Date   : Mon, 13 Sep 1999 22:56:43 +0100
From   : Stuart William McConnachie <stuart@...>
Subject: Re: The full emulator

In message <19990913163716.9802.rocketmail@...>, FARAZ
CHOUDHRY <razzledazzler2@...> writes
>Tell me, what am I supposed to do
>with BBC files downloaded off the Internet using a PC then?
For BBC files in the Standard Archive Format (These contain a load of
files and associated .INF attribute files) use BBC Explorer to combine
them into a disk image.  BBC Explorer is available free from:
http://www.nvg.ntnu.no/bbc/util/BBCExplorer-2.zip

Of course there's also my DISKMGR program, which comes with the
registered version of pcBBC.

>  I'm
>confused now  -  how many conversion processes are needed to get the
>file read into the emulator,
1 to get into the pcBBC emulator (use BBC explorer for example).

> and then read also into the real thing? 
I presume you mean a real BBC.  If you want to transfer files in
Standard Archive Format you use BBCXFER, while disk image files can be
transferred using my PCXFER program (also with the registered version of
pcBBC).

>OK, I see I need to serial link it into a real thing.  
Yes.  IMHO the "best" way to transfer files is use the serial link to
get stuff either to or from a BBC onto a PC.  (By "Best" here I mean the
way that's going to work whatever PC FDC you have, not of course perhaps
the most convenient or quickest).

>Basically what's
>being said here that the DOS-sed BBC files have none of the load/exec
>address info required for the emulator, 
Yes, basically this is what is stuck in that extra ".INF" file which
comes with every BBC file in Standard Archive Format.  There's also some
fairly major file name compatibility problems between DOS and DFS.  BBC
file names a 1.7 format (if you include the DFS "directory" letter), DOS
files 8.3 format.  Certain characters are also illegal in file names,
but the illegal characters are different between DFS and DOS.  In short
attempting to represent DFS disks (which is the native format for BBC
disks, and hence supported by pcBBC) in a consistent and coherent way
within DOS is virtually impossible.

>or the emulator doesn't look
>for such information because it's being run on a PC.  
An emulator can either:
1) use a DFS ROM and emulate the disk interface at a hardware level.
This gives maximum compatibility with a BBC (which is what pcBBC is all
about), but requires use of a disk image.
or:
2) access PC files (using standard archive format to store the
attributes) and bypass the DFS completely.  Unfortunately this usually
results in subtle elements of the DFS being omitted and resulting poor
emulation, but of course it does give you the ability to read PC files
directly (although naturally you are unable to access disk images).

This is a fundamental design decision you make when you start out
writing your emulator - Am I going for PC file system compatibility or
BBC accuracy?

I prefer disk images, and not only because they offer maximum BBC
compatibility.  There's also the question of space on your hard drive
(an explanation of cluster sizes and one large file versus numerous
small ones is beyond the scope of this document).  Besides a disk image
is also a convenient way of archiving all the required files for a
single game or application.

>C'mon, a modern
>PC has megabytes of RAM to allow for as much as poultry 512K memory
>mapping, and what happens to the BBC file when put onto a PC?  
Usually, it loses it's file attributes (load and exec addresses).  We
have to construct a special way to store these, either as in standard
archive format or by using a disk image to represent the BBC file
system.  Sometimes it is also necessary to change the name of the file
when ported to the PC platform.

>Then I'm
>told BBC disks are too low density to be read into the modern PCBBC? 
>No.....
The floppy disk controllers built into most modern PC's are designed to
read 1.44Mb disks.  This is the standard modern PC format for floppy
disks.  BBC's, as you may recall, used 400K and 640K formats (DFS and
ADFS 80T DS respectively).  It is therefore the PC that can not read the
disks, not pcBBC or your floppy disk drive.

>Surely such incompatibilities shouldn't exist if PCBBC is supposed to
>be the ultimate BBC emulator for the PC,
I agree.  Perhaps we should get Bill Gates to support the DFS file
system under the next release of Windows then?  Wouldn't it be great if
files under Windows had proper assignable attributes and types rather
than using extensions to type everything (and then by default explorer
doesn't show you what they are, so you end up calling your files new
file.txt.txt - crazy!),

Regards,
-- 
Stuart McConnachie (stuart@...              )
43 The Hollows, Long Eaton, Nottingham, NG10 2ES, UK
Mobile: 0966 224307