Hi Shane,

summary of your mails...

C000: Video ROM.  At C900 are strings "S3 Corp." and "Trio64".
CC00:  PXE ROM by Argon Technologies
CD00 to EFFF apparently FF

DOS uses d008 to db99, xcdrom doslfn etc high
nothing in MEM /E, largest exe 623k, low 639k

Note that if accessing dc00 to efff would
trigger problems, you would not notice as
this area is not filled by you here...

NOEMS but no X option:
DOS uses cd08 to d899, similar comment to
previous, you do not fill d900 to efff so
that area might or might not be problematic.

JEMM386 seems to assume that the PXE ROM
ends at ccff, matching your "ff from cd00".

X option but no NOEMS:
largest exe 567k, EMS with page frame at d000
DOS does not seem to use any UMB at all, did
you forget DOS=HIGH,UMB here?

No X option and no NOEMS:
DOS just crashes, exception 0D at c800:11e5 etc

ss:esp at d0de:4, ebp=a0 ebx=7ff0007 edx=d1
esi=40fa0, edi=90fa0, ds=70, es=b800, fs=d1,
gs=f000, code: 9c 2e ff 1f... which is pushf or
pushfd followed by call far [cs:bx] or [cs:edi]

It is interesting that c800 is mentioned here,
leads to the question whether VGA ROM is only
c000-c7ff and some extra ROM is at c800-cbff?

The crash is a stack overflow with stack at
a location in d000 area but then your other
examples do use the d000 area for UMBs, odd.

The f000 ROM and b800 screen segments might
mean that something in ROM tried to display
a message when the stack overflow happened.
Then the original crash would have been at
some other place, not logged by jemm386...?

You could try to loadhigh / devicehigh some
more things to fill more of the UMB area to
get more insights about which areas are bad.


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