(Dr Frank Hirst) Trevor, how did it come that
you designed the machine with 16 D Registers?
(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.
(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.
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.
(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.
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.
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.
These take the form usually of pipes
containing mercury, each one about 5 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.
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.
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.
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.
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.
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.
(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.
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.
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.
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.
(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.
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.
(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.