This page describes the IBM SMS card "TDD", and is part of the SMS card database.

Function of the card:
SDTDL-sdtrl - 115 kc oscillator
SDTDL-SDTRL- 115 KC Oscillator

Listed in 1401 SMS card usage

Saturated Drift Transistor Diode Logic (SDTDL) is a form of Diode-transistor logic using faster drift-field transistors.

Saturated Drift Transistor Resistor Logic (SDTRL) is a form of resistor-transistor logic using faster drift-field transistors.

Part number: 370400

PCB number: 484149

Used in: IBM 1401, IBM 1410

IBM SMS card type TDD 370400

Image courtesy of Philipp Müller

References: 1410_SMS_VOL_1.pdf, p111
Coslet data
2_2 SMS Cards, pp125,126
This page created by Ken Shirriff on Wed Sep 15 18:15:10 2021.

The information on these pages comes from a variety of sources, especially old IBM documents on, as well as information from the IBM 1401 restoration team, especially Tim Coslet's SMS data and Jim Hunt's data. Much of this information was obtained through OCR, so don't expect complete accuracy. These pages are not associated with IBM in any way.