>From: Megan <mbg@world.std.com>

>>Sounds very much like OS/8 here. But if you have a bootable system, the
>>first directory block is at 60 instead of 7. (Might remember the block
>>numbers wrong, however...)
>
>That may be for OS/8, but 6/7 is most definitely the first segment for
>RT-11.  Boot block is zero, with secondary boot in 2-5.  Home block is
>block 1, with info about the rest of the disk.  Directory in 6/7 at
>a minimum... data blocks starting no later than 68.

The difference is that the system image does not appear as regular data
file(s) in OS/8, it's always in uncharted territory between the end of the
directory and the beginning of the data blocks.  The OS/8 directory is always
in blocks 1-6 (and unlike RT, the max # of segments is fixed), however the
first data block addressable by the directory can be either 7 or 70 (octal)
depending on whether it's a bootable disk.  Or theoretically any other value
but those are the two that are usually used.  Actually, on RT you *could*
tweak the segment headers to start the data somewhere other than immediately
after the directory, but, WHY!  The fixed-location boot stuff fits into a
pretty small piece of real estate and it's smart enough to find the files out
in the regular "data" part of the disk, so unless someone is doing something
nasty like writing RT-11 viruses (please don't!!!), why bother.

John Wilson
D Bit