Sunday brain tickler

[allison]

On 01/08/2017 09:09 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
>
>
I haven't ground on what it may be but there are four likely
directory/catalog cases.

Bag and tag, the file name starting block (or group of blocks) and
number of blocks.
usually byte pairs or longer ((16, 24, or 32bits) to get enough
addressing and large
enough byte counts.

CP/M like with entries for file name then a short list of allocation
blocks, additional entries
if the file is larger and needs for allocation blocks.  FYI CPM it can
be byte pairs or
single byte allocation list.

unix like with a simple filename and pointer to Inode there the metadata
and block list is.

Last case is a reserved set of blocks that are allocated as a linked
list and the directory
block has the filename and point to the start of the list.  Like unix
that can easily support
subdirectories.

None of those are processor specific but the cpu used often determines
things like if
there is bit packing.

As to radix, anything is possible also simeple things like high bit of a
8bit byte suggests
a control code or extended characters (or several things).

Allison