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CSIRAC, Australia's first digital computer, as displayed at the Melbourne Museum

CSIRAC (Council for Scientific and Industrial Research Automatic Computer, pronounced /ˈsаɪræk/), originally known as CSIR Mk 1, was Australia's first digital computer, and the fourth stored program computer in the world. It was first to play digital music[1][2] and is the only surviving first-generation computer.[3]

The CSIRAC 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 sometime in November 1949.

The machine was fairly representative of first-generation valve-driven computer designs. It used mercury acoustic delay lines as its primary data storage, with a typical capacity of 768 20-bit words (later doubled), supplemented by a parallel disk-type device with a total 1024-word capacity and an access time of 10 milliseconds. Its memory clock ran at 1000 Hz, and the control unit, synchronized to the clock, took two cycles to execute an instruction (later the speed was doubled to one cycle per instruction). 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 in 1960 by Geoff Hill. It was similar to early forms of BASIC, which was designed in 1963 for the 20-bit transistorized GE-200 series.

In 1950 or 1951, CSIRAC was used to play music, the first known use of a digital computer for the purpose. The music was never recorded, but it has been accurately reconstructed (reference 2).

CSIRAC, side view

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 formed Australia's only academic computing facility until late 1956. Many pioneers of computer use in Australia had their first exposure to computing there.

Most of CSIRAC's approximately 2000 valves were of the types 6SN7[4], 6V6[5], EA50 Diodes and KT66.[6] George Semkiw later redesigned the drum read electronics to use germanium transistors.

In 1964, 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 warehouse through the 1960s and 1970s, before being set up for exhibit at Caulfield Institute of Technology[7] 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, 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 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.

Defining characteristics of some early digital computers of the 1940s (In the history of computing hardware)
Name First operational Numeral system Computing mechanism Programming Turing complete
Zuse Z3 (Germany) May 1941 Binary Electro-mechanical Program-controlled by punched film stock (but no conditional branch) Yes (1998)
Atanasoff–Berry Computer (US) 1942 Binary Electronic Not programmable—single purpose No
Colossus Mark 1 (UK) February 1944 Binary Electronic Program-controlled by patch cables and switches No
Harvard Mark I – IBM ASCC (US) May 1944 Decimal Electro-mechanical Program-controlled by 24-channel punched paper tape (but no conditional branch) No
Colossus Mark 2 (UK) June 1944 Binary Electronic Program-controlled by patch cables and switches No
ENIAC (US) July 1946 Decimal Electronic Program-controlled by patch cables and switches Yes
Manchester Small-Scale Experimental Machine (Baby) (UK) June 1948 Binary Electronic Stored-program in Williams cathode ray tube memory Yes
Modified ENIAC (US) September 1948 Decimal Electronic Program-controlled by patch cables and switches plus a primitive read-only stored programming mechanism using the Function Tables as program ROM Yes
EDSAC (UK) May 1949 Binary Electronic Stored-program in mercury delay line memory Yes
Manchester Mark 1 (UK) October 1949 Binary Electronic Stored-program in Williams cathode ray tube memory and magnetic drum memory Yes
CSIRAC (Australia) November 1949 Binary Electronic Stored-program in mercury delay line memory Yes

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