With Windows 8, Microsoft is allowing owners of previous Windows versions to upgrade from a previous version of Windows in a variety of ways. In the old days, we thought of this process as a clean install, in-place upgrade, or migration, depending on the method used. But with Windows 8, things are a bit more nuanced. Here’s what’s changing.

There are basically two ways to install Windows 8. You can boot your PC with some type of boot media—a DVD Setup disc, perhaps, or a USB-based Setup drive, for most individuals—or you can run Setup from within a previously-installed Windows version and go from there.

If you choose the former install type, not much has changed from Windows 7. Eventually, you’ll hit the Setup screen depicted below, which will ask you to choose between two options, Upgrade and Custom.

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It’s the latter case where things have changed fairly dramatically in Windows 8. And while you can simply run Setup from within a previously-installed Windows version using some form of Setup media, this new OS also offers a new web-based installer option which I’ve found to be superior. That’s because the web-based installer offers additional capabilities, including functionality that Microsoft used to offer separately in its Upgrade Advisor and Windows Easy Transfer utilities.

More to the point of this article, when you run Setup from a previous Windows OS, either with Setup media or from the web, what you see with regard to upgrade capabilities will differ depending on which OS version you’re coming from. And that’s where the nuance bit comes in. With Windows 8, Microsoft is somewhat blurring the lines between clean installs, in-place upgrades, and migrations.

This change manifests itself in the following screen in Setup, called “Choose what  to keep”:

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You’re given up to three choices, and what you see will again depend on which OS you’re coming from. These choices can include:

Windows settings, personal files, and apps. Previously called an in-place upgrade, this install type will carry over virtually everything from your existing Windows installation, including traditional desktop applications, as the OS is upgraded to Windows 8. This is the most complete install type because nothing will be lost.

Just personal files. This install type, previously called a migration, will save everything in your personal folders (all of your documents, desktop files, and so on, as well as those for any other user accounts), wipe out Windows and perform a clean install, and then copy the personal files back. What you lose with this type of install are your custom settings and your applications, which will need to be reinstalled.

Nothing. This is what we used to call a clean install, or what Microsoft calls a custom install. In this install type, Setup will wipe out all of the files and data on the disk and then install a factory-fresh version of Windows. Everything that was there will be lost, including your applications, your custom settings, and your documents and data.

The question, of course, is which of these options you’ll see. And thanks to a recent blog post by Mary Jo Foley, Microsoft details its Windows 8 upgrade plans, we know how the following Windows versions will react when confronted with the web-based Windows 8 Setup:

Windows 7 Starter, Home Basic, and Home Premium can support an in-place upgrade (where Windows settings, personal files, and applications are kept from the previous OS) to Windows 8 Core.

Windows 7 Starter, Home Basic, Home Premium, Professional and Ultimate can support an in-place upgrade (where Windows settings, personal files, and applications are kept from the previous OS) to Windows 8 Pro.

Windows 7 Professional and Enterprise can support an in-place upgrade (where Windows settings, personal files, and applications are kept from the previous OS) to Windows 8 Enterprise.

Windows Vista (RTM) can support a migration (where just personal files are kept from the previous OS) to Windows 8 Core or Pro.

Windows Vista with Service Pack 1 can support a migration (where personal files and system settings are kept from the previous OS) to Windows 8 Core or Pro.

Windows XP with Service Pack 3 can support a migration (where just personal files are kept from the previous OS) to Windows 8 Core or Pro.

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A couple of caveats apply here:

Cross-architecture upgrades. If you’re running a 32-bit version of Windows, you can only upgrade to a 32-bit version of Windows 8. Ditto for 64-bit versions; you can’t go from a 32-bit version of Windows to a 64-bit version of Windows 8 or vice versa.

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Cross-language upgrades.  If you are performing a cross-language upgrade using Windows Vista or 7, your only option is a migration (where only personal data files are kept).

For the most part, of course, this is all common sense, and it’s pretty admirable and even surprising that Microsoft supports the level of upgrading it does with Windows 8.