512 vs 640 K

[Aryeh M. Weiss]

In article <97 at mq.com> alan at mq.com (Alan H. Mintz) writes:
>The question is, will XENIX install and run correctly on a machine that has
>it's memory mapped for 512K base and the rest above 1 meg ?

Yes it installs and runs.  I have done this many times.  We have several
true blue (IBM) AT's which we upgraded with Intel 386 boards with 3MB.
The motherboard has 512K of base; the Intel board memory starts at the 
1MB address.  Xenix runs fine.

>When we sell a machine with 16 Megs of memory and VGA, it is tough to find 
>address space for accessories (like more than two SI cards). Losing 128K
>of memory out of 16Mb is nothing compared to the benefit of another 128K
>of available address space!

I have never seen a commercial i/o card which is configurable outside the
A0000-FFFFF area, but that doesn't mean they don't exist.  Also I do not
know what typical BIOS memory sizing algorithms do, but you may run into
config problems if a i/o card maps its memory starting at address 0x80000 
and the BIOS decides it is general purpose RAM.
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