Date   : Tue, 29 Apr 2003 07:48:53 -0700
From   : Angus Duggan <angus.duggan@...>
Subject: Re: BBC Micro Games Copy Protection

John Kortink writes:
>On Tue, 29 Apr 2003 09:35:46 +0100, Richard Talbot-Watkins wrote:
>
>>The original Acornsoft disc version of Elite didn't run on a Master.  It
>>didn't even get as far as the "Saturn made out of dots" screen; instead it
>>just thrashed the disc drive head repeatedly in a rather alarming way.  I
>>assume its protection methods were not Master compatible for some reason.
>>Does anyone know why?
>
>I think the Elite disc protection was based on 8271-specific tricks,
>which would explain the problems running it on the Master. In fact I
>doubt there have been Beeb game disc protections that did not assume
>a 8271 was present in the machine.

Correct. It was a dual 80/40 format disc, it contained code in the first
track which worked out if the drive was 80 or 40 track, and double-stepped 80
track discs. The code was very 8271 dependent, it had to mess around with the
track register when double-stepping to convince the 8271 that it was really
at track 39 when it had stepped to track 78.

It also was very tight for memory, and overlayed areas reserved for the DFS
with code. I had to re-design the memory layout for my own hierarchical DFS
to make it able to run Elite. My own Elite-A re-work is a worse offender in
this respect; I squeezed out just about every single byte of OS and DFS
memory so that I could to fit it in.

a.