Subj : Re: CPU Hog
To   : Ryan Fantus
From : fusion
Date : Mon Aug 08 2022 17:12:00

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> 
 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.

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