Date   : Fri, 04 Jun 1993 09:40:26 BST
From   : ajcd@...
Subject: hdfs

From: I Stephenson <ian@...>
>
>In addition to the heirachical directory structure (not perfect but still  
>pretty cool), the big plus points are:

Yes, the hierarchical structure was dictated by wanting it to be
Acorn-compatible, which either required two different systems for reading and
writing catalogues, or to stick closely to the acorn directory structure. The
latter option won in the end. Another important consideration was that there
is no way of detecting when a disc is removed, so no vital information is kept
in memory when the disc is not being accessed. There are time and flexibility
overheads in doing it this way, but I'm quite pleased with the overall result.
Another point in the current directory structure's favour is that you can copy
directories around using the normal Acorn DFS, and they will still work if you
use the HDFS. (Each directory is completely self-contained, with no parent or
back pointers; the only piece of information particular to a directory in the
parent catalogue is the D bit.)

>       Loads of extra utilities that were previously in other roms like (say)
>Disc Doctor

Which are all tube and sideways-ROM transparent, which is a major win for me
(I run with a tube most of the time). Being able to auto-boot without the Tube
(CTRL-I-BREAK) is another advantage, because I don't have to turn the tube off
(putting nasty transients on the power lines) to play games.

There aren't any major bugs in it (I've been using this filing system
exculsively for the last 4-5 years and have probably had all the nasties
happen to me).

There are a couple of buglets which I've found recently (*fedit and *dump on
zero-length files give the error message "Bad Start", which is not
particularily helpful), but I don't really feel they're worth fixing yet.

The biggest point that I'm not pleased about is that the ROM is non-reentrant,
so text printed by the ROM itself cannot be *SPOOLed. To do this, the memory
areas used by OSGBPB, OSBGET and OSBPUT need to be completely seperate from
the areas used by the rest of the ROM, and this just wasn't possible with the
memory available. The manual contains all of the command descriptions anyway,
and the syntax is available as a reminder via *help.

I've an ongoing project which I've currently shelved in favour of re-writing
my assembler and disassembler ROM, to make the AMPLE ROM tube-compatible. I've
got a disassembly of it, and I think that it might be possible using events
driven by the interrupts from the 1Mhz bus, but I probably need more
information about the hardware. Has anyone got any technical specs of the
Music 5000 hardware which they can share?

a.
--
Angus Duggan, Department of Computer Science,  | Jobless, Phdless, clueless
University of Edinburgh, The King's Buildings,  | PHONE: +44(0)31 650 5126
Mayfield Road, Edinburgh EH9 3JZ, Scotland.    | INET: ajcd@...