Editing IAS machine (section)

==Description==
The IAS machine was a [[Binary number|binary]] computer with a 40-bit [[Word (computer_architecture)|word]], storing two 20-bit instructions in each word. The memory was 1,024 words (5 kilobytes in modern terminology). Negative numbers were represented in [[two's complement]] format. It had two general-purpose [[Processor register|registers]] available: the Accumulator (AC) and Multiplier/Quotient (MQ). It used 1,700 vacuum tubes (triode types: 6J6, 5670, 5687, a few diodes: type 6AL5, 150 pentodes to drive the memory CRTs, and 41 CRTs (type: 5CP1A): 40 used as Williams tubes for memory plus one more to monitor the state of a memory tube).<ref name=Ware1953>[http://bitsavers.trailing-edge.com/pdf/rand/P-377_The_History_And_Development_Of_The_IAS_Computer_Mar53.pdf The history and development of the electronic computer project at the Institute for Advanced Study. Ware. 1953]</ref> The memory was originally designed for about 2,300 [[RCA]] [[Selectron tube|Selectron]] [[vacuum tube]]s. Problems with the development of these complex tubes forced the switch to [[Williams tube]]s.

It weighed about {{Convert|1000|lb|kg}}.<ref>{{Cite web|url=http://ed-thelen.org/comp-hist/BRL-i.html#IAS|title=IAS|last=Weik|first=Martin H.|date=December 1955|website=ed-thelen.org|series=A Survey of Domestic Electronic Digital Computing Systems}}</ref>

It was an [[asynchronous circuit|asynchronous]] machine, meaning that there was no central clock regulating the timing of the instructions. One instruction started executing when the previous one finished. The addition time was 62 [[microseconds]] and the multiplication time was 713 microseconds.

Although some claim the IAS machine was the first design to mix programs and data in a single memory, that had been implemented four years earlier by the 1948 [[Manchester Baby]].<ref name="University of Manchester">{{cite web|url=http://www.computer50.org/mark1/new.baby.html|title=Manchester Baby Computer|url-status=dead |archive-url=https://web.archive.org/web/20120604211339/http://www.computer50.org/mark1/new.baby.html|archive-date=2012-06-04}}</ref> The Soviet [[MESM]] also became operational prior to the IAS machine.

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 requirement that instructions, data and input/output be accessed via the same bus later came to be known as the [[Von Neumann architecture#Von Neumann bottleneck|Von Neumann bottleneck]].