CSIRAC

CSIRAC

CSIRAC — the Commonwealth Scientific and Industrial Research Automatic Computer, pronounced "sigh-rack" — is Australia's first digital computer and the fifth stored-program computer in the world. Trevor Pearcey and Maston Beard built it in Sydney as the CSIR Mk 1, largely independent of the parallel American and British efforts, and it ran its first test program — a multiplication — sometime in November 1949.^[1]

Its lasting claim is stranger and better than "first Australian computer," though. CSIRAC is the oldest surviving first-generation electronic computer — not a reconstruction, not a replica, but the actual machine, displayed intact at Museums Victoria (moved to Scienceworks in 2018). Every other machine of its generation is a photograph or a rebuild; CSIRAC still exists because nobody threw it away.^[2]

A serial machine of mercury and valves

The design was representative of first-generation valve computing with a few quirks of its own:

• Memory: mercury acoustic delay lines — 768 20-bit words typical — plus a magnetic drum holding 4,096 words at 10 ms access. The memory clock ran at 1 kHz.
• Valves: roughly 2,000 of them — 6SN7 triodes, 6V6 and KT66 tetrodes, EA50 diodes.
• Bus: unusual for the era — the "digit trunk" was serial, moving one bit at a time.
• Instructions: a 5-bit destination, 5-bit source, and 10-bit address — 1,024 possible source/destination combinations, of which about 256 saw real use.
• I/O: 12-track punched paper tape in, teleprinter or punched tape out; the console had CRT displays showing register contents and could step programs one instruction at a time.^[3]

The machine moved to Melbourne in 1955 (where it picked up the name CSIRAC), ran weather forecasts and engineering calculations, and was retired in November 1964. In 1960 it even gained a high-level language — Geoff Hill's INTERPROGRAM, an interpreted notation similar to early BASIC — making CSIRAC one of the first machines anywhere to run something resembling a scripting language.^[4]

The first computer to sing

In 1950–51 CSIRAC became the first computer known to play digital music — programmers discovered that the timing of the machine's speaker pulses could produce pitched tones, and it publicly played Colonel Bogey at Australia's first conference on automatic computing machines in Sydney, August 1951. Decades before anyone wrote a tracker, a room full of mathematicians listened to a valve computer play a march. The recording of it survives.^[5]

Where it sits

CSIRAC belongs to the small club of first-generation machines that still exist — and it heads that list. Built in isolation on the far side of the world, retired intact, and still sitting in a Melbourne gallery, it is the rare early computer you can walk up to. EDSAC, the Baby, and ENIAC are reconstructions and fragments; CSIRAC is the machine itself.

Check your understanding

• What was CSIRAC originally called, and when did it first run?
• What made its main memory physically work — and how much did it hold?
• What is CSIRAC's unique status among first-generation computers?
• What did CSIRAC do in August 1951 that no computer had done before?