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Back when I was running some old Virtual PC, I thought that it only emulates some basic processor, like pentium, common hardware, like cirrus logic or other gfx card, common serial port and so on. All that, so any, and I mean ANY guest could run on Virtual PC. Yesterday I tried to install Windows '98 (don't laugh, I need it for some testing) on a Hyper-V, that came with Win8Pro. Not only it doesn't want to install off CD, but from what I read on the internet, it will not run at all, even if you manage to convert physical disk to virtual. Microsoft says basically to just piss-off, but what the hell, if i have a x86 processor emulated, install should succeed, no?

Some more elaborate people on the forums I visited, say that they tried, and because '98 is not a "supported GUEST" operating system, it won't run and that's it.

My question is WHY Hyper-V needs a "supported guest"? I'm not talking about integration functions, I could even live without a mouse, and Win98 can too, so why?

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2 Answers 2

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A hypervisor like Hyper-V does not fully emulate a PC, it "simply" takes the instructions from the guest and translates them to operations on the host.

The difference is that the instruction from the guest can often be executed directly on the host, because both client and host share a similar architecture. So the instruction can be passed right through. With a full emulation, the emulator will parse the instruction and calculate the result (or perform the corresponding action) on its own.

Now, the guest could use instructions that the hypervisor does not know how to translate. Then the guest operating system would not be supported.

There are also applications that actually emulate a PC, like bochs. But you will find that those operate a lot slower than a hypervisor like Hyper-V, because they actually emulate an x86 CPU, a graphics adapter, etc.

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I understand, and will give bochs a try –  Kitet May 14 '13 at 10:23
    
Should bochs fail, I recently installed win98 on VMware. That is at least a known working fallback. –  Hennes May 14 '13 at 10:46
    
@Kitet: I would recommend giving VirtualBox a try. It supports Windows 98. –  Oliver Salzburg May 14 '13 at 10:59
    
I already downloaded it too :D although bochs already runs my '98, save one bluescreen during install. –  Kitet May 14 '13 at 14:33
    
Could you be more specific? What part of the x86 instruction set does Hyper-V not support? –  Harry Johnston May 29 '13 at 4:31

Here, "Supported" more or less means "Commercially supported," that is, Microsoft product support will assist you when using a "supported" guest operating system on Hyper-V, if you've purchased service contract with Microsoft, and MS dev crews will test and release patches against "supported" guest OSes.

Windows 98 is indeed "technically" supported (or to say, can run) on Hyper-V, but as it is "unsupported," MS will not provide assisstance when you meet with problems, nor will it test with Win98 when doing development, so Win98 might totally break in some future version of Hyper-V or with certain patch(es) installed.

Especially, there is no integration component avaliable for Win98.

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Yeah, i know what that all means, I'm asking why I can't install any OS I want, given my understanding of what virtual machine does, e.g. emulates basic hardware and such... –  Kitet May 14 '13 at 9:33
    
Nothing stops you –  soandos May 14 '13 at 9:51
    
Something stopped me. –  Kitet May 14 '13 at 10:22
    
@bsfmig - This answer isn't correct. Your concolusion of what "Supported" means is not correct. Oliver's answer is 100% correct. You clearly don't understand how Hyper-V works. –  Ramhound May 14 '13 at 11:10

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