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).
Originally designed to use RCA Selectron tubes for the memory, problems with the development of these complex tubes forced the switch to Williams tubes.
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: