Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!mcsun!ukc!edcastle!as
From: as@castle.ed.ac.uk (A Stevens)
Newsgroups: eunet.micro.acorn,comp.sys.acorn
Subject: Re: Installing Hard Disks
Keywords: Hitachi Hard Disk
Message-ID: <7929@castle.ed.ac.uk>
Date: 19 Jan 91 13:14:20 GMT
References: <1991Jan18.151427.23894@cns.umist.ac.uk>
Organization: Edinburgh University Computing Service
Lines: 47

In article <1991Jan18.151427.23894@cns.umist.ac.uk> vanaards%t7@uk.ac.man.cs writes:
>
>  I've got an old 5 1/4"  13MB (10MB) Hard disk drive, taken from an old
>Sharp MZ5600-A. Does anyone know whether or not it is possible for this
>drive to be used in the Archimedes - I have a SCSI i/f and the ST506 i/f.
>The Drive has a make code DK503.
If it has a proper ST506 interface and you can find out heads/sectors/
cylinders - Yes!  (I would be very surprised if an old 10M drive were 
not ST506).

>
>  Secondly, what drives can I use with the Archimedes. When looking down
>lists of Hard disks in the PCW, you generally see ST numbers, and possibly
>type of drive such as RLL,SCSI,IDE, etc, how do I know which will work with
>the Archimedes - I've only seen one ST506 !

The built-in A400 interface will handle winchesters that use MFM encoding
over the ST506 (sometimes called ST421 I think) interface.   SCSI drives
*should* work with a SCSI interface, but I gather there are sometimes
annoying deviations in the precise way drives respond to commands over
the SCSI bus.  I am no expert on this latter point.

>  That leads onto my final question about Hard Disks, what makes an RLL drive
>different from a SCSI drive - in terms of internal Hardware ? I have previously
>assumed that the RLL has an interface which compresses the data going to the
>disk, and this i/f sits as a front end to the standard drive i/f which 
>actually does the controlling of the heads.
> 

SCSI drives attach to a proper interface bus over which they accept quite high
level commands of the ``get me this sector'' kind.   RLL drives
are just drives that use the old hacky ST506 interface (named after the
Shugart drive that introduced it), but with the data recorded
onto the disk (and sent to the controller which does the bit level clock
separation and decoding) using the fancier RLL encoding scheme rather than
the original MFM.

Internally - at the platter and analogue level - RLL and SCSI drives
differ not one whit, it is only the interface board that differs.
Mind you not all drive mechanisms can do RLL - it requires rather
more bandwidth than the simpler MFM encoding scheme.

Wether or not a SCSI drive uses MFM or RLL or whatever internally
is invisible due to the high level nature of the SCSI bus.


Andrew