Sunday brain tickler

[jim stephens]

I don't know the names, but the use of extents might be something going on.

I highlighted the c4a3 extent.  The last two columns maybe cylinder and 
sector number.

There may be a free count going on with the next to the last two bytes 
0xff85 for instance in the first stick.

Since line 0x000 is odd, i wonder if it is volume related or other with 
the application of the disk.  I'd guess that line 0x0007
is also possibly volume related.

The only deviating entry at 073 has a 7f in what I'm guessing is the 
cylinder column, so maybe an "erased" entry?

And for whatever reason, there are 6 bytes "live" in the beginning, the 
two bytes of 0x0000 in all the entries as well.

As to the missing file names, I wonder if that data is in the text of 
the disk.  That was one way that file
systems had to pay with variable length packed data since tables like 
this was necessary with fixed length.

I am guessing you don't want to share the file names, but I'd take the 
numbers in the cylinder and sector columns
and see if you can spot something like filenames and the like.

I had a file system on a Microdata 1621 based mini that i wrote, and we 
put the directory entry in both the main
VTOC and in the heading of the first sector of the file.  Thank god for 
that, as one time we had a malfunction and
had to do a VTOC rebuild from scanning the entire disk, but that's 
another story.

Thanks
Jim

On 1/8/2017 6:09 PM, Chuck Guzis wrote:
> On 01/08/2017 04:42 PM, william degnan wrote:
>> Inverse 8085?
> I don't think so.  If it helps, here's the first few lines of the
> "directory":
>
> 000:  00 a1 7a c1 c0 00 00
> 0007:  00 00 00 00 00 00 00 80 1a 02 38 00
> 0013:  a1 7a c1 c0 00 00 00 00 1b ff 00 00
> 001f:  5c 25 15 1b 4c 40 00 00 ff ff 37 05
> 002b:  94 2f 38 40 00 00 00 00 ff 8f 31 01
> 0037:*c4 a3 75 6a ab 52 00 00 ff 85 25 05*
> 0043:  94 2f 38 40 00 00 00 00 ff 02 0f 02
> 004f:*c4 a3 75 6a ab 52 00 00 ff b6 09 04*
> 005b:  94 2f 38 40 00 00 00 00 ff 03 02 03
> 0067:*c4 a3 75 6a ab 52 00 00 ff 01 12 01*
> 0073:  d0 7f 9f 12 1f bd 53 28 ff ff 7f 02
> 007f:*c4 a3 75 6a ab 52 00 00 ff 01 2b 00*
> 008b:*c4 a3 75 6a ab 52 00 00 ff 83 28 04*
> 0097:*c4 a3 75 6a ab 52 00 00 ff 01 38 00*
> 00a3:  94 2f 3e 80 00 00 00 00 ff 01 1d 00
> 00af:  94 2f 4b 00 00 00 00 00 ff 03 35 05
> 00bb:  94 2f 4b 00 00 00 00 00 ff ff 3e 06
> ...
>
> There are no other tables on disk. The disk itself is hard-sectored,
> with a sector length of 150 bytes and 16 sectors per track.  They're
> interleaved 3:1 and grouped into blocks of 1200 bytes.  The directory
> would correspond to block 0 and there are 72 entries in it, less the header.
>
> I can get the raw text, but how it's linked together and what file names
> might is still a mystery.
>
> --Chuck
>
>
>