The Computer “CSIRAC” (1965)
Think you’re an early adopter? CSIRAC was an automatic digital computer, the fifth computer of its kind ever built. It weighed 7,000 kg and had a RAM of 768 words.
Although its function has been superseded by more modern machines, it has some unique features. In this film Trevor Pearcey, who designed the logic of the computer, discusses some of its features with Dr Frank Hirst of Melbourne University and outlines some of the problems that he and Maston Beard, who designed the electronics, had to overcome.
[Title appears: The Computer CSIRAC]
[Camera pans around the computer room to show Dr Frank Hirst and Dr Trevor Pearcey sitting at a computer]
Dr Frank Hirst: Trevor, how did it come that you designed the machine with 16 D Registers? [New text appears: Produced by the CSIRO Film Unit] Dr Trevor Pearcey: Well we first mastered the problems associated with a single register and then realised that we could put in 16 words into one adding unit thereby multiplying the capacity of the adder. [New text appears: Direction, Photography and Editing, Peter Bruce – Sound Recording, David Corke – Production, Stan Evans]
Dr Frank Hirst: Yes, it seems a pity really that more modern machines haven’t got quite so many D Registers or index registers as CSIRAC.
Dr Trevor Pearcey: Yes, this is so. Only recently when designers have been aiming at running more than one program at a time have the number of registers increased markedly.
Dr Frank Hirst: This is the computer CSIRAC. It was the first fully automatic electronic digital computer to be built in Australia. [New text appears: Dr. Frank Hirst, University of Melbourne]
It was constructed in the Radiophysics Division of the Commonwealth Scientific and Industrial Research Organisation to the designs of Mr Trevor Pearcey and Mr Maston Beard. Mr Pearcey was responsible for the logical design of the circuitry and Mr Beard engineered the electronic components.
This computer is of advanced electronic design for its day and it has a very flexible command code. We are fortunate to have Mr Pearcey with us now, its designer, and Trevor, perhaps you could relate to us some of the ideas that you had when you designed the machine.
[New text appears: Mr. Trevor Pearcey, CSIRO]
Dr Trevor Pearcey: The automatic digital computer which… CSIRAC was a very early example, was initially the product of the pooling of ideas by the mathematician and the electronic engineer who brought the ideas of the mathematician to physical realisation. Three basic principles are involved in the automatic digital computer. One, that the fast computer must be provided with a sufficient internal store so as to be able to hold its program that is the sequence of operations which it is instructed to perform. The second is that data and program are formally identical and are in fact held within the same store. The third is that program must consist of a network of sequences of instructions and that the computer traverse this network in a manner which is determined by the partial answers. In this way the computer is given the facility for discriminating between differing conditions, the conditions being those which it had already computed and to thereby repeat the program frequently but in slightly different form.
Soon after World War II the need arose in the Division of Radiophysics of what was then CSIR, for both a more rapid computing capability and for continued development of the electronic pulse techniques which had been developed for radar during World War II. Digital computing it was seen would serve both these purposes.
[Image changes to a tracking shot showing racks of electronics and valves within the metal cabinets of CSIRAC, then goes back to Dr Trevor Pearcey]
In 1948 the division undertook the study of automatic digital computing and in 1951 CSIRAC, this machine, was actually exhibited publicly in operating order and has since then been in regular service for the best part of a period of 13 years. During some of this time it has been improved and during the last nine years of its life has been used as a teaching and research machine in the University of Melbourne.
The design, although using engineering methods, which have now been rendered obsolete by the invention of the transistor, concentrated upon logical functions which would render it easy to use and some of them have been incorporated in machines to this day. [Image changes to a zoom into banks of electronic valves within CSIRAC then back to Dr Trevor Pearcey]
A set of 20 binary digits tells the machine how to move one particular datum from one part of the machine to another at the same time carrying out a simple operation upon it such as addition.
The program, which it performs, consists of a set of such simple transfers of data with appropriate transformations during their passage. The main store of CSIRAC and most of the incidental registers consists of a number of acoustic delay lines.
[Image changes to a man removing a long rod from a metal box then changes back to Dr Trevor Pearcey]
These take the form usually of pipes containing mercury, each one about five feet long down which acoustic waves travel taking a time of about one millisecond. When they reach the far end of the pipe they are detected, amplified and recirculated to the starting point. By this means CSIRAC was able to store 756 items of data, that is, six decimal digit items, or the equivalent, and to be able to operate upon them a thousand times a second. This is indeed slow compared with 500,000 operations a second, which are now on current machines.
[Image changes to a pair of hands holding up a wide paper tape with small holes punched through and then a narrower punched paper tape] Its main medium for accepting programs and data is paper tape of two kinds, one a wide kind with 12 channels frequently used for recording programs and one of five channels identical with paper tape used in common telegraphic equipment.
