Windows XP Mode for Windows 7 (Part 1)

If you would like to read the next part of this article series please go to Windows XP Mode for Windows 7 (Part 2).


Most people think of Windows 7’s Windows XP Mode solely as a backward compatibility mechanism. In this article I will explain why this feature has the potential to change the way that Microsoft designs all future Windows operating systems.

By now I have no doubt that you are all aware of the hype surrounding Windows XP Mode for Windows 7. What you might not realize though is that Windows XP Mode is much, much more than just a backward compatibility solution. This technology has major implications that dramatically alter all future versions of the Windows franchise. In this article, I will tell you why I believe this to be the case.

Why Windows XP Mode Got a Bad Name

When it was first announced (or leaked) that Windows 7 was going to contain Windows XP mode for backward compatibility, most of the posts on the Internet made it sound as though Windows 7 was going to ship with a fully licensed copy of Windows XP running inside of a virtual machine.

I have to tell you that I was less than impressed with such posts. After all, you can use Virtual PC 2007 to run Windows XP inside a virtual machine with Vista. Even if Microsoft threw in a Windows XP license, most of the people who this sort of feature would appeal to already have Windows XP licenses. As such, I wrongfully assumed that the Windows XP Mode feature was a marketing gimmick designed to convince the public that Windows 7 was not going to be plagued by the same types of compatibility problems that Vista has come to be known for.

Setting the Myths Straight

The myths that I cited in the section above are full of half truths. I want to start out by setting the record straight, and then I will go on to explain why Windows XP Mode is so important.

You have probably heard that Windows XP Mode is going to be based on Virtual PC technology. That part is true. Unfortunately, Virtual PC has gotten a bad rap for being slow and inefficient because early versions of virtual PC had to pass all of the guest machine’s hardware calls through the host operating system. However, Virtual PC 2007 has always supported hardware assisted virtualization, as shown in Figure A.

Figure A: Virtual PC 2007 supports hardware assisted virtualization

Virtual PC 2007’s hardware assisted virtualization is not a Hyper-V based hypervisor, but guest machines do run a whole lot faster when you enable hardware based virtualization. Keep in mind though, that Windows 7 is going to use Virtual PC code that has been updated. This code is not based on Hyper-V either, but I would not be a bit surprised to see Hyper-V become the standard in Windows 8.

The next myth that I want to set straight is that Windows 7 will offer Windows XP mode right out of the box. If you want to enable Windows XP mode, then you are going to have to download an add-on. This add-on, which is going to be considered an out of band update, will be freely available to anyone who has Windows 7 Professional, Enterprise, or Ultimate edition. If you would like to try Windows XP Mode today, you can download the current beta version here.

OK, now for the really important part… When you need to run an application in Windows XP mode, those applications are not going to be limited to running inside a virtual machine. Well, actually they will be running in a virtual machine, but you would not have to be confined to using the virtual machine’s GUI to run your applications. You can install an application in a Windows environment, but run that application through the Windows 7 interface alongside your other applications.

Why is This Such a Big Deal?

Obviously it is convenient to be able to run your legacy applications alongside your newer applications, but in the end you may be wondering why I said that I think that Windows XP mode will have major implications that could alter the future of the entire Windows franchise.

In order to understand why I say this, you need to have a bit of historical prospective. Windows 95 was Microsoft’s first major 32-bit version of Windows (actually Windows for workgroups 3.11 was the first, but I don’t consider that to be a major release). At any rate, Windows 95 was designed to natively run 32-bit applications, but at the time there were still a lot of people running 16-bit applications that were designed to run on Windows 3.1. In order to facilitate the use of these legacy applications, Microsoft developed a 16-bit mutex for Windows 95. The way that the architecture was implemented kept 16-bit code separate from 32-bit code, and there was even a separate multitasking engine for 16-bit applications. When it came to multitasking, all of the 16-bit applications were collectively treated with the same priority as a single, 32-bit application.

Today we have the same kind of thing going on with modern versions of Windows. 64-bit versions of Windows XP and Vista can run some types of 32-bit code, but this code must be kept separate from the 64-bit code.

So what does all of this have to do with Windows XP Mode? Well, Windows XP Mode is a first generation feature, so all it really allows us to do is to run a Windows XP based virtual machine. However, it also allows the Windows operating system to be greatly simplified.

Can you imagine how bloated and how prone to errors Windows 7 would be if Microsoft tried to make it natively fully backward compatible with Windows XP, but without using virtualization technology? I think that it is safe to say that Windows 7 would end up being a lot slower and less reliable than Vista.

By implementing Windows XP mode in the way that they have, Microsoft was able to design Windows 7 without having to build in special backward compatibility mechanisms.

To be fair, you are not going to see anything ground breaking in Windows 7. As we all know, Windows 7 was built on top of the Vista kernel. Having said that though, I believe Windows 7 is an extremely important architectural stepping stone for Microsoft. I think that Windows 8 will be a much lighter weight and efficient operating system. I also think that Microsoft will offer virtualization based plug-ins for backward compatibility.

In other words, I would expect Windows 8 to run only 64-bit code with absolutely no native support for 32-bit code. Those who need to run 32-bit code may be able to download a plug in that would allow them to do so, while the rest of us don’t have to worry about it. The same might be said for operating system compatibility. If someone needs to run applications that were designed for Windows XP, they might be able to download a Windows XP plug in.

Of course this is all speculation on my part, but Microsoft has laid the groundwork, and what I have described seems like the next logical step. Microsoft offers a product called Application Virtualization, which was previously known as SoftGrid. This product is designed to allow otherwise incompatible applications to be able to run side by side. Although Application Virtualization is an enterprise product, there is nothing stopping Microsoft from implementing similar functionality at the operating system level. Rather than using self contained virtualization for each individual application, Microsoft could offer virtualization modules that allow applications to run in the operating system for which they were originally designed.


So far I have told you what Windows XP Mode is going to be, and I have explained why I think that this is such an important development. There is a lot more that I want to tell you though. In Part 2 I will show you some of the cool new features that are going to be available to you as a part of the virtualization engine that Windows XP Mode is going to use.

If you would like to read the next part of this article series please go to Windows XP Mode for Windows 7 (Part 2).

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