🚀 go-pugleaf

Just before I started school there back in 1978, Tennessee Tech
University replaced its aging Xerox Sigma 7 computer with a brand new 
(but already-obsolete) Burroughs 6700. (Sigh)

Unlike the Xerox CP-V operating system which was full of holes, 
the Burroughs MCP (Master Control Program) was said to be very secure.
The new machine had no assembler or debugger with which to explore,
and Burroughs systems were popular in banks and other environments
where security was important.  So the computer center administration
was happy that it could relax a bit in the war against the students.

The "beast" (as we called it) had a large front panel facing the machine
room window so users could watch the lights blink.  The most noticable
feature on the front panel was a rectangular grid of 192 lights.
You could tell at a glance how heavily loaded the machine was, since 
the MCP's idle process would put a "B" (the Burroughs logo) in the 
lights whenever it was running. 


Imagine if you will a computer center director walking by the machine 
room a few months after the machine had been installed.  Casually he
looks through the window to see how the machine is doing, only to
realize that the front panel lights now form the pattern of a SIGMA.


As it turns out, all you had to do to accomplish this was to keep
the right bit patterns on the top of the stack (the B6700 was a stack
machine) -- this basically involved sitting in a tight loop doing a
bitwise compare of two double-precision values over and over.  So the 
system's security had not really been compromised (yet), but this was 
little comfort to one sysadmin who was convinced that the front panel 
lights were controlled by "the innermost part of the operating system"...

No, I can't claim credit for this hack -- but I knew the people who
worked on it and I did see the program run.  One of them eventually
went on to collaborate in the CMU "coke" effort after leaving TTU.

Keith Moore			Internet: mo...@cs.utk.edu
University of Tenn. CS Dept.	BITNET: moore@utkvx
107 Ayres Hall, UT Campus	UT Decnet: utkcs::moore
Knoxville Tennessee 37996-1301	Telephone: +1 615 974 0822