ILLIAC (Illinois Automatic Computer ) is the name of a series of mainframe computers that were built 1951-1974 and take their name from the University of Illinois, where the first computer was built in the series.

End of the 1940s were carried out as in many other places in the United States at the University of Illinois development work for computer according to the submitted by John von Neumann and other concept ( First Draft Report on the EDVAC, 1945, Von Neumann architecture). The result was the ORDVAC, the 1951 delivered to the Ballistic Research Center of the U.S. Army at Aberdeen Proving Ground. This prompted the order for another computer, the Illiac I, which was in September 1952 in operation and the first computer with Von Neumann architecture at an American University.

The Illiac I followed the same design as the ORDVAC, had 2800 vacuum tubes and a drum memory. She was in operation until 1963.

1962 was the successor, the Illiac II into operation, which was fully transistorized and had a pipeline architecture. The design work began in 1958, one of the computer architect was Donald B. Gillies, who was using the computer and to search for Mersenne primes and then thus set a record prime number.

The Illiac III was a SIMD computer specifically for image processing, first of bubble chamber photographs, then in biology. She went into operation in 1966, but was destroyed by a fire in 1968.

The Illiac IV was one of the first parallel computer. He was from the vector processor type with up to 256 processors. The development work continued for over 10 years, and was completed when the computer 1976, he was overtaken by technological development ( Cray -1 supercomputer ). The Illiac IV arose from the Solomon Project at Westinghouse, whose chief designer David Slotnick after the end of the project went to Burroughs and nudged the development in collaboration with the University of Illinois. After the first draft in 1966 there were multiple delays, among other things, student unrest in the late 1960s, the 1970 relocation of the development center according to Moffett Field in California (Ames Research Center NASA ) investigation. Then there were problems with the reliability, so your computer even after the official completion in 1972 until 1975, was fully functional. Until about 1981, it was for the special and well- parallelizable hydrodynamics problems, for which it was used at NASA, the fastest computer in the world. In 1982, she went out of service. Burroughs used the technology is still in its parallel element processing ensemble ( PEPE ) for the U.S. Department of Defense, that in case of emergency should calculate the orbits of shots fired on the U.S. ICBM 's. Experience with the Illiac IV influenced the early parallel computing research. The Illiac IV was also the first computer where the memory consisted only of semiconductor devices.

Even after several supercomputers were provided projects the University of Illinois by the name of ILLIAC, for example, the CEDAR project by David Kuck, a 1988 finished symmetrical multiprocessing system (sometimes ILLIAC V ) informed the ILLIAC 6 of 2005 or the Linux cluster Trusted Illiac of, 2006.