Torch Z80 Hard Disc Partition Information

[g7jjf]

I am adding Torch Z80 format discs to my ADFS.NET Explorer program. I have got floppy images working OK but I am struggling to process hard disc images (such as sasi0.dat which is part of the BeebEm distribution). I know this image is partitioned as 4 x 4MB drives and 1 x 3MB drive but I can't see anywhere within the disc image where this partition information is stored. It looks to be somewhere between offsets 0x1F00 to 0x1F7F but I can't decode the bytes within this sector to come up with the drive layout. Does anyone know how this information is stored as I can't find it in any documentation anywhere.

Thanks in advance.

[jgharston]

There's some information in the Torch documentation, but it is a bit fiddly to understand - and my copy is in storage at the mo. I'll dig it out and see if another re-read makes it any more comprehensible, particularly if there's an existing disk image to compare it with.

[g7jjf]

Thanks, that would be a great help

[BeebMaster]

I found a sasi.dat in a very old version of Beeb-Em (0.0.13) date stamped 14/10/2006, which is probably the last time I used an emulator, and also appears to be 940th anniversary of the Battle of Hastings, though that might not be relevant.

At &1F00 there looks to be some information which is similar to SASI/ST506 type mode sense information:

Code: Select all

0000:1F00 | 02 67 04 00 00 00 80 0B  02 13 00 0E 00 00 00 00                                                                                                                                                       | .g..............                                                

&267 would be 615 cylinders, 4 is the number of heads, not sure about all the rest, the 2 following pairs of 00 could be the RWCC and WPC cylinders, &80 could be landing zone offset, not sure about &B, 2 could be step rate code. Or &020B80 could possibly be the number of sectors, that would make it about 32MB on 256 bytes per sector.