For the latter, customers who later want to upgrade to Windows 8 must pay for the upgrade. That's not the case with a PC purchased with Windows 8 Pro that has been downgraded to Windows 7 Professional (or Vista Business).
"At any time, you may replace an earlier version with Windows 8 Pro," read Microsoft's licensing agreement.
Do-it-yourself downgrades will be more complex with Windows 8, however, as users must first modify the PC's BIOS to boot into what's called "legacy mode." By default, Windows 8 will use UEFI-mode (Unified Extensible Firmware Interface) boot on new PCs to enable some new features, including Secure Boot.
Notebooks, desktops and other devices powered by Windows 8 Pro will go on sale Oct. 26.
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