CSIRAC

CSIRAC

CSIRAC, Australia's first digital computer, as displayed at the Melbourne Museum
Also known as	CSIR Mk 1
Type	digital computer
Release date	c.1949 (1949)

CSIRAC (/ˈsaɪræk/; Council for Scientific and Industrial Research Automatic Computer), originally known as CSIR Mk 1, was Australia's first digital computer, and the fifth stored program computer in the world. It is the oldest surviving first-generation electronic computer (The Zuse Z4 at the Deutsches Museum is older, but was electro-mechanical, not electronic), and was one of the first in the world to play digital music.

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).