PC users around the globe may find driver software is stopped from working by Vista if it detects unauthorised content access, claims a new report.

Peter Guttman, a security engineering researcher at New Zealand's university of Auckland, has written A Cost Analysis of Windows Vista Content Protection. He believes Vista is trying to achieve the impossible by protecting access to premium content. Users will find their PCs' compromised by the persistent and continuous content access checks carried out by Microsoft’s latest operating system (OS).

Guttman thinks these checks and the associated increase in multimedia card hardware costs make Vista's content protection specification “the longest suicide note in history”.

The core elements in Vista have been designed to protect access to premium content. The design requires changes in multimedia cards before Microsoft will support them for Vista use.

Content that is protected by digital rights management (DRM) must be sent across protected interfaces. This means cards using non-protected interfaces can't be used by Vista PCs.

The report also pointed to a number of features the stringent Vista content protection measures can disable and degrade on a PC.

Vista is disadvantaging high-end audio and video systems by openly disabling devices. The most common high-end audio output interface is Sony/Philips Digital Interface Format (S/PDIF), which doesn't have any content protection. It must be disabled in a Vista system when DRM-protected content is being played. Equally a high-end component video interface (YPbPr) also has no content protection and must be disabled when protected video is being played.

Vista covertly degrades playback quality. PC voice communications rely on automatic echo cancellation (AEC) in order to provide acceptable voice quality. This requires feeding back a sample of the audio mix into the echo cancellation subsystem, which isn't permitted by Vista's content protection scheme. This lowers PC voice communication quality because echo affects will still be present.

This overt and covert degrading of quality is dynamic, not consistent. Whenever any audio derived from premium content is played on a Vista PC, the disabling of output devices and downgrading of signal quality takes place. If the premium content then fades away the outputs are re-enabled and signal quality climbs back up. Such system behaviour today indicates a driver error. With Vista it will be normal behaviour.

Vista has another playback quality reduction measure. It requires that “any interface that provides high-quality output degrade the signal quality that passes through it if premium content is present. This is done through a "constrictor" that downgrades the signal to a much lower-quality one, then up-scales it again back to the original spec, but with a significant loss in quality”. If this happens with a medical imaging application, then artifacts introduced by the constrictor can 'cause mis-diagnoses and in extreme cases even become life-threatening.'

The report also highlighted Vista’s CPU cycle guzzling tendencies. The OS will use much more of a PC's CPU resource because “Vista's content protection requires that devices (hardware and software drivers) set so-called "tilt bits" if they detect anything unusual…Vista polls video devices on each video frame displayed in order to check that all of the grenade pins (tilt bits) are still as they should be”, slowing performance.

Also, “in order to prevent tampering with in-system communications, all communication flows have to be encrypted and/or authenticated. For example content sent to video devices has to be encrypted with AES-128”, where encryption/decryption is known to be CPU-intensive.

Device drivers in Vista are required to poll their underlying hardware every 30ms – thirty times a second – to ensure that everything appears correct.

It is apparent that Vista is going to use very much more of a PC's resources than previous versions of Windows and degrade multimedia playback quality unless the user has purchased premium content from a Microsoft-approved resource.

Such over-reaching by Microsoft could prove to be the catalyst needed to spur increased take-up of alternatives including Linux desktop operating software or Apple's Mac OS.