Visual Basic Question

Guy Dawson guy at
Thu Apr 23 01:57:12 CDT 2015

At work we're still running a QuickBasic DOS app in Windows 7 32bit using
WOW.EXE and NTVDM.EXE. Vista and Win7 did change some things that caused us
problems but they were things like write access to the root of the C drive.

The 64 bit versions of Vista and Win 7 don't have any WOW.EXE or NTVDM.EXE
at all.

On 23 April 2015 at 01:52, <mark at> wrote:

> >> The phrase "standard Windows 16bit DLLs" means Windows 3.1 DLLs. Such
> >> DLL's no longer work in a modern windows. If they directly access the
> >> hardware then they will not work on any NT based windows such as
> >> Windows/2000, Windows/XP, Vista, or 7, 8 or 9. Nor will they work on any
> >> 64-Bit windows full stop. 64-Bit windows does not support 16-bit code.
> >> If you have a Windows/95, 98 or ME environment then the code may work.
> >
> >They should work with 32 bit versions of windows as the 16 bit thunking
> >layer is still present.  YMMV of course.
> Actually, VB3 works perfectly well under all 32-bit versions of Windows up
> through XP; it breaks at Windows 7 (and presumably Vista).  Under all the
> NT-based versions (NT, 2000, and XP), Windows launches a virtual machine
> call NTVDM.EXE (NT Virtual DOS Machine), upon which runs yet another
> emulator WOW.EXE (Windows on Windows).  This latter emulator presents the
> non-preemptive message-passing architecture of Windows 3.1 to all the
> 16-bit Windows applications (like VB3) that run upon it.
> This actually worked remarkably well; I’ve personally supported an
> application for 20 years that is written in VB3, including adding new
> features all that time – even a Web server!  There was also a technique
> that allowed calling 32-bit DLLs from the 16-bit application.  There were a
> couple of bugs, of course, but generally it was a very stable solution to
> supporting legacy code.  There was even a work-around to NT’s rigorous
> defense of direct hardware access which continued to work through XP.
> Windows 7 broke all that.  (Presumably Vista actually did, but I’ve never
> seen a Vista system in the wild...)
> ~~
> Mark Moulding

4.4 > 5.4

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