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IBM 701 Plugable Modules

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IBM 701 Plug-in Unit

figure 1.

The 701's vacuum tubes were collected into "pluggable units", a concept introduced with IBM's  604. The 701 was developed in 1952 in the Poughkeepsie Laboratory. The 701 known as the Defense Calculator. The 701's used 18-bit instructions, with maximum,  memory of 4096 words of 36-bits. It used Williams tubes or magnetic core memory which had a cycle time1 of 12 microseconds, and could do 2000 Multiplies and Divides per second. 

 

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Photo from an IBM ad in CACM Vol.18 No. 8, Aug 1975, caption: "Bill Stringfellow explains how the use of a special tool, an eight-tube pluggable unit, was set into a 701 computer. Alongside is an integrated circuit many times smaller, which performs comparable logic functions thousands of times faster in today's System/370."

figure 2.

 

 

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figures 3 and 4

 

 

  1. Memory cycle time refers to the minimum period between two successive requests.