PC programmers have spent two decades developing bad habits along with their clever applications. The PC's first decade gave developers direct access to hardware, a difficult habit to break; the second decade gave them nearly as free a rein with a better-managed but still single-user machine, on which the user almost always had administrator powers.

At Microsoft's Los Angeles developer conference in September 2005, Microsoft engineer Robert Villahermosa showed a series of charts with the memorable title "Top Five Ways to Ensure Your Application Will Be Incompatible." The specifics of his warnings included respecting the Windows registry—applications must no longer treat it as a "private playground," Villahermosa said—and respecting the operating system's role in maintaining knowledge and control of system configuration.

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Developers must learn, for example, Vista's new conventions for interrogating hardware to avoid confusing the parameters of a virtual machine with the real machinery behind it.

Click here to read eWEEK Labs' review of Vista.

Villahermosa also warned against any hard-coding of file or directory locations, and against the placement of application data in the directory that contains the application's executable code.

In addition, Vista applications must anticipate their possible use on machines with multiple users who maintain different application customization settings and separate histories of state. This also applies to applications running on Windows XP, but developers have been able to get away with being casual about this practice because most XP systems have been running with administrator privileges all the time. User expectations for good behavior will rise as Vista shifts the center of mass from administrator accounts to standard user accounts.

Learning to live within those limits seems likely to be the submerged nine-tenths of the iceberg of potential compatibility issues with Vista. eWEEK Labs has watched a family spend the last year in an XP environment under a discipline of user accounts for everyone, including Dad, except when installing applications or performing software updates. The resulting catalog of failure modes has been long and astonishing, including such weirdness as refusing to display correct application-specific fonts unless administrator powers were provided.

Readers of eWEEK have also reported to us such outrageous episodes as applications that merely print courier service mailing labels but that "absolutely, positively" won't run except in an administrator account. In the Vista regime, that absolutely, positively will not do.

Technology Editor Peter Coffee can be reached at peter_coffee@ziffdavis.com.

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