Difference between IDE and SCSI ??

Ben Kamen bkamen at benjammin.net
Sat Feb 2 21:12:15 UTC 2008

Some BIG items are being left out of the SCSI discussion...

So allow me to add:

Unlike IDE, SCSI was more geared towards PERIPHERAL integration into computer 

with IDE, you can (mostly) only hook up storage devices... but with SCSI,
you could hook up  just about anything. Scanners, Network Interfaces, Drives, 
Tape backups, the list goes on and on becauce SCSI that's what SCSI was designed 

Now, I don't know if I would say IDE was around that much longer than SCSI as
a defined standard. But, the SASI interfaces and other MF style drives had some
sort of similar setup where the drive was dumb and needed some sort of controller.

I still have the SCSI -> MFM controllers for my Atari's back in the mid-80's
(which when they were cheap for Atari in the mid-80's, that leads me to believe
SCSI was around a bit longer than IDE as a "standard").

In fact, on my Atari, over 1 SCSI bus, I had hard drives, tape drives and 
Syquest Removable storage as well as CD-ROM's and a scanner. All on 1 system!

Original SCSI was limited to 8 devices (3 bit addressing with 1 being taken up 
by the "host adapter) leaving 7 more for devices (or other hosts! do that with IDE!)

SCSI Wide used 4 bit addressing (16 devices) and a 16bit data bus effectivly
doubling the data tranfer rate.

In the beginning, SCSI was always faster than IDE because the intelligence of 
the drives (remember, IDE tends to be dumb as it's controlled by the host), that 
lent the drives to be more expensive. So think "server" and thus smarter, more 
expensive also demanded "faster".

Eventually IDE caught up because the demand required it and the scale of 
production brought the price of the mechs down (which is why they're so cheap 
these days even though as an interface SCSI is better - but the point is moot
for the typical home/biz user).

Now, I've had machines with multiple SCSI host adaptors (they aren't 
"controllers" because the peripherals control themselves. The computer is more
a peer in this relationship) where I've had 6 or 7 devices hooked to a single
SCSI Fast/Wide bus.

Good stuff SCSI was. Highly underused but never overrated.


Ben Kamen - O.D.T., S.P.
Email: bkamen AT benjammin DOT net       Web: http://www.benjammin.net
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