Card Edge Connectors [MCA]

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Louis Ohland

Oct 13, 2021, 9:46:46 PMOct 13

Marco Moock

Oct 14, 2021, 9:39:15 AMOct 14
Am Wed, 13 Oct 2021 20:45:55 -0500
schrieb Louis Ohland <>:

More information (including pictures) is available here:

Louis Ohland

Oct 14, 2021, 12:32:38 PMOct 14
Site only good for those that won't take time to learn anything. [IMHO]

"Despite the fact that MCA was a huge technical improvement over ISA, it
soon became clear that its introduction and marketing by IBM was poorly
handled. IBM had strong patents on Micro Channel architecture system
features, and required Micro Channel system manufacturers to pay a
licence fee - and actively pursued patents to block third parties from
selling unlicensed implementations of it. The PC clone market did not
want to pay royalties to IBM in order to use this new technology, and
stayed largely with the 16-bit AT bus, (embraced and renamed as ISA to
avoid IBM's "AT" trademark) and manual configuration, although the VESA
Local Bus (VLB) was briefly popular for Intel '486 machines. "

How much research did IBM put into MCA? Why should they allow cloners to
strip them of their IP?

Poor marketing, 'tis true. At the time of introduction [April '87] a
large chunk of systems ran DOS, single tasking. MCA, OTOH, was build
with features that made multi-tasking OSs better performing. So delays
by IBM to introduce OS/2 certainly didn't help demand.

IBM took significant strides toward ASICs, memory technologies, and
components. Much reduced demands for support. MCA design with POS darned
near eliminated jumpers on adapters. Fond memories of DMA / IRQ jumpers
on ISA cards down towards the edge connectors. Very painful to change
settings on a card that is in-between other installed cards.

"For servers the technical limitations of the old ISA were too great,
and, in late 1988, the "Gang of Nine", led by Compaq, announced a rival
high-performance bus - Extended Industry Standard Architecture (EISA).
This offered similar performance benefits to Micro Channel, but with the
twin advantage of being able to accept older ISA boards and being free
from IBM's control. "

This is stupidware.

Dropping an old ISA card into an EISA slot defeats the advanced features
of EISA, most notably IRQ sharing. The fantasy that old ISA cards were
being moved to newer systems en masse is wrong.

I think there is one good page on Github, but it's HTML-ization of a
Tech Manual.

Look at, MAJ Tom has straightened it up some,
but it isn't intuitive to us mere mortals.

Tom has done a bit o' painful hardware probing. BIOS level stuff.

We are here if you need help findting something.

Louis Ohland

Oct 14, 2021, 12:45:21 PMOct 14
Oh, before you think I'm pre-emptively nuking other sites, it
depends. Over the years, there has been plenty of bad tech writing by
IBM, wrong stuff by IBM, superseded information, whatever.

After years of calling the yellow / blue glass chips on processor
complexi as Synchrostream, and the thick aluminum capped chip whatever,
MAJ Tom did the complex pinout and determined the glass chip is the Bus
Interface Controller [BIC], and the thick aluminum capped chip is the
Synchrosream Controller [SSC].

So I looked at the Wiki page, and saw some "so what" stuff, some stuff
that's re-warmed sludge from the Internet, and stuff that doesn't quite
fit IBM's business model.

MCA is a journey, just a shame about the destination... ;)
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