Date   : Fri, 19 Nov 2010 21:21:11 +0000
From   : zeem.uk@... (Alex Taylor)
Subject: BBC file formats

On 19 November 2010 20:57, James McGill <plexer@...> wrote:

> I'm curious, what was the purpose of shifting the machine code in that
> BASIC loop, rather than loading it there directly, and what was the
> advantage of having moved it there?

I have vague recollections of doing this on my Electron when I bought
a brand new PRES AP3 and 3.5" drive, using money earned from
delivering free newspapers.

For an otherwise unexpanded Model B or Electron, PAGE is set to &E00
for a cassette-based machine, having a disk system pushes PAGE up for
the workspace it needs (&1D00 is ADFS if I remember correctly, DFS
sets PAGE to &1900).

I recall that loading something over the disk workspace would crash
the machine. The technique is to load everything in higher up in
memory, then when everything's loaded, to move it down in memory. At
that point nothing more can be loaded from disk without doing a
CTRL-BREAK.

-- 
Alex Taylor