Jamtronix

I’ve been poking around some more in the film archive at MIT that I found “Making Electrons Count” and a few other items caught my attention.

First is a news report from 1951 showing the WHIRLWIND computer being used to solve some differential equations that would be very tedious to compute by hand (e.g. determining remaining fuel, height and velocity of a rocket as it is launched). Output to an oscilloscope and a flexowriter is shown, as well as some very early electronic music. 6 minutes long.

Then there is a talk from 1985 reflecting on 40 years of computing, covering the transition from computers being batch-mode number crunching machines, where any single programmer would be allowed a short window every few days in which they could attempt to run their program, into “time-sharing” data processing machines, in which multiple users could be constantly interacting with, allowing for (amongst other things) ‘on-line’ programming. It is hard to comprehend what the act of developing and debugging a program would be like when you would only be allowed 1 attempt to run it every 3 days.

This film is 90 minutes long, but the main speaker (who appears about 7 minutes in, after a somewhat boring introduction from the MC) is very engaging and uses photos and other props to entertain and inform.

The RPC-4000 (like many computers of the same vintage) used a device called a Friden Flexowriter for input and output. This device was a combination typewriter, printer and paper tape reader & writer.

Input to the RPC-4000 could be done either by typing on the keyboard, or reading a paper tape. Output from the RPC-4000 would be printed to the flexowriter.

The character set used by the RPC-4000 is essentially the Flexowriter character set. It uses 6-bit codes, allowing for 64 characters, as opposed the 128 characters in 7-bit ASCII. However the flexowriter had a typewriter  mechanism that allowed for shifting between upper and lower case, and there are codes in the character set that select which case to use for printing of subsequent characters.

The Flexowriter character set also has some ‘control codes’, similar to the control codes that make up the first 32 ASCII characters. Nowadays most of these control codes are long since obsolete, since they relate to long dead media like 80 column punch cards, paper tape or magnetic tape reels.

While looking for the definition of some of the Flexowriter control codes referenced in the RPC-4000 documentation, I stumbled across ‘Making Electrons Count‘ – a documentary made in the early 1950s about the MIT “Whirlwind” digital computer facility. It is 20 minutes long, the first 10 minutes or so are a breathless description of the wonders of digital computers and the bright future they would bring us.

The 2nd half I found eye-opening; it tells the story of someone with a complex maths problem to solve, and the journey they go on to program the Whirlwind to solve it, which includes digesting a thick tome on  “PROGRAMMING: Statement; Mathematical Analysis; Flow Diagram; Code; Tape Preparation; Computing; Debugging; Interpreting Results.”, attending a 2 week programming course, several interactions with Flexowriters, and a 4:00am visit to the “Night Typist”.

As well as the video itself, I also came across a nice commentary on it that gives a lot of useful context to the technology and techniques captured in the film.

These were zipped at The BBC Lives!

The BBC Micro Operating System ( a series that first published on Micronet between April and October 1991 )

Acorn MOS 1.2 Disassembly part 1 (VDU fonts & contstants : $C000 – $C4BF)
Acorn MOS 1.2 Disassembly part 2 (OSWRCH : $C4C0 – $CA38)
Acorn MOS 1.2 Disassembly part 3 (misc graphics routines : $CA39 – $D4BC)
Acorn MOS 1.2 Disassembly part 4 (D4BD – $DB10)
Acorn MOS 1.2 Disassembly part 5 ($DB11 -$DEFE – possibly incomplete file? )
Acorn MOS 1.2 Disassembly part 6 ($E114 – $E6AF)
Acorn MOS 1.2 Disassembly part 7 ($E6B0 – $EAD8)
Acorn MOS 1.2 Disassembly part 8 ($EAD9 – $F134)
Acorn MOS 1.2 Disassembly part 9 ($F135 – $F9B3)
Acorn MOS 1.2 Disassembly part 10 ($F9B4 – $FFFF)

I added some new decoders to peekbot

• DFS filesystem as used by 8-bit Acorn machines, e.g the “BBC Model B” my school used (sample)
• BBC BASIC (sample)
• “Micro Painter” picture format for 8-bit Atari (sample)

Also, the symbols table used by the disassembler has been extended to allow for decoding of functions that are all called via a single address (e.g. the BBC has a routine called OSBYTE which is accessed via $FFF4, but has hundreds of different sub-functions which can be selected via different values of A,X & Y registers). Only immediate loads in the vicinity of the JSR are interepreted (e.g. LDA #$01/ JSR $FFF4).