From Newsgroup: comp.sys.ibm.ps2.hardware

Ladies and gentlemen, I can confidently report the existence of the
antithesis of the Idiot Savant, the Savant Idiot. We are all used to
Rainman intuitively grasping a complex subject.

A Savant Idiot, OTOH, can look at a complex subject, and come up with a totally useless question.

Anyways, my assertion of IBM just telling you how to use MCA without explaining the low-level mechanisms seems to be spot-on.

So, the vague question was can we get more than 256 colors over the AVE.

Two different scenarios, an 8580 and an 8595.

8580 has VGA on sysboard. The AVE can pass digital signals from the
on-board VGA over to the AVE adapter's DAC, thence to it's HDD15 -OR- it
can pass digital signals from the AVE adapter to the sysboard's DAC for
output to the sysboard HDD15.

In the first case, the on-board VGA can only output VGA to the AVE
adapter. In the second case, the AVE adapter -MIGHT- be able to do
better than VGA, but the sysboard's DAC [probably IMS-171] can't do
better than VGA.

Now lettuce peer into the tossed salad of the Model 95 which lacks
planar base video. The Model 95 has the Base Video slot [#5] and the
Auxiliary Video slot [#7].

The few snippets in the '92 video documentation says the Auxiliary Video Extension is disabled when the [XGA or XGA-NI] enters extended mode. So
my SWAG is that the AVE is software controlled via registers.

Unfortunately, searching for IBM "Auxiliary Video Extension" brings up
only one patent from IBM that uses something that is not the AVEC. That
is it. So much for a more thorough explanation...

Some Super High Intensity Tinkering here... The registers used by VGA to control the AVE are NOT used in that way by XGA when it enters extended
mode. So the Model 90 has an AVE slot, and as long as the planar XGA
stays in VGA mode, it can control and use the AVE. As soon as it enters
XGA extended modes, it cannot use the AVE.

Perhaps a non-XGA adapter could support the needed registers, but I'd
wager slim-to-none.
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