[Image changes to keys on a typewriter then back to Dr Trevor Pearcey]
Program and data are coded automatically by special devices with typewriter type of keyboard and the machine can read these tapes at about 100 rows per second or twenty 5 decimal digit numbers. Output onto similar tape is slower at about six 5 decimal digit numbers over the equivalent and these are printed out after punching at a later stage on similar keyboard instruments.
[Image changes to a large electric motor then back to Dr Trevor Pearcey] CSIRAC has now been rendered obsolete by recent developments in electronics and problems have grown too large to be held within it and too time-consuming to run. Problems are common now which can only be performed on equipment of vastly greater size and speed, computing and storage capacities being at least 500 times that of CSIRAC with correspondingly fast input and output devices. These are all now currently available and are being installed throughout Australia.
Here you see a program being recorded on wide paper tape.
[Image changes to a lady typing on a keyboard then pans over to show holes being punched into a paper tape]
An instruction written by the programmer in a fairly simple computer language on his sheets of paper is transcribed through the keyboard and you will notice that two keys are depressed before a punching action takes place. An instruction then consists of two groups of ten binary digits.
[Image shows the typist picking up the paper ribbon and giving it to Dr Trevor Pearcey who then takes the ribbon and feeds it into another machine]
Thank you. The program has now been put onto paper tape and we will put it onto the reader. For this purpose… for the purpose of this description there is no data on the paper tape. This tape reads the 12 holes row by row and is operated photoelectrically.
[Image changes to Dr Frank Hirst sitting at a console with buttons on it, image then shows paper tape going through the reader then shows a round screen filling up with a grid of dots, image then changes back to Dr Frank Hirst operating the console]
Dr Frank Hirst: We’re going to feed the tape now into CSIRAC and I press the appropriate control buttons on the console and the tape is inched forward until we position it into the buffer register at the right spot. Now the bootstrap tape is going in and the tape is moving into the reader. You can actually see it go into the memory filling up the cells of the memory. By switching on the console keyboard we can see the tape in position in store. It’s loaded in the memory and we now set the data for the problem and I am setting this on the keyboard registers. This is the number that has to be fed to the program. I fed that number into the machine and now the next number goes in and I start the button here and the calculation takes place and you’ll see the results coming out on punched paper tape from the paper tape punch at this stage.
[Image shows paper ribbon with holes punched through coming out of a metal box, then changes to show dots on the round oscilloscope screen]
Now I can see inside the memory tubes and watch the arithmetic registers in action. You can see the counting being done in the D Registers and you can see the accumulator calculating, adding and subtracting and so on. This array of cathode ray oscilloscopes is not evident on more modern machines. Because of the older type of machine these display tubes were present so one could do program testing.
[Image shows Dr Frank Hirst taking the punched paper ribbon out of a metal box and inserting it into the Flexowriter] Now we’re putting the results from that calculation into the Flexowriter which is going to print out the results for us and we feed it into the reading device here and we press the start read here and the tape will run into the Flexowriter and the printing of the codes on the tape now takes place.
This is a loan repayment schedule. The loan is being amortised over several years. This is the principal outstanding at the beginning of the first quarter. This column shows the interest at 6% payable for the quarter and this is the amount being paid off the loan. As the loan schedule goes of course the interest becomes less each quarter and the repayment is greater. And this is then done by the machine in a few minutes but on a desk machine of course it would take quite a long time. The program stays in the machine and a different loan can be calculated by just pressing the next parameters in for the loan amount.
[Image shows close up of numbers being printed on a piece of paper]
Now we’re coming to the final payment and the machine will add up the complete total of all the interest paid in the first column and the complete amount of money paid off the loan and this of course balances with the outstanding amount of the first quarter.
[Image changes to Dr Trevor Pearcey sitting at the control console]
Dr Trevor Pearcey: I have said that CSIRAC was easy to use. Let me illustrate by mentioning a few points of its design. From the operator’s point of view the display of the operations was comprehensive and convenient.
[Image changes to show display tubes with dots appearing and disappearing then pans to show a panel with small blinking light bulbs]
The state of the store and the arithmetical registers was shown as arrays of spots or traces on small cathode ray tubes and the state of the control system was made visible as rows of lights on the panels in front of the control console. A switchboard provided facilities for manual control of a program and for insertion of requisite data while the program was running other than the data, which was provided on the punched paper tapes.
[Image changes to show Dr Frank Hirst sitting at a desk with an open book]
Dr Frank Hirst: Well that is the story of CSIRAC. This machine, which is still in operation, is perhaps the oldest at present in the world and it is fitting that this machine is to be stored in the Applied Science section of the National Museum. It will be a historic exhibit and lots of people in the future should gain much information about early days in computing from the presence of CSIRAC in the museum. We are very pleased that it’s going there because this machine has been used for hundreds of computations in research projects and been used to teach many students in the University of Melbourne.
[New text appears: END]