IBM's Standard Modular System (SMS) cards

 
I love SMS cards, they're so cute!

SMS is an acronym for "Standard Modular System", which are the small 114 x 67mm (approx. 4.5"x2.6") printed circuit boards used in IBM equipment from the late 1950's to the mid 1960s. As I understand it, SMS was developed during the amazing IBM 7030 "Stretch" project, as IBM's standard method of packaging transistorized circuitry. Even after they switched to the SLT (Solid Logic Technology) packaging for the System/360 in 1965, a few SMS cards still turned up inside IBM equipment, usually in the power supplies. 

An SMS card would typically have 3 to 6 germanium transistors and 15 or so resistors, plus half a dozen capacitors and diodes. A board might contain a flip-flop or a few simple gates, so each board roughly corresponds in function to a Small Scale Integrated (SSI) circuit of the early 1970's, such as one of the 7400 series chips, but about 30 times bigger.

Apparently, in 1955 when the SMS system was devised, the intention was that about 100 different card types would provide all the functions that IBM would need in any of its equipment, making design, manufacture and servicing more streamlined. But by 1960, there were about 2500 SMS card types!

When I was a kid, I bought a few hundred of these "computer boards" (as they were advertised) by mail order, and from surplus stores, as a cheap source of transistors. Why? For my own home built computer of course. Which never happened, didn't even come close, (because I had no idea what I was doing). I might have had more luck with that project if the boards I bought were usable, but they invariably had the edge connectors broken off, making them impractical as a "ready to use" part. I later realized the edge connectors had been broken off to reclaim the gold plating of the connector fingers.

Years later, when I acquired the insides of the 1401 and 7044 systems that were installed at Melbourne University, I suddenly had thousands of these things, and then it was ME breaking off the edge connectors for the gold. 
I thought they were pretty cute then too, and should have kept some. But I had gold fever...
 


The vast majority of SMS cards would have been low power logic circuits, forming part of the central processor of the machine they came from. These are from my 1401 Core Memory Frame, and are less typical, since their functions would have been be more analogue in nature, such as core drivers and sense amplifiers.

To get up close and personal with an SMS card, click the images below

   
The images above show both sides of two board types ("W X" and "AQV")
Two more boards types, "DKA" and "AQU"

 
These are IBM schematics for a couple of SMS cards circa 1960 (not any of the cards above).
Type DEF:  A quad 2 input NAnd gate 
(An SN7400 chip on a board!)

Type DHF: A dual JK Flip-Flop with output drivers 
(IBM calls a flip-flop a "trigger")


 
I wish I'd kept some of the thousands of SMS cards that I used to have in 1979, but I didn't.
If you have some that you don't really want, I'd love to hear from you!

 
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