Xref: utzoo comp.unix.xenix:1538 comp.sys.ibm.pc:12215
Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!unisoft!gethen!farren
From: farren@gethen.UUCP (Michael J. Farren)
Newsgroups: comp.unix.xenix,comp.sys.ibm.pc
Subject: Re: a reply to ISC on 'clarifications'
Message-ID: <701@gethen.UUCP>
Date: 22 Feb 88 09:02:50 GMT
References: <795@vixie.UUCP> <783@bigtex.uu.net> <1667@van-bc.UUCP> <824@bigtex.uu.net> <1674@van-bc.UUCP> <231@braille.UWO.CDN>
Reply-To: farren@gethen.UUCP (Michael J. Farren)
Organization: There's Unix there in Oakland
Lines: 34
Keywords: mfm,rll,

In article <231@braille.UWO.CDN> kirk@braille.uwo.cdn (kirk reiser) writes:
>
>St-506, rll, and mfm are all terms used when talking about or working with
>hard drives.  There doesn't seem to be a lot of information abailable about
>the differences between these systems of disk formatting.

There is a lot of information available.  All you have to do is to read
the appropriate journals, technical magazines, or any good reference
on disk systems.  There's nothing secret about any of this, you just
have to do your homework.

>It would be nice
>to see a discussion about the various types of systems like this or some 
>references to where information can be obtained.

There has been a lot of discussion of this over time.  To reiterate,
ST-506 is the hardware interface to the disk drive, and specifies
among other things, how data is sent to the drive, how the drive is
controlled, and what sort of connectors are used.  Other interfaces
include SCSI, ESDI, and SMD.  Each is different, but the "standard"
IBM-PC interface is ST-506.

MFM and RLL are two different ways of encoding the data which is sent
to the disk.  RLL allows 50% more data to be put on the same amount
of disk space, but requires more sensitive electronics and a somewhat
higher-quality drive.  MFM is the "standard" scheme, used on almost
all 10 and 20 Megabyte drives.  RLL is used mostly in the 30 Megabyte
drive packages commonly available.


-- 
Michael J. Farren             | "INVESTIGATE your point of view, don't just 
{ucbvax, uunet, hoptoad}!     | dogmatize it!  Reflect on it and re-evaluate
        unisoft!gethen!farren | it.  You may want to change your mind someday."
gethen!farren@lll-winken.llnl.gov ----- Tom Reingold, from alt.flame