Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!elroy!cit-vax!mangler
From: mangler@cit-vax.Caltech.Edu (Don Speck)
Newsgroups: comp.periphs
Subject: Re: Request Advice on Learning about ESDI
Summary: ESDI vs. SMD
Keywords: hard disk esdi interface
Message-ID: <9914@cit-vax.Caltech.Edu>
Date: 6 Mar 89 04:57:07 GMT
References: <6778@thorin.cs.unc.edu> <27019@sgi.SGI.COM>
Organization: California Institute of Technology
Lines: 15

ESDI and SMD sound very similar; all of the things that were
said about ESDI also apply to SMD drives.  The main differences
seem to be:
    a)	distance - SMD uses differential transmission on all signals so
	that it can extend to 50 feet, necessitating wider connectors;
    b)	SMD controllers often don't support anything beyond minimal
	functionality (no TAG4/TAG5, limited transfer rates, etc).

Why is SMD used only for 8-inch and larger drives?  (I can see how
ESDI's 10-foot cable limits it to 5-1/4 or smaller drives).

Are there interface protocol converters that let SMD controllers
run ESDI drives?  It seems like it should just be some latches
and differential drivers/receivers.  Most of the signals even
have the same name!