Standard Modular System

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.

SMS cards are constructed of individual discrete components mounted on single-sided paper-epoxy printed circuit boards.

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.

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.

Part of the reason for the growth was that multiple digital logic families were implemented (ECL, RTL, DTL, etc.)