[Toaster]

Howdy,
SCSI means "Small Computer Systems Interface".
SCSI has been around since the dawn of computers.
In any case, either a SCSI interface must be present to use SCSI devices.
SCSI is a "concurrent" device which permits "all" devices to function "cuncurrently".
SCSI, like IDE has some needs that must be filled.
Namely, cable lenght limitations , termination requirements and in some case drivers.
Current SCSI data rates exceed 320MB/sec and "common" SCSI devices are 80/160MB/sec.
There are 3 "primary" types of SCSI devices in use today.
They are:
SCSI-50 (50 pin connector)
SCSI-68
SCA-80 (unitized connector)

The SCSI "interface" varies as well dependant on age, the more common are:

SCSI-II- (upto 20MB/sec)
SCSI-III- (supports SCAM or auto configure)
SCSI/LVD- (low voltage differential)
Data rates of SCSI/LVD are at 320MB/sec.
SCSI-SE- Single ended. (common SCSI)
This interface is primarily with the 50 or 68 pin interface with data rates through 40MB/sec.

SCSI/SE/Ultra-
This "can" be any number of the above or a combination. Data rates are upto 320MB/sec.

SCSI-Differential (also called HVD)
Differential SCSI is not compatible with SE devices and is more often found on older server class/array systems.


Keep in mind this is "simplified".


Cable length maximums depend on the version of SCSI . Maximum cable lenghts start at 1 meter (about 3 feet).

[Orcmonkey]

You're right tworails, I probably should've searched before posting! Doh!

[Cricket]

Hi Orcmonkey,

There's several articles on SCSI here at PC Mech. Here's one of them: PC Mech: SCSI Interface

You can find the others by going to the main page and click on hard drives in the "Inside the Mech" column on the left side of the webpage.

Cricket

[Hpro]

One more important thing is that SCSI has it's own onboard CPU and if you use some of the real good SCSI Hardware cards even it's own RAM so it will not eat either CPU nor RAM of the system - whatever the controller is much more sophisticated than that of IDE
Hpro