!!! Overview [1] 
[{$pagename}], known as the Defense Calculator while in development, was announced to the public on April 29, [1952|Year 1952], and was [IBM]’s first commercial scientific computer.

Its business computer siblings were the IBM 702 and IBM 650. It was based on the IAS machine.[2]

The system used vacuum tube logic circuitry and electrostatic storage, consisting of 72 Williams tubes with a capacity of 1024 [bits] each, giving a total memory of 2048 words of 36 bits each. Each of the 72 Williams tubes was 3 inches in diameter. Memory could be expanded to a maximum of 4096 words of 36 bits by the addition of a second set of 72 Williams tubes or (later) by replacing the entire memory with magnetic core memory. The Williams tube memory and later core memory each had a memory cycle time of 12 microseconds. The Williams tube memory required periodic refreshing, mandating the insertion of refresh cycles into the [{$pagename}]'s timing. An addition operation required five 12-microsecond cycles, two of which were refresh cycles, while a multiplication or division operation required 38 cycles (456 microseconds).

Instructions were 18 bits long, single address.
* Sign (1 [bit]) - Whole word (-) or Half word (+) operand address
* Opcode (5 [bits]) - 32 instructions
* Address (12 [bits]) - 4096 Half word addresses
Numbers were either 36 [bits] or 18 [bits] long, signed magnitude, fixed point.

[{$pagename}] had only two programmer accessible registers:
* The accumulator was 38 [bits] long (adding two overflow bits).
* The multiplier/quotient was 36 [bits] long.

!! IBM 701 Emulator [2]
The world's best—probably only—IBM 701 emulator!

To make programming more convenient than it was in 1953, they added a couple of things that aren't part of the 701 itself: a log that shows the instructions and registers in real-time, and an assembler that automatically punches a card deck and loads it into the card reader. (The assembler doesn't run on the 701.)

!! Category
%%category [History]%%

!! More Information
There might be more information for this subject on one of the following:
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* [#1] - [IBM_701|Wikipedia:IBM_701|target='_blank'] - based on information obtained 2017-08-09- 
* [#2] - [IBM 701 Emulator|http://basepath.com/new/701/index.php|target='_blank'] - based on information obtained 2017-08-09-