Evolution of IBM packaging technology

The methods used by IBM to package electronics into their machines has evolved over several generations from the late 1950's to the early 1990's, each resulting in ever higher circuit densities.

SMS Cards
The SMS (Standard Modular System) was developed during the Stretch project in the late 1950's.  SMS provided low density packaging for IBM's new transistorized circuitry.

SLT Cards
With System/360 in 1964, came SLT (Solid Logic Technology) which consisted of small hybrid chips, and a new type of circuit board, as shown on the left. The other card on the right is from System/370 about 1970, and employs true integrated circuits on a larger board.
 Inside an SLT circuit package
The SLT form factor continued to be used through the 1970's, with Large Scale Integration (LSI) chips and larger card sizes.
SLT packaging culminated in high density cards with VLSI chips. This is from an IBM 4341 CPU. Some SLT cards were quite weird, this is from a System/370.
SLT cards were plugged into "boards". (which were always this size). About a dozen boards were mounted on a hinged "gate". And up to 4 gates were mounted in a "frame" (cabinet) 

Multi-Chip TCM's - 4381
This is part of the CPU from an IBM 4381 mainframe. There were about 30 of these modules in the machine. The heatsink, removed on the right, is a single piece of convoluted metal.

IBM 9121 TCM - Socket 2772!
This is part of the CPU from an IBM ES/9000 series mainframe. I think it was a 9121, and there were two of these subassemblies. The connections to the rest of the machine.
With its huge heatsink removed, one of the two TCMs (Thermal Conducting Module) is visible. The TCMs are held in place by four spring loaded clips.
The TCM removed. It weighs 2.3 kilograms (5 lbs). There are 2772 pins on the module, compare this with Socket 420 used on CPU modules in a PC.
After removing the 24 bolts holding the module halves together, we see the ceramic chip mounting substrate and the heat conduction pistons. There are sites for 121 chips on the substrate, this module has seven free sites. Each chip is about 8mm square. The small dots are also chips (bypass capacitors?)
Here three of the pistons are free, so that the springs in the cylinders are visible. The module was filled with a thick, sticky fluid to lubricate the pistons and help with heat conduction. (hopefully this stuff is non-toxic)

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