Re: Re: UMB and 386/486 --> status of FreeDOS emm386 etc.

Bart Oldeman <[email protected]>
Newsgroups gmane.os.freedos.devel
Message-ID <[email protected]> 
On Mon, 21 Oct 2002, Alain wrote:

> Please explain something to me: If I run some protected mode programs
> with _only_ fdxms (which dos not provide VCPI) they run. Why is it
> that such program will stop working?

Without EMM386 the CPU runs in real mode which means that protected mode
programs are able to switch to protected mode themselves. With EMM386
the CPU runs in V86 mode, a special form of protected mode, and the
programs are not allowed to escape V86, but need to politely ask the
monitor (i.e., EMM386). That mechanism is part of VCPI.

Without hardware support you simply cannot get UMBs in real mode.

Bart
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