Date   : Thu, 29 Feb 1996 17:19:36 GMT
From   : lamcw <lamcw@...>
Subject: Re: Emulation systems

Tom Seddon wrote:

;My disk format consists of a single file which contains BBC files inside
;it, one after another


I read your reasons for this but I'm not too sure. My one (MacBeebEm)
just reads in files off the hard disk as and when they're needed, treating
the
hard drive as one great big virtual cassette tape. 

All disk images can be split into separate files with headers. MacBeebEm's
headers have the following 10-byte format...

  Offset        Value
     0          255
     1,2        lo, hi load address
     3,4        lo, hi exec   "
     5          checksum *
     6,7,8,9    spare and may take any value


Checksum is the sum of the 4 address bytes AND &FF. If the the 1st byte is
not 255 and the checksum does not match the addresses then MacBeebEm
will not load the file.

The last 4 bytes are for future expansion and maybe emulator specific.

Perhaps we can have some discussion and agree on a standard header.

I also have a *=dir command which give one level of subdirectory which
allows users to organise files. So put all your Elite files into a folder
called elite-dir and type 

  *=elite-dir
  CH."ELITE"


I prefer this cassette system because it's very simple and casts off the
shackles of having disk-image entities with horribly vague names like
"GAMES5". Imagine having dozens of these and wanting to find one particular
game.


Chris Lam,
MacBeebEm Keeper.