Path: utzoo!dciem!array!colin
From: colin@array.UUCP (Colin Plumb)
Newsgroups: comp.periphs.scsi
Subject: Re: Is SCSI-2 ARLL?
Message-ID: <1976@array.UUCP>
Date: 18 Jun 91 21:57:51 GMT
References: <1991Jun18.001914.21305@sciences.sdsu.edu>
Organization: Array Systems Computing, Inc., Toronto, Ontario, CANADA
Lines: 21

In article <1991Jun18.001914.21305@sciences.sdsu.edu> add@sciences.sdsu.edu (James D. Murray) writes:
>
>	I'd like to know if the SCSI-2 spec defines the data encoding method
>to be used with SCSI drives.  SCSI drives use RLL encoding, but do they
>ever use ARLL encoding?  How about drives for use with SCSI-2 systems?

No SCSI spec (SCSI-1 or SCSI-2) define in any way the data encoding.
You could have a genie in there writing in Babylonian cuneiform on clay
tablets and conform to the letter of the SCSI spec, if you could get
him working fast enough to avoid timeouts.  All you have to have is a
bunch of blocks that can be read or written with a consistent number of
bytes each.

Because they aren't handicapped by a user-visible encoding (unlike
ST-506 and its ilk), SCSI drives (even where they're so staid as to use
horizontally magnetised, multi-layer discs for media) show more
variety.  MFM (also known as (1,3) RLL) is used, but the RLL used by
so-called "RLL controllers" for IBM PCs, namely (2,7) RLL is also used, and
(1,7) RLL is very popular.
-- 
	-Colin