SILLIAC had its genesis in late 1953 when Harry Messel, the dynamic new head of the School of Physics, and John Blatt, newly arrived researcher, both independently realised that the School needed an electronic computer as a tool for theoretical physics. Whilst the first computer in the southern hemisphere, the CSIR Mk 1, was already running elsewhere on the University of Sydney grounds, there were several serious impediments to its use by the School of Physics: The CSIR Mk 1 was fully occupied with CSIR research and John Blatt found its staff very unhelpful; and, as a serial architecture computer, it was far too slow for the sort of problems that Blatt and Messel envisaged. The solution was for the School to build its own computer.
A suitable computer (ILLIAC) already existed at the University of Illinois and Blatt and Messel chose to copy it, rather than design a computer from scratch. The University of Illinois were happy to provide plans and assistance and estimated the cost of building a copy at US$110,000. John Algie, then maintenance engineer for CSIRAC, reviewed the costings and estimated the cost at AU£35,200 (roughly AU$2,000,000 in 2006 dollars). Based on this, a decision to proceed was made at the end of 1953. A mutual friend introduced Messel to Adolph Basser, who donated AU£50,000 towards the computer.
Like most of the IAS family, SILLIAC was not an exact copy of ILLIAC. One important change was the use of 2C51 valves in place of the more common 6J6. The 2C51 had been developed by Bell Labs for use in undersea telephone repeaters and had about 5 times the life (for 6 times the cost). This decision significantly improved the reliability of SILLIAC compared to its contemporaries.
Like other early computers, SILLIAC was physically large. The computer itself was a single large cabinet 2.5m high, 3m wide and 0.6m deep in one room. Its power supply occupied a second room and air-conditioning required an additional room in the basement.
On July 4, 1956, SILLIAC successfully passed its self test and a test run of a scientific program. On the following day, it ran its first "production" program and users were provided with regular access from July 9. The official opening was on September 12. Barry de Ferranti, a pioneer involved in the construction of SILLIAC described the main cabinet of the computer as about 2 metres high, 1 metre deep and 5 metres long with glass panels at the front and light switches that indicated what was going on inside. It ran until May 17, 1968 when it was replaced by a faster and bigger machine. SILLIAC has now been broken up into pieces.
In March 2008, the Australian Computer Museum Society was seeking alternate storage, or risk its collection including important components of SILLIAC being scrapped.