Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!usc!apple!amdahl!drivax!liberato
From: liberato@drivax.UUCP (Jimmy Liberato)
Newsgroups: comp.sys.ibm.pc
Subject: Re: MFM, RLL, SCSI drives
Keywords: RLL SCSI
Message-ID: <256BAE8C.79F@drivax.UUCP>
Date: 23 Nov 89 08:47:08 GMT
References: <286@marvin.moncam.co.uk>
Reply-To: liberato@drivax.UUCP (Jimmy Liberato)
Organization: Digital Research, Inc., Monterey, California
Lines: 25

emmo@moncam.co.uk (Dave Emmerson) writes:


>There's been a lot of slagging-off of RLL drives, and praising of SCSI
>(and acceptance of MFM as cheap but reliable). I've just re-read the
>much vaunted Quantum PRO80S's manual to confirm my suspicions, and it's
>TRUE, section 2, page 1 of the Installation Manual for this Embedded
>SCSI drive has an entry 
>Encoding scheme		RLL 2,7

>Pick the bones out of that one then!

It wouldn't be fun if it wasn't confusing!  I don't think the SCSI controller
chip knows or even cares what kind of physical format the DMA controller/data
sequencer chip is encoding the bit stream as.  One's logical, the other is 
physical. Yeah, I know, an oversimplification but isn't that the magic of
SCSI, its transparency?  Rather, the transparency to the SCSI bus of the more
physical things like media defects, interleave, and format?

I defer to the SCSI gurus out there (or to anyone who has actually slogged
through ANSI X3T9.2/82-2).  I do know that most of the high-end embedded
SCSI drives are RLL 2,7.  What do the others use, something proprietary?

--
Jimmy Liberato   ...!amdahl!drivax!liberato