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Tomorrow on 15th of July Microsoft is staring pre-order of Windows 7. I compared the three editions ("Which one is right for you?") for me. The main difference is "Windows XP Mode" in Professional and "switch between languages" in Ultimate.

I don't need to switch between languages (this means no Ultimate). So the main question "Why do I need Windows XP Mode in Windows 7?". Serious, what are the advantages of running Windows XP in a virtual machine under Windows 7? Do I really need that? Or is it only for people still using 10 year old applications which will never be upgraded to Windows 7? There is no sense to me.

Or do I also have the possibility to run a UNIX OS in the virtual machine of Windows 7, so I can also start UNIX applications on my Windows Desktop?

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Shouldn't the question title be something more like "Why do I need Windows XP Mode in Windows 7?" –  alastairs Jul 14 '09 at 12:59
    
To "alastairs": You are right, the correct title of this post should be "Why do I need Windows XP Mode in Windows 7?". –  Alexander Jul 14 '09 at 14:10
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migrated from serverfault.com Jul 30 '09 at 13:41

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7 Answers

The XP mode is precisely what you said it was - for people who use old applications (or games, as it may be) that for some reason or other cannot be replaced or upgraded.

Imagine an old accounting system which might still work, but have a rather costy upgrade that can't be justified to get past bookkeeping. Or where the developing company has died off, and since it is closed source, no-one can maintain it.

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Thanks for your answer! Home Premium (~70$) should be enought. There is no need for paying ~400$ for the Professional edition if a XP licence only costs 32$. –  Alexander Jul 14 '09 at 12:44
    
Windows 7 Pro is based at $299 for the full retail version (not an upgrade or OEM). We recently purchased the upgrade during the promotional period for $99 each. I expect you'll be able to find a similar deal when Windows 7 is close to release (or at least use the upgrade which should be $199). –  Russ Warren Jul 14 '09 at 14:30
    
As its running under Virtual PC the gaming argument is probably a bit weaker? –  svandragt Aug 6 '09 at 12:46
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A technical reason for "XP mode" is to support 16-bit code. On an x86 CPU running in 64-bit mode it is "expensive" (read: slow) to change the mode of the processor to allow 16-bit programs to execute properly. It's so bad that Microsoft didn't put in any infrastructure into any 64-bit versions of Windows to support 16-bit code.

"XP mode" runs a virtual 32-bit Windows XP instance, and the virtualiation environmnet handles the 16-bit / 64-bit transition. In effect, "XP mode" is the 16-bit support infrastructure that Microsoft never put into prior versions of 64-bit Windows, with the added bonus of having a full Windows XP 32-bit environment to suppot problem software that doesn't want to run in Windows 7.

Unless you've got software that uses either 32-bit kernel-mode drivers (or the aforementioned 16-bit code on 64-bit Windows) you'll very likely never have need for "XP mode". The VAST majority of 32-bit Windows software runs w/o any problem in the "compatibility modes" already provided in every edition of Windows 7.

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I had the same question. It became a really important feature for me as we're rolling out new computers with lots of RAM in them, and 32 bit just doesn't handle loads of RAM well. So then we had a problem with some applications and drivers not working on 64bit Vista (or '7). Online banking with smartcards was one application.

So the answer was to use Windows 7 RC Windows XP mode to allow Internet Explorer to 'bleed through' into the real OS, which works really nicely. This means IE appears as if it's on the local desktop (still one IE icon click) and it runs up the VM version of IE without any other interface clutter.

I'd grab the RC and take a look if I were you...

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The effect that the application seems to be running on the same desktop can also be achieved with VMware running in "Unity" mode. –  Alexander Jul 14 '09 at 20:54
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Internet Explorer 6. Many web-based, corporate applications require ActiveX Controls that only work on IE6 or websites that only work properly with IE6. I think this is actually irresponsible on the part of the vendors of these applications, but that's another discussion.

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Or do I also have the possibility to run a UNIX OS in the virtual machine of Windows 7, so I can also start UNIX applications on my Windows Desktop?

coLinux can do something like this.

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The XP mode is just a normal MS Virtual PC instance running a XP image. If you have a valid XP license there is nothing XP mode has to offer as you could just install Virtual PC make install XP yourself (or linux/unix).

Additionally to legacy application support it can also be used for old hardware without Vista/Win7 drivers (e.g. my current printer).

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You need it to make sure applications actually work on your new system. As always, there are poorly written applications whose developers didn't not bother to read docs, but instead just tested on XP. Well, one could easily blame Microsoft for this because they failed to release a new operating system for so many years that people forgot that any compatibility is needed anyway.

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