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Groups > comp.os.msdos.programmer > #288
| From | Ross Ridge <rridge@csclub.uwaterloo.ca> |
|---|---|
| Newsgroups | comp.os.msdos.programmer, comp.os.msdos.misc, alt.msdos |
| Subject | Re: What role does "DOS" play in Windows 95/98? |
| Date | 2011-10-17 12:46 -0400 |
| Organization | University of Waterloo |
| Message-ID | <j7hm5v$2rt$1@rumours.uwaterloo.ca> (permalink) |
| References | <4E9B5A53.392C9558@Guy.com> |
Cross-posted to 3 groups.
DOS Guy <DOS@Guy.com> wrote: >Many people believe that Windows 95/98 runs "on top of" DOS. Yes and no. Windows 95 starts of by booting real-mode MS-DOS pretty much normally. Then it starts VMM (Virtual Machine Manager), a 32-bit ring 0 environment for creating virtual machines (VMs) that running cloned versions of the MS-DOS enviroment that booted the PC. VMM is essentially a operating system to itself, with its own drivers (VxDs) and you can argue this actually what Windows 95 runs on top of. VMM then creates a VM for running "Windows" in. Both 16-bit and 32-bit Windows applications run as ring 3 protected mode applications in this single VM. When a Windows application does some sort of device access, like read from a disk, the request gets passed to VMM. If the VMM has a suitable device driver then it handles the request itself. If not then the VMM can use the cloned MS-DOS environment to handle it. It switches the processor to Virtual 8086 mode, a protected mode enviroment where instructions are decoded like in real-mode. It can then use MS-DOS and/or the BIOS to handle the request, without actually giving up control of the machine. Since MS-DOS acts as as device driver of last resort for the VMM, you could also argue that Windows 95 is running on top of MS-DOS. Note that ability to use MS-DOS and the BIOS like this is what allows Windows 95/98/ME to work all sort devices on all sorts of PCs, even ones without driver support. That includes modern devices that didn't even exist when these operating systems were released, at least those that the BIOS has support for. MS-DOS applications running under Windows 95 get their own VMs, seperate from the main VM used to running Windows. Real-mode MS-DOS applications run in Virtual 8086 mode, however things disk and other device accesses go through the VMM like with Windows applications. Note that this is how Windows has worked in "enhanced mode" since support for it was added in Windows/386 2.1. Ross Ridge -- l/ // Ross Ridge -- The Great HTMU [oo][oo] rridge@csclub.uwaterloo.ca -()-/()/ http://www.csclub.uwaterloo.ca/~rridge/ db //
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What role does "DOS" play in Windows 95/98? DOS Guy <DOS@Guy.com> - 2011-10-16 18:27 -0400
Re: What role does "DOS" play in Windows 95/98? Trifle Menot <triflemenot@beewyz.com> - 2011-10-16 23:38 +0000
Re: What role does "DOS" play in Windows 95/98? "Rod Pemberton" <do_not_have@noavailemail.cmm> - 2011-10-17 05:16 -0400
Re: What role does "DOS" play in Windows 95/98? "Klaus Meinhard" <K_Meinhard@gmx.de> - 2011-10-17 16:47 +0200
Re: What role does "DOS" play in Windows 95/98? tomdzip <tomdzip@hotmail.com> - 2011-10-17 09:02 -0700
Re: What role does "DOS" play in Windows 95/98? "Klaus Meinhard" <K_Meinhard@gmx.de> - 2011-10-18 08:42 +0200
Re: What role does "DOS" play in Windows 95/98? "Rod Pemberton" <do_not_have@noavailemail.cmm> - 2011-10-17 13:34 -0400
Re: What role does "DOS" play in Windows 95/98? DOS Guy <DOS@Guy.com> - 2011-10-17 16:43 -0400
Re: What role does "DOS" play in Windows 95/98? Ross Ridge <rridge@csclub.uwaterloo.ca> - 2011-10-17 18:34 -0400
Re: What role does "DOS" play in Windows 95/98? DOS Guy <DOS@Guy.com> - 2011-10-17 19:29 -0400
Re: What role does "DOS" play in Windows 95/98? Ross Ridge <rridge@csclub.uwaterloo.ca> - 2011-10-17 20:36 -0400
Re: What role does "DOS" play in Windows 95/98? DOS Guy <DOS@Guy.com> - 2011-10-17 21:36 -0400
Re: What role does "DOS" play in Windows 95/98? Ross Ridge <rridge@csclub.uwaterloo.ca> - 2011-10-18 09:46 -0400
Re: What role does "DOS" play in Windows 95/98? "Rod Pemberton" <do_not_have@noavailemail.cmm> - 2011-10-18 10:51 -0400
Re: What role does "DOS" play in Windows 95/98? Ross Ridge <rridge@csclub.uwaterloo.ca> - 2011-10-18 13:49 -0400
Re: What role does "DOS" play in Windows 95/98? Ross Ridge <rridge@csclub.uwaterloo.ca> - 2011-10-17 12:46 -0400
Re: What role does "DOS" play in Windows 95/98? DOS Guy <DOS@Guy.com> - 2011-10-17 19:46 -0400
Re: What role does "DOS" play in Windows 95/98? Trifle Menot <triflemenot@beewyz.com> - 2011-10-18 00:14 +0000
Re: What role does "DOS" play in Windows 95/98? Ross Ridge <rridge@csclub.uwaterloo.ca> - 2011-10-17 20:56 -0400
Re: What role does "DOS" play in Windows 95/98? "Klaus Meinhard" <K_Meinhard@gmx.de> - 2011-10-18 08:53 +0200
Re: What role does "DOS" play in Windows 95/98? DOS Guy <DOS@Guy.com> - 2011-10-18 09:12 -0400
Re: What role does "DOS" play in Windows 95/98? Jim Leonard <mobygamer@gmail.com> - 2011-10-18 07:03 -0700
Re: What role does "DOS" play in Windows 95/98? "Klaus Meinhard" <K_Meinhard@gmx.de> - 2011-10-19 10:07 +0200
Re: What role does "DOS" play in Windows 95/98? "Ant" <not@home.today> - 2011-10-19 01:26 +0100
Re: What role does "DOS" play in Windows 95/98? "Klaus Meinhard" <K_Meinhard@gmx.de> - 2011-10-19 09:19 +0200
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