1958: standard modular system
The plug-in cards exist in two different versions, as single width cards that are 2.5 inches in width and 4.5 inches in length or double with cards that are 5.375 inches in width and 4.5 inches in length. The pins of the SMS plug-in cards are plated with gold to guarantee a good conductivity. The modules were plugged in bigger panels to realize larger circuits, but the modules could also be changed whereby could be reached a better variability.
The back of the cards were produced mechanically while the front side was made by manual labor. Little programs and logical switches were stored and handled with these cards. When the concept of the SMS cards was developed, IBM banked on some hundred cards which were needed for replacing similar older systems. It turned out ton be wrong, as the number of developed cards surmounted 2500 units by far. Reasons are the wide variety of different systems and it demands.
