When purchasing Windows 7, you can choose either an upgrade version or full version. Both upgrade and full versions include the same features. Upgrade versions require that Windows XP or Windows Vista are installed on your computer before installing Windows 7. Full versions don't require a previous version of Windows to be installed on your computer.

An upgrade installation replaces your current version of Windows with Windows 7 and your files, settings, and programs are kept in place on your PC. You can perform an upgrade installation using either the upgrade or full version of Windows 7.

A custom installation replaces your current version of Windows with Windows 7 but doesn't preserve your files, settings, and programs (it's often referred to as a clean installation for this reason). For installation instructions, see Upgrading from Windows Vista to Windows 7 (custom installation). You can perform a custom installation using either the upgrade or full version of Windows 7.

You can purchase Windows 7 at retail locations or online. If you have a netbook or other PC that doesn't have a DVD drive, you can purchase and download Windows 7 online at the Microsoft Store.

Yes, you can buy the upgrade version of Windows 7, but you'll need to perform a custom installation. This means that you should back up all of your files to an external location and gather the installation discs or setup files for programs that you want to use with Windows 7. For detailed instructions, see Upgrading from Windows XP to Windows 7.

Yes, you can buy the upgrade version of Windows 7. In some cases you can upgrade directly to Windows 7, but in other cases you'll need to perform a custom installation.

If you're running Windows Vista, you can choose the Upgrade option if you're installing a corresponding or higher edition of Windows 7. The following table shows which editions of Windows Vista can be directly upgraded to Windows 7:

Windows 7 upgrade media was designed to be used on a computer that has Windows XP or Windows Vista installed on it. You can use upgrade media to install Windows 7 on a computer that doesn't have Windows XP, Windows Vista, or any version of Windows installed on it by starting (or booting) your computer from the Windows 7 DVD and performing a custom installation. However, you won't be able to activate Windows 7, which validates that you have a genuine copy of Windows and allows you access to all the features. For more information about activation errors, see Windows 7 activation error: invalid product key and Windows 7 activation error: 0xC004F061.

We recommend that you install Windows XP or Windows Vista before installing Windows 7 using upgrade media. Before you attempt to install Windows 7 using upgrade media on a computer that doesn't have Windows on it, see Installing and reinstalling Windows 7.

If you purchase the full version of Windows 7, you can format your hard drive, and then install Windows 7. If you purchase the upgrade version of Windows 7 and want to format your hard drive, you'll need to start (or boot) your computer from the Windows 7 DVD, and then perform a custom installation. You can click Drive options (advanced), and then format your hard drive. Don't use a program from another software manufacturer to format your hard drive before installing Windows 7. If you are using upgrade media and format the drive before starting the installation process, you won't be able to use the upgrade product key to activate Windows 7. For more information, see Installing and reinstalling Windows 7.