Version 2.1 of the Burroughs 220 Simulator has been released. Michael J. Mahon, the author of the B220SIM App announced it in a posting on the Comp.sys.Apple2 group on usenet
From Michael J. Mahon on the CSA2 Groups:
it’s been a few years since I released version 1.2, which completed the
simulation of the processor and rudimentary I/O of the Burroughs 220
computer. It correctly ran the machine diagnostics and had sufficient
I/O capability to run an assembler and numerous sample programs.
What it could not do is run the Burroughs Algebraic Compiler for the 220
(BALGOL), nor could it simulate the interactive graphics I/O devices
that extended the B220 installed at Caltech–a machine that I came to
love as my second “personal computer” (after the IBM 1620). Both early
machines took up a room-sized space, but I was able to use them
directly, sitting at their consoles, just as I would use my Apple ][+
seventeen years later!
I was pretty happy with the functionality of B220SIM v1.2, but I had
always hoped to be able to run BALGOL, an amazingly complete and fast
load-and-go compiler for Burroughs’ variant of Algol 58 that was first
shipped to customers in 1961. It was a beautiful creation of several
early giants of computer programing, a team led by Joel Erdwinn,
including Donald Knuth (who wrote a compiler for the same language for
the Burroughs 205).
BALGOL required a fairly complete implementation of the B220 mag-tape
subsystem, including the ability to search the tape for specific blocks
(pretty advanced for its time–more like a “linear disk” than the IBM
tape model).
One reason the version 1.2 tape implementation was so basic is that 64KB
was just about filled with just a simple implementation, and had no
buffering. So I started version 2 with the assumption of a 128KB Apple
//e or IIc and proceeded to learn about writing bank-switched code.
The v2.1 simulator itself is in AUX memory, and main memory is used for
the human interface, graphics buffer, I/O buffers, and the mapping of
B220 I/O devices to ProDOS disk files. In the process, I simulated the
DEC 340 CRT display that Caltech attached and the light pen and
specialized interactive keyboards that were stationed with the CRT display.
If any of this sounds interesting, take a look at B220SIM v2.1 azt my
website, where you can read more about the simulator and the B220,
download the simulator and its source (and some sample programs and
utilities), and take a look at the actual assembly code.
—
-michael
NadaNet 3.1 for Apple II parallel computing!
Home page: http://michaeljmahon.com
“The wastebasket is our most important design
tool–and it’s seriously underused.”
