Wikipedia has an overview of the SMS Card Techology.

This IBM publication provides in-depth technical information about the SMS cards.

A great source of detailed information about individual IBM SMS cards is the incredible blog of Ken Shirriff.

This document contains some SMS functional details: https://bitsavers.org/pdf/ibm/1620/fe/227-5647-0_1620_E_Level_CE_Manual_of_Instruction_1962.pdf