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RussHolsclaw (talk | contribs) Add information about 360 peripherals that used SMS, and use of wire-wrap for interconnections |
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{{Other uses|IBM SMS}}
[[File:SMScard.jpg|thumb|A single width SMS card.]]
The '''Standard Modular System (SMS)''' was a system of standard [[transistor]]ized circuit boards and mounting racks developed by [[IBM]] in the late 1950s, originally for the [[IBM 7030 Stretch]].{{Citation needed|date=May 2010}} They were used throughout IBM's second generation computers and peripherals, including its first transistorized calculator, the [[IBM 608]],<ref>http://www.columbia.edu/acis/history/608.html</ref> and the [[IBM 700/7000 series|7000]] and [[IBM 1400 series|1400]] lines and the [[IBM 1620|1620]]. SMS was superseded by [[Solid Logic Technology]] (SLT) introduced with [[System/360]] in 1964, however they remained in use with legacy systems through the 1970s.
Many IBM peripheral devices that were part of System/360, but were adapted from second-generation designs, continued to use SMS circuitry instead of the newer SLT. These included the 240x-series tape drives and controllers, the 2540 card reader/punch and 1403N1 printer, and the 2821 Integrated Control Unit for the 1403 and 2540. A few SMS cards used in System/360 peripheral devices even had SLT-type hybrid IC's mounted on them.
SMS cards were constructed of individual [[discrete component]]s mounted on single sided paper-epoxy [[printed circuit]] boards. Single width cards were 2.5 inches wide by 4.5 inches tall by 0.056 inches thick, with a 16 pin [[gold]] plated [[edge connector]]. Double width cards were 5.375 inches wide by 4.5 inches tall, with two 16 pin gold plated edge connectors. Contacts were labeled ''A–R'' (skipping ''I'' and ''O'') on the first edge connector, and ''S–Z, 1–8'' on the second.
The cards were plugged into a card-cage back-plane and edge connector pins connected to wire-wrap pins. All interconnections were made with wire-wrapped connections, except for power buss lines. The back-plane wire-wrap connections were mostly made at the factory with automated equipment, but the wire-wrap technology facilitated field-installation of engineering changes by customer engineers.
Some card types could be customized via a "program cap" (a double rail metal jumper bar with 15 connections) that could be cut to change the circuit configuration. Card types with a "program cap" came with it precut for the standard configuration and if a Customer Engineer needed a different configuration in the field he could make additional cuts as needed. This feature was intended to reduce the number of different card types a Customer Engineer had to carry with him to the customer's site.
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