The computer was constructed by a team led by Trevor Pearcey and Maston Beard, working in large part independently of similar efforts across Europe and the United States, and ran its first test program some time in November 1949.
The machine was fairly representative of first-generation valve-driven computer designs. It used acoustic delay lines as its primary store, with a typical capacity of 768 20-bit words (later doubled), supplemented by a magnetic drum with a total of 4,096 word capacity and an access time of 10 milliseconds. Its memory clock ran at 1000 Hz, with the control unit synchronized to that clock and initially taking cycles to execute an instruction (a later improvement sped up many instructions). The "bus" (termed the "digit trunk" in their design) is unusual compared to most computers in that it was serial - it transferred one bit at a time. The instruction set was minimal, but supported the basic set of arithmetic and logical operations, as well as conditional and relative jumps (making it possible to write a library of subroutines).
Input to the machine was performed in the form of punched paper tape, after experiments with punch cards proved unsatisfactory. The machine was controlled through a console which allowed programs to be stepped through one at a time, and featured CRT displays which showed the contents of registers. Output was through a standard teleprinter or to punch tape.
The machine, like all machines of the era, had no operating system. A high-level interpreted programming language called INTERPROGRAM was developed late in the machine's life by Geoff Hill. It was similar to early forms of BASIC, though preceded that language for some years.
In 1951, CSIRAC was used to play music, the first recorded use of a digital computer for the purpose.
In 1955, with the CSIR's decision that computing research was outside its purview, the machine was transferred from its home at the Radiophysics Laboratory at the CSIR in Sydney, to the University of Melbourne, where it served until 1961 as Australia's only academic computing facility. Many pioneers of computer use in Australia had their first exposure to computing there.
In 1961, CSIRAC was shut down for the last time. Its historical significance was already recognised at that stage, and it was placed in storage with plans for its later exhibition in a museum.
The machine was stored in a wharehouse through the 1960's and 1970's, before being set up for exhibit at a technical college from 1980 to 1992. It was then returned to storage.
Interest in the machine was revived in the 1990s, as it was realised that many of its developers were aging and precious history was being lost forever. A conference about the machine was held in 1996.
The machine finally found a permanent home in the Melbourne Museum in 2000. It has not been operable since its shutdown in 1961, but many of the programs that ran on it have been preserved, and an emulator has been written for it. The curators have decided that, aside from the huge cost of restoring the device, that the huge number of repairs that would be required to make it safe to operate (CSIRAC used 30 kilowatts of power in operation) would detract from its historical originality.
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