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From: info-vax@ucbvax.ARPA
Newsgroups: fa.info-vax
Subject: Re: HSC50s
Message-ID: <3280@ucbvax.ARPA>
Date: Wed, 14-Nov-84 13:29:22 EST
Article-I.D.: ucbvax.3280
Posted: Wed Nov 14 13:29:22 1984
Date-Received: Thu, 15-Nov-84 03:31:16 EST
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Organization: University of California at Berkeley
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From: lou@aero3 (Lou Nelson (ISRO))

>Date: 12 Nov 1984 1252-PST (Monday)
>To: Bill Mitchell <whm%arizona.csnet@csnet-relay.ARPA>
>Cc: info-vax@sri-csl.ARPA
>Subject: Re: 8600 performance?
>
>Yeah, I have been puzzled by the emphasis on UNIBUS stuff myself.
>I asked a few DEC people about why they put an RA81, which is a 
>fine drive, which is a 2MB/s device, on a .5-.8MB/s UNIBUS.
>They said that those drives are part of the DSA and they want you
>to use the CI bus and cluster them together, and that the CI
>bus is 70 Mb/s and isnt unibus bound.  But then I pointed out that
>their file server, a HSC50 is an 11-based product and has the unibus
>in it as well, and the disks go thru an UDA50.  I asked what the
>difference was where the unibus bottleneck was, that its still
>a bottleneck.  They didnt know why, but they said they had a good
>reason.  Sigh.  I really like the RA81, its a great idea,
>but this unibus stuff is ridiculous.   Thats why I only use
>Eagles and Emulex massbus controllers (SI makes them too).
>Surely they arent planning a new line of PDP11 unibus
>products...

I was puzzled about this about a year ago and asked
a regional support guy and he pointed out that the data
paths in the HSC50 involved very fast bit-slice processors
and that the pdp11 was involved only in control.  He didn't know
if the horrendous disk drive port switching time was
finessed though.  I couldn't get the RA81s to work well and
switched to SI 9900s and Eagles also.