Joseph.Ginder@CMU-CS-SPICE (04/21/83)
>From -- John Strait of 3RCC through jrg@cmu-cs-spice
--start forwarded message--
Re: PERQ RT-11 floppies ala Gene Spafford
From: J Strait at 3RCC
Gene described a problem using the PERQ Floppy utility and the 4.lbsd
Unix program arff. As I understand it, he could create floppies with
arff and read them with Floppy but not the other way around. Even
worse, once he used arff to write a floppy created on a PERQ, the
floppy got messed up so badly that he could not read it on a PERQ.
I know of two things that might be resposible for this problem.
1. The RT-11 directory format allows one to switch select larger than
standard directory entries when creating a directory. The extra
words in the directory entry are ignored by RT-11. The PERQ
floppy utility creates such directories and uses the extra space
to store "bits in last block" in order to keep track of file lengths
which are not block multiples.
We know from experience that standard versions of RT-11, RSX-11M, and
VMS have no problem with floppies that have extra word in the
directory entries. It is possible that arff, not being a standard DEC
program, cannot deal with directory entries that have extra words.
On the other hand, arff may actually want directory entries that
are larger than standard, but uses the extra words for something
different.
2. RT-11 floppies store files contiguously starting immediately after
the directory. In order to cope with floppies which have more
files than fit in the limited directory space, the format allows
new directory sections to be added in the middle of the floppy
(in a previously empty section) and linked into the existing
directory structure. Thus, unlike data files, the directory
need not be contiguous.
As near as I can tell, the PERQ floppy utility can read such non-
contiguous directories but cannot write them. It is possible that
arff treats this differently than the PERQ.
The PERQ initializes RT-11 floppies to have 4 "segments" with
1 extra 16-bit word per entry. This leaves room for 63 entries
per segment or a total of 252 files.
My best suggestion is that Gene try using arff to create the initial
directory making sure that it has enough room for the files. If this
fails to clear up the problem, it is likely that arff and Floppy are
non-standard in mutually exclusive ways. Good luck.
--end message--
P.S. Reply to jrg@cmu-cs-spice, I'll forward messages to John.