CSIRAC ( /ˈsaɪræk/; Council for Scientific and Industrial Research Automatic Computer), 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 and is one of only a few surviving first-generation computers (others include the Zuse Z4 and at least two Ferranti Pegasus computers).

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).

Trevor Pearcey (5 March 1919 – 27 January 1998) was a British-born Australian scientist, who created CSIRAC, one of the first ever stored-program electronic computers in the world.

Born in Woolwich, London, he graduated from Imperial College in 1940 with first class honours in physics and mathematics. He emigrated to Australia in 1945.

In a 1948 paper, he envisaged using a digital electronic computer for providing information over a national telecommunications network:

He bet that he could make an electronic device that would be 1000 times faster than the best electronic device of the time. Just one of his calculators filled a small room, weighing 7 tons.

He was awarded a D.Sc. by the University of Melbourne in 1971.

In his later years he lived on the Mornington Peninsula near Melbourne.

The Pearcey Foundation and the Pearcey Award for outstanding achievement by an Australian in the ICT industry are named after Trevor Pearcey.