Microsoft disclosed at TechEd 2006 in Sydney Thursday that 32-bit versions of Windows Vista would never support high-definition protected content, including HD DVD and Blu-ray movies. The new formats will require 64-bit systems running the x64 edition of Vista.

The news, first reported by Australian tech publication APC Magazine, may come as a surprise to many Windows users looking to take advantage of the high-definition support with their current hardware. For example, Intel's Core Solo and Core Duo chips -- included in many laptops -- are not 64-bit compatible.

x64 editions of Windows require drivers that are signed by Microsoft, which means they have undergone extensive testing. The process is costly for manufacturers, and even common hardware devices such as wireless network cards still lack proper drivers. In turn, few manufacturers ship PCs running the 64-bit operating system.

Microsoft says it had to leave unsigned driver support in 32-bit versions of Vista due to application compatibility problems. Consumers would encounter the same errors and non-working hardware with Vista as they do on x64 editions now if the change was made.

This issue is the core reasoning behind Microsoft disabling the high-definition playback functionality. 32-bit versions of Windows allow unsigned code to be run in kernel mode, which means a piece of software could effectively bypass any copy protection on the discs.

Media companies pushed Microsoft on the matter and asked the Redmond company not to enable playback on 32-bit Windows, said senior program manager Steve Riley during a TechEd session. Riley added that the disc formats themselves would work fine, and only commercially produced movies would fail to play.