In article <9603221548.AA25664@cthulhu>,
Mike Long  <mike.long@analog.com> wrote:
> The A20 gate is one of those little featureoids that litter the PC AT
> "architecture".  When IBM was designing the PC AT, they found that
> if you use a segment:offset address that add to > 1 megabyte, then the
> 286 accesses memory beyond 1 megabyte.  The A20 gate is a simple AND
> gate that they added to disable the processor's A20 address line.
> With A20 disabled the AT could mimic the 8086, which wraps around to
> low memory.  On powerup, A20 is disabled; you have to issue a command
> to the keyboard controller to enable it.

I know that on some machines, HIMEM.SYS needs a switch (/machine:N with
some N) for something to do with A20. Does NetBSD (or the bootblocks)
know or care about this?

Charles, the machine I'm having troubles with the sea driver needs
/machine:1 for HIMEM.SYS. I forgot to mention that in the PR. Could
that possibly be related in any way? I don't see how it would, but I
thought I should mention it. Will it cause me any other problems?