Re: SCSI disks

tzeruch@ceddec.com
Mon, 2 Jun 1997 16:30:47 -0400


On Mon, 2 Jun 1997, W. Reilly Cooley wrote:

> I hate to continue to beat this subject into the ground, but exactly what are
> SCSI hard drives considered to the superior to IDE? According to the fellow
> who wrote "Upgrading and Repairing PCs" (who, as a PC technician, I don't
> wholly trust), SCSI hard disks a mostly IDE disks with an additional SCSI
> interface, (ie, the head-disk-assembly is the same, and most of the control
> electronics.) Does SCSI provide additional commands which permit finer
> tuning and/or error prevention/correction than IDE?
>
> It seems to be generally considered that SCSI is superior to IDE, but from
> this guy's writing (excepting for multiple devices on the SCSI bus or really
> fast HDs) SCSI provides no benefit. Pls. someone cursorily clarify.

It depends on what you do, but a very, very brief explanation:

I don't think IDE has disconnect/reconnect yet, and definately not on
CDROM drives, so when you access your CD, you cannot transfer data from
your disk. IDE is slowly adding these features, so some of this may be
dated, but SCSI has had multitasking features for years.

With SCSI, I can write data to my CDwriter from a hard disk connected to
the same bus, and it can multitask and thus interleave swap file updates
with the file reads. When I read from my CD, the read request is queued
and I can do things with my hard drive while the seek is happening on the
CD, and transfer the data from the CD when it is ready.

A single user system used mainly in a single-tasking mode won't see much
benefit (and they would not benefit from SMP).