Apur-ee.294
net.unix-wizards
utzoo!decvax!pur-ee!ghg
Fri Apr 16 08:30:19 1982
\"Zork EMT trap\"
In 1978 a RT-11 floppy showed up here with Dungeon (zork) on it.
Having no source, I loaded and started it up on a PDP-11/45, letting
it run until the first prompt. The machine was halted, the registers
noted, and the entire core image copied onto a UNIX machine. About
two days later, after much adb and assembler, there was working UNIX
a.out for zork.  The UNIX startup prints out "there is a mailbox here..",
loads the core image, restores the registers to those from the 11/45,
and jumps back in.  The patched in assembler routines include the tty
I/O and an RT-11 overlay loader, and the ">" to save a game and a
"<" to restore a game. I could not even begin to figure out how
RT-11 fortran I/O (for savegame) worked; it looked at all kinds of
funny locations in the RT-11 monitor. If any of the fortran I/O
commands are used it will bomb zork.

I passed this out to Bell, and USENIX distribution tapes. Rumor has it
that some of the PDP-11 compat packages were developed for Vaxen
to allow zork to be played.  Also, zork overlays like crazy. It some-
times loads 8 or 10 overlays per command. So you get a big win if you
can put the "doverlay" file on a fast disk or use a large buffer
pool. This can be changed in the startup file "zork.c".
--Geo. Goble   pur-ee!ghg