According to sources, the Cupertino, Calif., Mac maker has been working steadily on maintaining current, PC-compatible builds of its Unix-based OS. The project (code-named Marklar, a reference to the race of aliens on the "South Park" cartoons) has been ongoing inside Apple since the early days of its transition to the Unix-based Mac OS X in the late '90s.

Sources said more than a dozen software engineers are tasked to Marklar, and the company's mainstream Mac OS X team is regularly asked to modify code to address bugs that crop up when compiling the OS for x86. Build numbers keep pace with those of their pre-release PowerPC counterparts; for example, Apple is internally running a complete, x86-compatible version of Jaguar, a k a Mac OS X 10.2, which shipped last week.