The Jim Austin Computer Collection

Elliott 903

The Elliott paper tape punch (left) and reader (right) Sitting on the machine, the control panel is on the far right.

Introduction

The Elliott 903 machine is a transistor based computer from the late 1960's. It is made up of a number of cards each with a few gates on. The machine came from  Hull University Psychology Department where it was operated until about 1975. The machine was removed because the room was needed. The system consists of a Main processor, Control panel, Paper tape punch and reader and a ASR 33 teletype for input and output.

The following is from the Computer Conservation web site where an emulator for the Elliott 903 can be found (http://www.cs.man.ac.uk/CCS/ccs_arc2.htm).

"The Elliott 903 was manufactured by Elliott Automation Limited from 1965 as a desk-sized successor to the military computers 920B (in Nimrod Mark I) and 920M (in RAF Jaguars and in tanks). It had an 18-bit word ferrite core store with a 6 microsecond cycle time, paper tape I/O and a Teletype. Up to 64K words of store could be fitted in units of 8K. The 905 was a later faster machine which could have 128K words of store.

The machine used transistors on plug-in packages. Peripherals could include a plotter, a line printer, magnetic tapes, industrial interfaces, and displays for plant monitoring. There was no disk to act as a focus for an operating system, although one based on magnetic tape was written and several for real-time applications.

Counting the military versions probably about 1000 machines were sold. The 903 itself was used in process control, for running laboratory equipment in hospitals and elsewhere, and for teaching programming in schools. Languages available included Algol, Basic, Coral, Fortran and the SIR assembler."

Recollections of Elliott 903 machines

"This was the first machine I used whilst at school (Eton
College, England). We used it to process exam results as
well as learn about computers. One fun thing was to get it
to play tunes (it had a beep). You could get a second note
for harmonies from the paper tape reader electromagnetic
clamp. Provided you switched it on and off fast enough, it
could play bass notes. However it wore the clamp out rather
quickly. I remember the service engineer commenting that
our machine blew more tape clamps than all the others he
serviced put together. I wonder why! Eventually the school
replaced the Elliott with a pack of TRS80 micros. They cost
less than one year's service contract on the Elliott. We
used to run Fortran and a made up language called 'Sympol'
(or Symbol?) on the Elliott. Another trick we performed was
to change the Sympol compiler tape with one where we had
changed the interpretation of + for - and * for /. 
Therefore all the other students' program gave incorrect
results. Happy days.

Another thing I remember about the Elliott was that most of
my programs were reset-jumped at 8181 - I'm not even sure
what that means now, and I never knew why! You had to set
the number up on the toggles on the control panel that you
have in one of your pictures. We also had a terminal that
was connected directly to the computer, so it was possible
to interact quite well with it - however I think the Elliott
acted as if it was connected to a teletype, so that the
screen updated at about 5 cps."

Richard Gibbons, January 2005

 

The following recollections are from Richard Blackett (June 2007)

 

I worked on the RAF Elliott 920B's at RAF Wattisham in the early 80's. They were used on the Nimrod it's true. As the last person trained to service to component level I fixed the air borne version but ours were originally used to control air defense systems putting track markers up for RADAR and controlling Bloodhound ground to air missiles. The 920B was particularly resistant to electro magnetic interference. Ours would sit happily through RADAR side lobes that would reset every other computer on the base. They were replaced by the 920C but were used for programme development in a language called MNAP. I was particularly impressed as they made a different "squeek" according to what process they were doing. It meant you could run a test loop programme and sing along. You would always know when it failed as it would go off pitch. Ours could be programmed to play the flight of the bumble bee and air on a G string. Incredibly impressive at the time and must of taken someone hours to do. We also had a programme called visiprint which punched holes in paper tape as readable letters. Great for Just Married etc.%0D%0AGreat to see the pictures. I've been up to my arm pits in those boards soooo many times.

 

It was nice to see them (903) still is existence.

The 920 was identical as far as I can see. the controller was the 903 unit as you've got in the picture. Note the screening around the cover of the processor to block external interference.

The "Network" was connected with 212 way cables about 4" in diameter and had an enormous communications rack to connect to the Bloodhounds by dedicated phone line.

The technology was a mixture of DTL and TTL. The modules made very cute key fobs. If yours doesn't work I recommend popping the cover off the core store to have a look at the ferrites. I would also, for display, take the cover off the paper tape reperforator (punch) to show the working parts. I used to teach servicing on those. If you were good you could set it so when you ran your hand down the tape you couldn't feel the holes at all.

I think ours were removed to storage in about 1983 or 84. The store in Wales had hundreds on boxes with this stuff in them. The mobile version we had sat on specialist pallets. You just dropped four sides and a top on them and fork lifted the box into an aircraft for deployment. I never saw that.

 

we also had a desk top board fault analysis machine. I can't remember what it was called. When I arrived at RAF Wattisham in 1980 it didn't work because (ironically) the only way to test its boards was on it. I spent 2 years, on and off, fixing it but it was very efficient at isolating, to the module, faults on the 920 cards.

 

Oh, and finally, because even I can see I'm getting boring, the other user who remember it mentions an 8181 to start. This was because an 8 command was an unconditional jump and 181 was just an arbitrary start point. commands 4 and 5 were addition and subtraction and 15 was the input/output set. 15 commands -  true RISC. I didn't programme it enough to remember more. I suspect 8181 is just an easy shape to key in. Ours always started at 8 so I think 88 was our start point. This could be untrue....my memory is weak on these things.

Recollections from Terry Froggatt, April 2008

I worked at "Elliotts" on the 900 series, at Borehamwood then Rochester, from 1966 to 1976.

Regarding the postings on your web site, Richard Gibbons remembers resetting and jumping to 8181, but cannot remember why. 8181 was simply the address of the entry point of the hard-wired initial instructions, which I've written up on the Computer Heritage web site.

Richard Blackett's reply is not quite right. He suggests that the first 8 means jump (and that 181 was an arbitrary start point). It is true that you could obey "8 8181" on the hand keys to jump to initial instructions, but they will only work if you are on the top interrupt level. Pressing "jump" rather than "obey" ensures this. We would normally set the B and function keys up, and set all of the address keys down by running a hand across them (giving address 8191), then subtract 10 by making a V-sign gesture under the 8 & 2 keys.

Richard Blackett also says that function codes 4 and 5 were addition and subtraction. No, function codes 4 and 5 are "read memory to accumulator" and "write accumulator to memory". Addition is function 1, and subtraction is function 2. In fact, function 2 is actually a "backwards subtract" which negates the accumulator then adds the word from memory. This is more useful than subtract, because it can be used as "negate" (with an all-zero word in memory) and as "not" (with an all-ones word in memory).

This is a nice web site which lists all the 900 series machines http://www.ourcomputerheritage.org/wp/. The page lists 144 machines made. This one could be one of the Hull machines listed. I think it was delivered new to Hull University, so it may be one of the unnamed machines. This has now been confirmed (April 2008).

More pictures

Picture of the processor cards

Picture of the front panel