Burroughs 220 Simulator Updated

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.” 

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