Click to enlarge IBM has always been at the forefront of electronics packaging technology, even their valve computers used modular construction. When they embarked upon the STRETCH project in the late 1950's, they specified a standard card construction for transistorised machines that lasted well into the 1960's. It was called the Standard Modular System, or SMS, and utilised single sided paper-phenolic printed circuit boards about 4 and 1/2 inches by 2 and 1/2 inches, with a 16 pin edge connector. Each board held up to about eight transistors and was roughly equivalent to a small-scale integration 74xx chip. The boards were inserted in sockets on racks, that IBM referred to as gates.

Click to enlarge The top image on the right shows one of my SMS cards, and the one below it shows eight cards plugged into their wire-wrap sockets, click on the thumbnail images of the card to see a larger version of either.

SMS was a victim of its own success. It was originally planned that only a couple of hundred card types would exist, but in the end thousands were produced, of all types, many with no transistors on them. Click here to read more about SMS. These cards can still be found quite readily, but often the edge connectors have been broken off in order to recover the gold plating.

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SMS was superseded when IBM developed a low-level of hybrid integrated logic, in 16-pin packages on a ceramic substrate. These were soldered onto multi-layer fibreglass cards with a complete grid of possible through-holes and new connectors. The whole new packaging was called solid-logic technology, SLT. The image on the left shows the component side of one of my SLT boards, click on the image of the card to see a larger version. However, SMS refused to die, and it is possible to find SMS boards with SLT chips on them.

IBM went on to develop ever higher levels of circuit integration but the more modern ones are too recent to interest me :-)

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