The IAS machine was the first electronic digital computer built by the Institute for Advanced Study (IAS), Princeton, NJ, USA. The paper describing the design of the IAS machine was edited by John von Neumann.

The machine was a binary computer with a 40 bit word, storing two 20 bit instructions in each word. The memory was 1024 words. Negative numbers were represented in "two's complement" format. Two registers: the Accumulator (AC) and Multiplier/Quotient (MQ).

Importantly, the IAS machine was the first design to mix programs and data in a single memory. Von Neumann showed how the combination of instructions and data in one memory could be used to implement loops, by modifying branch instructions when a loop was completed, for example. The resultant demand that instructions and data placed on the memory later came to be known as the Von Neumann Bottleneck .

While the original design called for using a type of vacuum tubes called RCA Selectron tubes for the memory, problems with the development of these complex tubes forced the switch to Williams tubes.

IAS machine derivatives

Plans for the IAS machine were widely distributed to any school or company interested in computing machines, resulting in the construction of fifteen derivative (but incompatible) computers referred to as "IAS machines".

Some of these "IAS machines" were:

• AVIDAC (Argonne)
• CYCLONE (Iowa State University)
• ILLIAC I (University of Illinois)
• JOHNNIAC (RAND)
• MANIAC I (Los Alamos)
• MISTIC (Michigan State University)
• ORACLE (Oak Ridge)
• ORDVAC (Aberdeen Proving Ground)
• SILLIAC (University of Sydney)
• WEIZAC (Weizmann Institute)