Date   : Sat, 29 Jun 2013 14:37:49 +0100
From   : dl.harper@... (David Harper)
Subject: Master 512 disk images

The recent questions about using disk images with an emulated M512 have 
made me look at this set-up. (I have never really looked at it before at 
all.)

The Master 512 on BeebEm comes with the original (DOS-Plus 1.2) boot 
disk. Images of the newer versions of DOS-Plus (version 2.1 and indeed 
1.2a) have been available for some time at 
http://www.cowsarenotpurple.co.uk/bbccomputer/master512/system.html

However, trying to use these with BeebEm, I realised that the boot disks 
were not in the right format. I have now corrected this on the website, 
and provided a couple of new images. (Download the "Method 1" package if 
you want to try them out.) The new ones might work better with some disk 
image writers as well.

For those who are interested in details:

    The increment order for a Large ADFS disk is track-before-side. This
    means data on the disk is stored in the order:
         Sd0 Tr0, Sd0 Tr1, Sd0, Tr2, ... , Sd0 Tr79, Sd1 Tr0, Sd1 Tr1,
    ... , Sd1 Tr79

    An Acorn 640kb bootable DOS disk inherits its lowest level structure
    from ADFS, and so uses the same increment order.

    All other DOS disks (MS formats and the Acorn 800kb format) use the
    increment order side-before-track. So on such disk data is stored in
    the order:
         Sd0 Tr0, Sd1 Tr0, Sd0 Tr1, Sd1 Tr1, Sd0 Tr2, ... , Sd0 Tr79,
    Sd1 Tr79

    The data in the images of the 640kb disks was stored in
    track-before-side order. Strictly speaking this is "correct" for
    such disks. However BeebEm (as well as some disk reading and writing
    programs) assume a side-before-track order.

    The new versions of the images interleave the tracks so that they
    will read correctly in these programs.


David Harper