Standard Modular System: Difference between revisions

Revision as of 19:00, 20 September 2016

Revision as of 21:39, 5 April 2017

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[[File:SMScard.jpg|thumb|A single-width SMS card.]]

[[File:IBM 1401 card cage.agr.jpg|thumb|SMS cards in an [[IBM 1401]] mid-size computer.]]

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]].<ref>{{cite web|url=http://www.computer-museum.ru/books/archiv/ibm36040.pdf#page=18 |title=The 360 Revolution |last=Boyer |first=Chuck |date=April 2004 |publisher=IBM |pagespage=18 |accessdate=25 November 2013}}</ref> They were used throughout IBM's second generation computers, peripherals, the [[IBM 700/7000 series|7000 series]], the [[IBM 1400 series|1400 series]], 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 SMS was superseded by [[Solid Logic Technology]] (SLT) introduced with [[System/360]] in 1964, however they remained in use with legacy systems through the 1970s.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 [[IBN 2400|240x-series tape drives]] and controllers, the [[IBM 2540|2540 card reader/punch]] and [[IBM 1403|1403N1 printer]], and the [[IBM 2821 Control Unit|2821 Integrated Control Unit]] for the 1403 and 2540. A few SMS cards used in System/360 peripheral devices even had SLT-type hybrid ICs mounted on them.

SMS cards were constructed of individual [[discrete component]]s mounted on single-sided paper-epoxy [[printed circuit board]]s. Single-width cards were 2.5&nbsp;inches wide by 4.5&nbsp;inches tall by 0.056&nbsp;inches thick, with a 16 -pin [[gold plated]] plated [[edge connector]]. Double width cards were 5.375&nbsp;inches wide by 4.5&nbsp;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 contacts connected to [[wire wrap]] pins. All interconnections were made with wire-wrapped connections, except for power bus 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.

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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.

The card type was a two to four letter code imbossedembossed on the card (e.g., ''MX, ALQ''). If the card had a "program cap" the code was split into a two letter card type code and a two letter "cap connection" code (e.g., ''AK ZZ'').

When SMS was originally developed, IBM anticipated a set of a couple hundred standard card types would be all that would be needed, making design, manufacture and servicing simpler. Unfortunately that proved far too optimistic as the number of different SMS card types soon grew to well over 2500. Part of the reason for the growth was that multiple [[Digital data|digital]] [[logic families]] were implemented (ECL, RTL, DTL, etc.) as well as [[analog circuit]]s, to meet the requirements of the many different systems the cards were used in.