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ITS and Imlac


Some ITS machines had Imlac PDS-1 machines attached. Primarily the Dynamic Modeling PDP-10, were the MAZE game was developed into a fast paced multiuser game. The Mathlab PDP-10 also had a few Imlacs, probably used mostly for Macsyma. As far as we can see, there also was one PDS-4.

Software types

The DM Imlacs ran older software called SSV, or screen saver. MAZE probably assumes some particular versions of SSV, which we may not have now. The preferred text editor with SSV is IMEDIT. The ITS terminal type for SSV is %TVIML, or OIMLAC in TCTYP. There is a newer software called SST which is much better for full screen editors like TECO or EMACS. This terminal type is %TNSFW, but it really is safe for work. The PDS-4 ran a tailored version of SSV called SSV4. There was also an ancient program called SIC, and a alternative program called WIMPY which didn't seem to gain a following. STV seems to be another name for SST.

Loading software

The Imlacs receive their software by upload from ITS. Start the Imlac bootstrap at location 40, and run the program IMLOAD. At the @ prompt, type OUTPUT_INPUT, where OUTPUT is Tnn: to specify the terminal line, and INPUT is the file to load. As a convenience it's possible to type just nn to load the “normal” program. IMLOAD tries to open, in this order, <user>; .PRGM. Tnn, <user> .PRGM. NORMAL, IMLAC; .PRGM. Tnn, and IMLAC; .PRGM. NORMAL. To reload the Imlac you're currently using, just type enter.

Development tools

Software development tools for the Imlac consists of the regular MIDAS assembler, a set of MIDAS definitions and macros to generate Imlac code, and the program IMTRAN which translates MIDAS binary output to a format accepted by the Imlac TTY bootstrap.


Josh Dersch has written an Imlac PDS-1 emulator, which can attach to a PDP-10 emulator serial line. ITS as built from the GitHub repository has T50 configured with the “OIMLAC” terminal type, i.e. Imlac running SSV. The PDP-10 emulator has TCP port 10016 connected to T50. The Imlac emulator can be conveniently started and connected to ITS by typing ./start imlac. When first started the Imlac memory is blank, so it must be loaded with IMLOAD.

Terminal types

The TCTYP program used to have a terminal type called IMLAC for Imlacs running SSV. When SSV fell out of favor, the IMLAC terminal type was changed to refer to SST instead. The old SSV type has been added back under the name OIMLAC. If the terminal type is wrong, output will look garbled; just run TCTYP to set the correct type.

Graphics files

SSV can display ARDS graphics. To view files in the -PICS- directory, run the IMPRINT program and pass a file name on the command line.

its_imlac.txt · Last modified: 2020/04/28 13:12 by lars