mid-sized computer Many IBM peripheral devices that are 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 have SLT-type hybrid ICs mounted on them
(see right). SMS cards are constructed of individual
discrete components mounted on single-sided paper-epoxy
printed circuit boards. Single-width cards are 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 are 5.375 inches wide by 4.5 inches tall, with two 16-pin gold plated edge connectors. Contacts are labeled
A–R (skipping
I and
O) on the first edge connector, and
S–Z, 1–8 on the second. The cards are plugged into a card-cage back-plane and edge connector contacts connected to
wire wrap pins. All interconnections are 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. Some card types can 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 is a two- to four-letter code embossed on the card (e.g.,
MX, ALQ). If the card has a "program cap" the code is 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 logic families were implemented (ECL, RTL, DTL, etc.) as well as
analog circuits, to meet the requirements of the many different systems in which the cards were used. File:IBM SMS card component side.jpg|SMS card from an IBM 1401 File:IBM SMS card circuit side.agr.jpg.jpg|Circuit side of same SMS card File:IBM SMS card, front.jpg|SMS card, front File:IBM SMS card, back.jpg|SMS card, back File:SMS card with power transistors.jpg|SMS card from an IBM 1401 File:IBM 1401 card cage 2.agr.jpg|IBM 1401 card cage File:IBM 1401 backplane.jpg|
Wire wrapped
backplane the same 1401 card cage File:IBM 7070.jpg|IBM 7070 card cage == See also ==