Leo III Intercode resurrection
The main systems programming language on Leo III was Intercode.
Most applicatons software was written in a COBOL-like language called CLEO.
Unfortunately a surviving CLEO compiler has so far eluded quite thorough searches.
We have three surviving Intercode systems programs, and one simple program listing
All four are from the days of the operational real machine.
Summary of emulation facilities
There is an
which allows you to type in an Intercode program, then translate and run it.
There are also facilities for running an emulated Leo III on your own computer.
The most realistic of our demonstrations is:
This gives quite a realistic demonstration of operating a Leo III, and also shows fairly
convincing Leo III characters on the printer.
All is revealed in the readme.htm file in the ZIP file, which is also
It is somewhat harder to drive than LeoIIIdemo2 as it requires some Leo III operator skills,
which are explained in the readme.htm file, but it gives much more of a feel of a real Leo III,
than our other demonstrations.
There are two other demonstrations showing the rescued Leo III software in action.
Unlike the above demonstartion, you do not get to interact much with the “machine”,
but you see a realistic sessin of Intercode transtations and execution, including the generation
of a new Master Routine.
The neatest one is at:
This does contain 2 tape images which are binary files which just might upset some anti-malware software.
An earlier version of this demonstration generates everything from plain text files and is at:
Each ZIP file contains a readme.htm.
The emulation software is written in C, and the source text is in each of the sets of files.
A Windows binary is available via a link in the readme file.
The demonstrations have been run successfully on various types of system, including:
Intel Pentium: Windows 98SE, Windows 10, FreeBSD, GNU/Linux (ubuntu)
ARM: GNU/Linux (Raspberry Pi)
Mac: OSX on MacBook Pro
SPARC: Solaris (using both gcc and cc compilers)
There is also a package intended to give a nostalgic experience to ex-Intercode programmers.
It has been produced by two ex-LeoIII programmers, Ray Smith and Ken Kemp, and
can be seen