Date   : Tue, 31 Jan 2006 11:57:18 -0000
From   : "David Harper" <dl.harper@...>
Subject: Re: BBC Master 512 system discs

Jules Richardson <julesrichardsonuk@...> wrote:

>> The 512's boot disk is a hybrid ADFS / DOS format disk. The 512's boot 
>> ROM uses ADFS to get started
>
> That's interesting - do you need ADFS present to even get the startup TUBE 
> message?

No, you don't.

If you just start up the 512 without booting (a "soft" Break), then you get 
into the 80186 Monitor. This uses standard BBC second-processor protocols 
(except that they don't all work, because of bugs!) You can use DFS disks, 
or whatever you want, from the monitor. No-one has written any useful 
programs (or any programs at all that I know of) which run in this 
environment, however. Hardly surprising, really!

After a "hard" Break, the initial messages come and the Monitor starts up, 
but instead of entering command-line mode it initialises ADFS. The monitor 
then uses the Beeb filing system to interpret the boot disk as an ADFS disk, 
and load into the second processor memory a program called "dosboot" which 
it then enters. This is sufficient for the 80186 to interpret the rest of 
the disk as DOS, and it can then boot up properly using the files 
DOSPLUS.SYS (the main DOS-Plus system), 6502.SYS (which is copied back into 
the host processor memory), LOGO.SYS (optional - just displays the DRI logo 
during the boot process) and COMMAND.COM (the standard DOS command-line 
processor).

ADFS can, in fact, be bypassed, but only by using other software. Essential 
Software's "Fastboot" program does this. It sits in SW-ROM and takes over on 
a hard Break (with the 512 active). It directly interprets the FAT on an 
Acorn-format 800K DOS disk, and loads in DOSPLUS.SYS and COMMAND.COM from 
that.

David Harper