http://www.riscos.com/support/developer ... ecore.html has everything you would need (I think) to work out the necessary offset. There is a "Non-ADFS partition descriptor" in the boot block at &1FC - &1FE from offset &C00 on disk, which describes the start cylinder (&1FD=lobyte, &1FE=hibyte). The disc address of the RISC iX partition is then (start cylinder * heads on drive * sectors per track * bytes per sector). These values can be obtained from the Disc Record at offset &1C0 - &1FB from offset &C00 on disk. Getting the heads right might be little tricky because you would need to know whether the drive is interleaved or sequenced but if one doesn't look right, try the other.davidb wrote:Nice work! It looks like there are at least two partitions on that disk. I wonder if there's a tool available to extract them to separate images.
If it helps any, the GNU "file" tool is pretty good at identifying RISC iX floppy images so it would probably work on partition images once you dike them out to a file with dd and the correct offset. Here's what file said about my RISC iX kernel floppy image:
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kernel_disk.img: Unix Fast File system [v1] (little-endian), last mounted on /mnt, last written at Tue Nov 9 07:37:21 1993, clean flag 0, number of blocks 800, number of data blocks 703, number of cylinder groups 5, block size 4096, fragment size 1024, minimum percentage of free blocks 0, rotational delay 4ms, disk rotational speed 1rps, SPACE optimization