On 08 Aug 2022, Ryan Fantus said the following...
RF> Ni> details of how it works. I do know that 64-bit x86 processors are abl
RF> Ni> to run 16-bit binaries when running in 32-bit mode though..
RF> Yep, ntvdm runs any time I launch a DOS program. It creates some
RF> overhead but seems to work more or less fine. *shrug*
the ntvdm pretends to be dos, emulates bios calls and all that.. but the 16-bit
code runs on a virtualized hardware cpu much like the modern vt-x extensions
virtualbox uses to speed up emulating newer oses. that 16bit virtualized cpu
mode is only accessable when the cpu itself is in 32bit mode.
ntvdm64 is a software emulator they borrowed from windows for.. powerpc? it
emulates both an intel cpu AND all the dos/bios stuff. i kinda wonder how well
it worked over there. could run a powerpc bbs? heh
another neat thing is each ntvdm gets it's own "640k" of ram, it's own
EMS/XMS, etc.. it's really the scaffolding of the single-pc multinode bbs.
it's neat stuff. bit of a shame the 16bit mode is not accessable from 64bit
oses.. but we're lucky it works in 32bit mode. in theory it should be faster
than the ntvdm64 one, but with modern cpus i don't know if you could measure
that difference anymore
... I think I am, therefore, I am... I think.
--- Mystic BBS v1.12 A47 2021/12/25 (Windows/32)
* Origin: cold fusion - cfbbs.net - grand rapids, mi
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