Date   : Tue, 10 May 2005 09:44:35 +0100
From   : Richard Gellman <splodge@...>
Subject: Re: Beeb versus Master?

The only "it don't work on a Master" issues are that of undocumented 
opcodes, and the character definition space.

The former is only really a problem for games that use undocumented 
opcodes for performance reasons. Most control software do things 
properly, so Master-ability is not a problem. Also to note is that, the 
opcode issue died out around 1988/89 after all the software companies 
realised their stuff didn't work on the M128, and recoded it to work 
correctly. Thus, most games do actually work fine on ye olde M128.

The second issue is one of laziness on the part of the software author. 
VDU 23 (OSWRCH 23 in assembly terms) is used to redefine the appearance 
of characters in modes 0-6. In the Model B, these are held in "Low" 
(below &8000) RAM, in a specific location. They also require the use of 
a *FX (OSBYTE) sequence to access some of them. In the Master 128, they 
are held in High RAM, in a private address space. Now to the VDU 23 
user, there is no difference in use, but...

... Some dodgy software manufacturers (and I've seen educational control 
software do this, albeit for its title screen only) just make the 
appropriate *FX call, load a block into memory, and get on with things, 
assuming MOS will just use the data its given, with no thought for 
checking OS version.

The net effect of this is that some things look like they're written in 
quasi-arabic, rather than a full-out crash (as with the undoc'd opcodes).

To summarise: The Master 128 is technically superior, and 98% of the 
time it will run BBC B stuff without problems. But the occasional piece 
of software written by lazy monkeys might have odd behaviour.

I personally would never give up my lovely M128 (with 65C102 Internal 
Second processor, *cough*, Tube Elite anyone?).

-- Richard

P.S. Has anyone else been receiving spam via this list? Given that posts 
are supposed to require your sending email address matches that which 
you subscribed with, I find it interesting that spam is making it through...

neil f wrote:

>I have the choice of standardising on a Master 128 or building a heavily
>upgraded B. (It needs to be M OR B as I don't want too much extra
>hardware hanging around - I'm tripping over stuff all day as it is.) My
>main interest is in interfacing (science projects, robotics etc) with
>just the odd game played for old time's sake. Leaving aside the smaller
>footprint and much more attractive case of the B, are there any other
>advantages to it that I'd be missing? I'm assuming the Master is
>electrically similar or superior to the B, but are there software issues
>that make certain programs unavailable on the Master for instance. Any
>other issues I should consider. I have most of what I would need to go
>down either route, so cost is not an issue at this stage.
>
>Cheers,
>-Neil F.
>
>  
>