Date:	Thu, 24 Feb 2000 12:07:11 +0200 (IST)
From:	Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
X-Sender:	eliz AT is
To:	Chris Jones <cj7 AT ukc DOT ac DOT uk>
cc:	djgpp AT delorie DOT com
Subject:	Re: Win 2000 & Djgpp
In-Reply-To:	<88udgt$74r$1@spruce.ukc.ac.uk>
Message-ID:	<Pine.SUN.3.91.1000224120633.13848E-100000@is>
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Reply-To:	djgpp AT delorie DOT com
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On Tue, 22 Feb 2000, Chris Jones wrote:

> But what I can't understand is when Win32
> programs crash Windows 9x completely - surely they are insulated much more
> than DOS apps, and shouldn't be able to do any damage at all.

Actually, it's the other way around: DOS apps are insulated from the
OS and from each other much more than Win32 apps.  That's because DOS
apps run in a different virtual machine (one each for every DOS box
you have open on your system), while Win32 apps all run in the same
VM, and share that VM with the kernel.

The extra level of insulation between different VMs is due to several
factors:

  - the description tables (LDTs) are not shared between VMs;
  - each VM uses a separate page directory.

In contrast, different Win32 apps running in system VM all share the
same LDT and the same page directory, the only insulation between them
being the page tables, which Windows switches when it multitasks
between Win32 apps.

- Raw text -