It was built at the Weizmann Institute during 1954-1955, based on the Institute for Advanced Study (IAS) architecture developed by John von Neumann. The WEIZAC was operational until December 29, 1963, and was superseded by a CDC 1604A computer. The 1604A was later superseded by the locally designed GOLEM.
As with all computers of its era, it was a one of a kind machine that could not exchange programs with other computers (even other IAS machines).
The WEIZAC project was initiated by Prof. Chaim L. Pekeris, who worked at the IAS at the time von Neumann's IAS machine was being designed. Chaim Weizmann, Israel's future first president, asked Pekeris to establish the Department of Applied Mathematics at the Weizmann Institute, and Pekeris wanted to have a similar computer available there. Pekeris wanted it as means to solve Laplace’s tidal equations for the Earth's oceans, and also for the benefit of the entire scientific community of Israel, including the Defense Ministry.
In July 1947, an advisory committee for the Applied Mathematics Department discussed the plan to build the computer. Among the committee's members were Albert Einstein, who did not find the idea reasonable, and John von Neumann, who supported it. In one conversation, von Neumann was asked; "What will that tiny country do with an electric computer?" He responded, "Don’t worry about that problem. If nobody else uses the computer, Pekeris will use it full time!"
In the end, a decision was made to proceed with the plan. Chaim Weizmann assigned $50,000 for the project – 20% of the Weizmann Institute total budget.
In 1952, Gerald Estrin, a research engineer from the von Neumann project, was chosen to lead the project. He came to Israel along with his wife, Thelma, who was an electrical engineer and also involved in the project. They brought with them schematics, but no parts. Estrin later commented: "As I look back now, if we had systematically laid out a detailed plan of execution we would probably have aborted the project." After arriving, Estrin's impression was that besides Pekeris, other Israeli scientists thought it is ridiculous to build a computer in Israel.
To recruit skilled staff for the project, a newspaper advertisement was posted. Most of the applicants had no records of prior education because those were lost in the Holocaust or during immigration, but in Israel's budding technical community everyone knew or knew about everybody else. The WEIZAC project also provided an opportunity for mathematicians and engineers to move to Israel without sacrificing their professional careers.
WEIZAC was an asynchronous computer operating on 40-bit words. Instructions consisted of twenty bits: an eight-bit instruction code and twelve bits for addressing. Punched paper tape was used for I/O, and later, in 1958, magnetic tape. The memory was initially a magnetic drum containing 1,024 words, and was later replaced with a faster 4,096 word memory. In 1961 the memory was further expanded with two additional 4,096 word modules.
In late 1955, WEIZAC performed its first calculation. Subsequently, it was used to study problems like worldwide changes in tide, earthquakes, atomic spectroscopy, X-ray crystallography, random walk methods, numerical analysis and more. The computer found out that there was an amphidromic point in the South Atlantic at which the tide does not change. It also numerically calculated the eigenvalues of a two-electron atom quantum system based on programming by Yigal Accad who put Pekeris' development of the relevant equations into machine code.  These results were later experimentally verified by the Brookhaven National Laboratory, confirming the correctness of Schrödinger's Equations.
WEIZAC was kept constantly busy, and users (especially from other institutions) became increasingly frustrated with not being able to get computing time, and demanded more computers to become available. WEIZAC's success led to the recognition of the demand for computers and digital technology in Israel, and ultimately, provided the foundation for Israel's computer and technology industries.
- "Computer Studies - News, Features and Discoveries from the Weizmann Institute of Science". Weizmann Wonder Wander. 2015-08-30. Retrieved 2017-11-28.
- Milestones: WEIZAC Computer IEEE. Retrieved 2010-03-25
- le-madaʻ, Mekhon Ṿaitsman (1962). Scientific Activities. The Institute. p. 19.
- The 1958 Pekeris-Accad-WEIZAC Ground-Breaking Collaboration that Computed Ground States of Two-Electron Atoms (and its 2010 Redux), Christoph Koutschan, Doron Zeilberger, https://arxiv.org/abs/1006.0200
- Bogdanowicz, Anna (5 December 2006) Middle East's First Computer Named History Milestone. IEEE. Retrieved 2010-03-25
- The WEIZAC Years (1954-1963), Gerald Estrin, IEEE Annals of the History of Computing, vol. 13, no. 4, pp. 317-339, Oct-Dec 1991. ISSN 1058-6180.
|Wikimedia Commons has media related to WEIZAC.|
- Weizmann Institute Computer Studies – With a historical overview including the WEIZAC.
- IEEE History Center: WEIZAC Computer, 1955
- Remembering WEIZAC: the beginning of computing in Israel, in Google's official blog
- WEIZAC: Israel's first computer – Prof. Aviezri Fraenkel recounts WEIZAC's beginning (video)