Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!decwrl!sgi!markb@denali.SGI.COM
From: markb@denali.SGI.COM (Mark Bradley)
Newsgroups: comp.periphs
Subject: Re: Request Advice on Learning about ESDI
Summary: ESDI VS SMD
Keywords: hard disk esdi interface
Message-ID: <28031@sgi.SGI.COM>
Date: 6 Mar 89 21:02:55 GMT
References: <6778@thorin.cs.unc.edu> <27019@sgi.SGI.COM> <9914@cit-vax.Caltech.Edu>
Sender: daemon@sgi.SGI.COM
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 33

In article <9914@cit-vax.Caltech.Edu>, mangler@cit-vax.Caltech.Edu (Don Speck) writes:
> 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:
> 
> 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).

SMD is not just for large drives anymore.  There were some 5 1/4"
drives announced last fall that will come with SMD (and other)
interfaces.
> 
> 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!

It is more than just an electrical interface that we are talking about
here.  ESDI has a lot more thought built into it than SMD.  Things
like request configuration, vendor ID, vendor unique things, etc.
make it easier to integrate new drives.  Also, ESDI will be going to
24 MHz before long, too, so why not just get ESDI controllers?  I am not
aware of any SMD to ESDI converters, but I agree that it would not
take rocket science to allow at least base level functionality in such
a beast.

						markb

--
Mark Bradley				"Faster, faster, until the thrill of
IO Subsystems				 speed overcomes the fear of death."
Silicon Graphics Computer Systems
Mountain View, CA			     ---Hunter S. Thompson