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From: tim@hoptoad.UUCP
Newsgroups: comp.periphs,comp.sys.mac
Subject: Re: Making a Mac talk SCSI to a Sun
Message-ID: <1821@hoptoad.uucp>
Date: Mon, 16-Feb-87 17:28:35 EST
Article-I.D.: hoptoad.1821
Posted: Mon Feb 16 17:28:35 1987
Date-Received: Tue, 17-Feb-87 19:13:12 EST
References: <2594@phri.UUCP> <1784@hoptoad.uucp> <540211194.20192@minster.UUCP>
Reply-To: tim@hoptoad.UUCP (Tim Maroney)
Distribution: world
Organization: Centram Systems, Berkeley
Lines: 40
Xref: watmath comp.periphs:211 comp.sys.mac:1327

In article <540211194.20192@minster.UUCP> martin@minster.UUCP (martin) writes:
>In article <1784@hoptoad.uucp> tim@hoptoad.UUCP (Tim Maroney) writes:
>>I believe there would be problems with having two SCSI masters.  A better
>
>No, SCSI (as opposed to SASI) was explicitly designed to allow any, or
>all, of the devices to be masters. If having two masters dosn't work, then
>one of the machines dosn't implement SCSI correctly (or completely!).

I am well aware of this; as I pointed out, the Mac does *not* implement SCSI
very well.  The SuperMac people replaced the SCSI Manager with their own
software and tripled performance (combined with a lower disk interleave, of
course) for the Dataframe XP drives.  I would be very surprised if it had
any debugged or real capabilities not exploited by the existing peripherals.

>I don't know about the implementations on the Sun, or the Mac, but all
>high performance (which I assume the Sun interface, at least is) interfaces
>should implement disconnect-reconnect to allow overlapped seeks, and
>this automatically gives one the multi-master capability (again so long
>as the software is not broken :-).

But this is the Sun, and both the Sun and the Mac would have to be "high
performance".  I don't know SCSI very well, but the disconnect-reconnect
sequence sounds like it may be exactly what the SCSI Manager lacks.

>	The review of the Mac+ in November '86 Byte states that the
>throughput of the SCSI interface is 320K bytes per second; does anyone
>know if it is really this slow? SCSI is rated at 10M Bits (= 1.25 M Bytes)
>per second, where is the factor of (almost) four going?

It is true; the reason they got away with it was that it was so much faster
than the HD20 and other pre-Mac Plus Mac hard disks, except the ones that
required major surgery.  The reason is bad software.  But SuperMac isn't
talking about what they fixed, and neither is anyone else who knows.
Perhaps we could all work it out here?
-- 
Tim Maroney, Electronic Village Idiot
{ihnp4,sun,well,ptsfa,lll-crg,frog}!hoptoad!tim (uucp)
hoptoad!tim@lll-crg (arpa)

Celibacy is just soft-core eunuchry.