Hello, Some of DEC's disks allow reading and writing the sector headers. ITS' disk formatting program, SALV (the Salvager), uses this to make a new file structure on a pack, and to verify its integrity.
This isn't fully supported by SIMH. The file PDP10/pdp10_rp.c has the comment "23-Aug-01 RMS Added read/write header stubs for ITS", and the stub is in "case FNC_WRITEH" in rp_svc. It's a no-op that just sets the DONE flag. What is supposed to happen is that SALV wants to write two header words with geometry information and then the sector data with a particular bit pattern. The verification phase reads back and checks the bit pattern. Since those bits aren't written, the verification fails. This isn't so bad since SALV offers to skip the verification. But now this has come up again using Rich Cornwell's upcoming KA10 addition to SIMH. The KA10 version of SALV does the same with an RP04 disk, but does not have the option to skip the verification. SALV also writes some information to the key fields in the headers, which is later read back. I'm wondering what your opinions are reagarding this? I see some options: 1. Do not change SIMH. Patch SALV to skip the verification. Obviously this is quite quick and painless, but leaves me with a slightly dissatisfied feeling. Some historical software isn't running properly. 2. Add header words to the disk image file. An incompatible change, but should of course be optional. 3. Store header words out of band somehow. Last in the image file? In another file? I understand the case for making changes to SIMH is quite weak if running SALV is the one and only use case. Are there any other programs that reads or writes the headers? _______________________________________________ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh
