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From: emmo@moncam.co.uk (Dave Emmerson)
Newsgroups: comp.periphs
Subject: ESDI and SCSI2
Keywords: SCSI synchronous disk drives
Message-ID: <252@marvin.moncam.co.uk>
Date: 1 Aug 89 11:15:14 GMT
Organization: Monotype ADG, Cambridge, UK
Lines: 30

Perhaps I'm just displaying my ignorance in public, but personally
I can't see that these huge transfer rates are of much use to Joe
Public, since he still has to use DRAMs for any sizeable area of
memory on the grounds of cost.
Sure, he may have *some* fast SRAM in his system, probably only for
the graphics, but the limiting factor in most *affordable* machines
isn't going to be the disk's burst rate, it'll be the cycle time of
the target memory. Byte for byte, I'd guess that SRAM costs 10x DRAM,
and more for the very fast stuff. We already have the situation where
stuffing faster processors into a system produces only a small 
improvement in performance because of the wait states needed to make
use of even the fastest DRAMs. Anybody like to guess (quote?) the
price of 4Mbytes of 35nS SRAM for a system? Compare it with my 
guestimate of 450 dollars for 100nS DRAM on ours. It seems that every 
time there's an improvement in processor speed/memory speed/memory size/
media size/media transfer rate, there follows a corresponding decrease
in the efficiency with which we use it. Think back to what you were
almost happy with 10 years ago. However did you manage?
Oh yes, they'll improve, no doubt one day we'll get 25nS DRAMs free
with our wheatie flakes, but till then the fast disk drive manufactors
will have the same limited market as the fast processors, strictly
where performance overrides almost any cost considerations.
The wider transfer bus isn't just smart, it's the only affordable,
workable solution for most of us. As such I welcome it, but I can't
get all starry-eyed over the 8 bit performance claims, it's difficult
to sustain 3Mb/sec, let alone 5!

-Standard disclaimer-

Dave E.