Date   : Sun, 19 Feb 2006 15:17:21 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: Watford / Acorn DFS question

Jonathan Graham Harston wrote:
>> Message-ID: <43F0714D.2060904@...>
>  
> Jules Richardson <julesrichardsonuk@...> wrote:
>>> Unless I've misunderstood your question, Watford disks have two
>>> catalogues if formatted with 62 files - otherwise they look just like
>>> Acorn discs.
>> Ahhh, OK - so:
>>
>> If it's got a second catalogue it's a Watford disk and also supports longer
>> files (by optionally setting the high bit in byte 5 of the filename).
>  
> No. If it's got a second catalogue, it's a Watford 62-file disk.
> Full stop. Nothing else. Absolutely *NOTHING* implied about the
> support or otherwise of longer files.

Brilliant - ta :-)

 > DFS clears b7 of any filename when writing to the catalogue.

Although as your website says (and one of the DFS books I have here), early 
DFSes don't guarantee this :(

Seems like the first step in detecting a DFS filesystem is to sanity-check the 
disk geometry, then the file count field.

Then get the DFS type bits, followed by verifying DFS' idea of the total 
sector count.

Then sanity-check file offsets + lengths and make sure the catalogue is 
ordered (along with checking for a second Watford - or Torch - catalogue at 
this point)

At least that's the way I'm currently doing it...

cheers

Jules