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Path: utzoo!attcan!uunet!labrea!decwrl!palo-alto!vixie
From: vixie@palo-alto.DEC.COM (Paul Vixie)
Newsgroups: comp.periphs,comp.sys.att,unix-pc.general
Subject: Re: Questions on SCSI device interfacing...
Keywords: SCSI, tape, hard drives, cabling, controllers, cost
Message-ID: <3549@palo-alto.DEC.COM>
Date: 22 Jul 88 19:35:50 GMT
References: <433@icus.UUCP> <704@hodge.UUCP>
Organization: DEC Western Research Lab
Lines: 19

In article <704@hodge.UUCP> rusty@hodge.UUCP (Rusty Hodge) writes:
# A raw SCSI drive usually has a 50-pin header connection.  The standard SCSI
# connection is a 50-pin Centronics.  The Macintosh folks use a DB-25.  Don't
# ask me to explain, but it works.

The 50-pin ribbon cables have ground on every other pin, which is common.  So
there are only 25 pins worth keeping if you don't care about horizontal
shielding between each pair of pins.

The Apple DB25 setup has a shield around all 25 pins, which is connected, at
the Centronics-to-DB25 connection, to the bus-bar of 25 grounds found in the
50-pin ribbon cable.

It sounds flinky but it works.
-- 
Paul Vixie
Digital Equipment Corporation	Work:  vixie@dec.com	Play:  paul@vixie.UUCP
Western Research Laboratory	 uunet!decwrl!vixie	   uunet!vixie!paul
Palo Alto, California, USA	  +1 415 853 6600	   +1 415 864 7013