Is PACK on the HP-71 buggy?

[Joe Horn]

(07-15-2014 06:13 PM)rprosperi Wrote:  Probably the worst case scenario is packing a volume whose directory has only 1 or 2 open slots. The bogus entries might conceivably get written past the end of the directory table and into the file data area?

Turns out you're exactly right. The INDX89 swap disk (in the MoHPC ftp archive) has 0 free directory entries, which means its file contents begin immediately after the end of the directory. Performing a PACKDIR on INDX89 destroys the contents of the first file on the disk, namely NOTICE71 (a notice from Mark Cracknell, 1 March 1989, forbidding commercial use of the disk) by overwriting its first 256 bytes with garbage. If the file is then copied into an HP-71, attempting to print it can cause a crash.

Furthermore, if PACK is used (instead of PACKDIR) on INDX89, the PACK operation bombs out before finishing, possibly resulting in loss of the entire disk's contents.

Bottom line: Don't use the HP-71's PACK or PACKDIR unless (a) you can see with a hex editor that there is at least one entire free record (256 bytes) between the last directory entry and the beginning of the contents of the first file, and (b) you will NEVER afterwards add anything to the medium using the HP-41 HP-IL module. Otherwise data loss will occur.