Graham Irwin: computing reminiscences

Some of the more unusual computers I have worked on:

Elliott 803

Hatfield Polytechnic had two Elliott 803s to which some local schools and colleges had access. Mid Herts College of Further Education in Welwyn Garden City was one of those having remote access using a teletype and an acoustic coupler over a dial-up line which ran at (presumably) 75 x 1200 baud. The 803 had a rather unusual architecture with a 39 bit word comprising two 19 bit bytes and a modifier bit between. The computer would “sing” as it executed each instruction and there were several examples of early computer-generated music which made use of this feature. One of the lecturers at Hatfield wrote a compiler using a BBC assembler code which allowed three simultaneous users to access the 803 – quite an achievement for those days. The main input device was a 5-hole paper tape reader, and later 8-hole paper tape. Off-line storage was on sprocket-driven magnetic film. There are now thousands of web pages devoted to the 803 including a couple of video presentations: presentation 1, presentation 2.

Burroughs TC500

The ubiquitous TC500 seems to have found its way into almost every branch of every UK bank in the seventies. It was an odd machine with no core memory, and programs were executed directly off the disk. The machine code was even stranger with part of the instruction code indicating where on the disk the next instruction was to be found; thus it was common practice to create a loop without the use of a jump instruction. The TC500 was used by Burroughs as the basis for its foray into the design and development of cash dispensers, the RT (remote teller) series, initially for Midland Bank but later for export, particularly to the States and Europe. They were the first “holes in the wall” to use returnable magnetically encoded cards – at least in the UK. Barclays and Lloyds used paper vouchers like cheques with punched holes in which were retained after use, and NatWest used plastic cards that were retained and returned to the customer in the post! So concerned for security and the possibility of fraud was Midland that the RT1100 used a proprietary “secure card property” (SCP) which made each card unique and made it virtually impossible to duplicate a card. Unfortunately, it was so secure that it was also almost impossible to read the SCP consistently and the card was often retained without even giving the customer their £10 cash. I was recently reminded of the “dimple routine” which made a small dimple in the card to indicate how many times the card had been used. The card was retained after 20 uses and a new card issued.

Raytheon 704 and RDS 500

There’s a photo at: http://computermuseum.informatik.uni-stuttgart.de/dev/ray704/ray704.html. Very good machines they were, too, although not the most popular computer and even today the company is virtually unheard-of in many circles (not that it makes computers any longer as far as I’m aware). Equipped with a Floating Point Systems (FPS) array processor and CalComp pen plotters these machines were well suited to the processing of geophysical and seismic data.

Pegasus

I was just too late at City University to use the Ferranti Pegasus. It was being dismantled when I arrived and had been replaced by an ICT 1900.

Analogue/Hybrid

I think it was an EAI 640/680 (one of those meaningless TLAs) digital/analogue hybrid computer that I used at City University. In the days when everything seems to be going digital it must be hard for some to realise that there were even analogue computers at one time. My final year project was a macro-assembler for the 640 (the digital part).

And not forgetting the IBM S/360 and 1130; ICL 1900; Digital (DEC) PDP 8 and 11, and no doubt others will come to mind later...