Date   : Thu, 25 Dec 1997 11:15:27 +0000
From   : Mike Tomlinson <jasper@...>
Subject: Re: BBC Hard discs

In article <1997122422190866447@...>, Mike Mallett
<mike.mallett@...> writes

>I was confused about the drive - some people have told me it was
>MFM and others said RLL.

An RLL controller simply stuffs more data onto the disc with less
clocking information than MFM uses.  

Most newer MFM drives could be reformatted on an RLL controller to gain
the extra capacity, a bit like drilling the extra hole in a 720k floppy
to format it to 1.44.  Most of the time you get away with it, but it
depends on the quality of the disc and shouldn't really be done if you
care about your data.

So, as you are in the opposite situation, having an RLL drive on a less
demanding MFM controller, there is no need for concern.

>If you are saying the controller is MFM I could attach any MFM drive ?

Yes.  I used a wide range with no problems.  You will need to format it
with SuperForm.  The only drive I had trouble with was a 20Mb unit out
of an Amstrad 1512 - actually badged Amstrad, though I doubt they really
made it - which developed random bad sectors using the Beeb but
formatted and operated perfectly on a PC.

>I have another smaller drive (not to hand so I can't find the spec) 
>which I can swap
>with the above drive. Would it be possible to run BOTH drives off the 
>same controller ?

Yes.  I'd suggest not trying if you have never set two MFM drives up on
the same controller before.  You need a 34 way cable with a twist -
/*and this twist is in a different place to the twist on a PC floppy
cable, which won't work*/, another 20 way cable,  and to set both drives
to id 1, and to ensure only the drive at the end of the cable is
terminated, and to ensure your power supply is capable of running the
extra load, and to have the correct paramters for the second drive to
plug into Superform, etc.

>My main drive is partitioned to run ADFS and DOS-Plus (for the 512  
>80186 board).
>I also have a Z-80 co-pro but so far I have been told it is not possible to run
>CP/M from the hard disc.

I understand that is correct - Acorn CP/M doesn't support hard discs.
The Torch Z80 card does, however.

-- 
Mike Tomlinson