This page describes the IBM SMS card "4Y", and is part of the SMS card database.

Function of the card:
Field replacement # 4

Part number: 370951

PCB number: 747203

Used in: IBM 2821 Control Unit

References: IBM 2821 CCD, p8
This page created by Ken Shirriff on Wed Sep 15 18:15:11 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.