Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!xanth!mcnc!ncsuvx!ece-csc!ncrcae!ncrlnk!ncrwic!encad!entec!jlohmeye
From: jlohmeye@entec.Wichita.NCR.COM (John Lohmeyer)
Newsgroups: comp.periphs
Subject: Re: SCSI interfaces
Message-ID: <317@entec.Wichita.NCR.COM>
Date: 28 Jan 89 01:37:03 GMT
References: <1138@naucse.UUCP> <5340003@hpfcdc.HP.COM>
Reply-To: jlohmeye@entec.UUCP (John Lohmeyer)
Organization: NCR Corporation, Wichita, Kansas
Lines: 27

In article <5340003@hpfcdc.HP.COM> rjn@hpfcdc.HP.COM (Bob Niland) writes:
>The MAC computers use a 25-pin DB25 (RS-232C style) connector instead of
>the standard ALT-2 50-pin, but other than that, I am not certain of how
>they vary from ANSI.  I'll ask our SCSI guru to respond.

While the MAC does have a DB25 on the MAC, it uses miniature ribbon
connectors (SCSI standard) on the peripheral boxes.

There are several ways that the MAC deviates from "typical" SCSI (I didn't
say "standard"). A few that I can think of off the top of my head are:

 1. It doesn't terminate the bus at the MAC end of the cable.
 2. It doesn't handshake bytes properly (this may have been fixed).
 3. It won't boot from a SCSI disk that reports unit attention after
    power-up (required by the SCSI standard).

(Actually, all of the above are violations of the SCSI standard.)  In addition
to these problems, Apple didn't go out of its way to make it easy to add on
third-party SCSI devices. (Nor did they really try to block add ons.)

Apple recognizes that they have some problems and somewhere I have a copy of
an Apple application note that details what the problems are and how to
work around them.  I think they are making a real effort to improve the
situation.

John Lohmeyer, NCR Corp.
j.lohmeyer@Wichita.NCR.COM