From: wlsmith@valve.heart.rri.uwo.ca (Wayne Smith)
Subject: Re: IDE vs SCSI
Organization: The John P. Robarts Research Institute, London, Ontario
Nntp-Posting-Host: valve.heart.rri.uwo.ca
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In article <1qk7kvINNndk@dns1.NMSU.Edu> bgrubb@dante.nmsu.edu (GRUBB) writes:
>>point of view, why does SCSI have an advantage when it comes to multi-
>>tasking?  Data is data, and it could be anywhere on the drive.  Can
>>SCSI find it faster?  can it get it off the drive and into the computer
>>faster?  Does it have a better cache system?  I thought SCSI was good at
>>managing a data bus when multiple devices are attached.  If we are
>>only talking about a single drive, explain why SCSI is inherently
>>faster at managing data from a hard drive.

>IDE:  Integrated Device Electronics 
> currently the most common standard, and is mainly used for medium sized 
> drives. Can have more than one hard drive. Asynchronous Transfer: ~5MB/s max.

Why don't you start with the spec-sheet of the ISA bus first?
You can quote SCSI specs till you're blue in the face, but if they
exceed the ISA bus capability, then what's the point?

Who says IDE is limited to 5 megs/sec?  What about VLB-IDE?  Does anyone
know how they perform?

>So at its LOWEST setting SCSI-2 interface in Asynchronous SCSI-1 mode AVERAGES 
>the through put MAXIMUM of IDE in asynchronous mode.  In full SCSI-2 mode
>it blows poor IDE out the window, down the street, and into the garbage can.

As implimented on what system?  

>The problem becomes can the drive mechanisim keep up with those through put
>rates and THAT is where the bottleneck and cost of SCSI-2 comes from.  NOT
>the interface itself but more and more from drive mechanisims to use the
>SCSI-2 through put.  

Given the original question (SCSI used only as a single hard drive
controller),  is it then necessary to get a SCSI drive that will do
at least 5, maybe 10 megs/sec for the SCSI choice to make any sence?
What does a 200-400 meg 5 megs/sec SCSI drive cost?

>The cost of SCSI interface is a self fulliling
>prophisy: few people buy SCSI because it is so expencive for the PC, which
>in turn convices makes that mass producing SCSI {which would reduce its
>cost} is unwarented, and so SCSI is expencive. {That is the effect of the
>Rule of Scale: the more items sold the less EACH item has to bare the brunt
>the cost of manufacture and so the less each item has to cost}

The original CGA cart back in '84 was $300.  I think the original EGA card
(or PGA?) was $800.  SCSI has stood relatively alone in not coming down
in price, mainly because we're talking about PC's and not Sun's or Sparc
or SGI or (name your favorite unix workstation).  That is, after millions
of PC buying decisions over the years, SCSI has had plenty of time to
come down in price.

I won't argue that the SCSI standard makes for a good, well implimented
data highway, but I still want to know why it intrinsically better
(than IDE, on an ISA bus) when it comes to multi-tasking OS's when
managing data from a single SCSI hard drive.
