Restoring IBM (was: Age)

Eric Smith eric at
Tue Mar 1 13:15:54 CST 2005

wai-sun wrote:
> As I'm totally alien to the world of IBM classic mainframes, what
> exactly is a hybrid SLT module? Is it those square rectangular
> thingies on a small module which is laid out in a matrix-like
> formation?

A hybrid SLT module is one of the square metal cans, yes.  SLT is
"Solid Logic Technology".  It replaced the earlier SMS (Standard
Modular System) modules, which were more conventional circuit boards.

> What is inside? Potted discrete components or early ICs?

It's a hybrid circuit on a ceramic substrate.  Resistors, capacitors,
and inductors are printed/layered onto the substrate.  Diodes and
transistors are fabricated separately, directly bonded to the
substrate, and glass encapsulated.

The entire module is an "early IC", though not of the monolithic

For more details, see the IBM Journal of Research and Development,
April 1964:

SLT was replaced by MST (Monolithic System Technology) for the
System/370 in the early 1970s, though SLT continued to be used in
peripherals for some time:


More information about the cctalk mailing list