The upgrade, the first since June 2007, includes nearly 60 new features and boasts significant performance improvements, said Rawee Kambhiranond, Parallels' senior product marketing manager. "We knew we had to improve on [Parallels'] performance," Kambhiranond said, "and we've pushed it to its limits."

One of the new version's performance enhancements that Kambhiranond touted was something Parallels has dubbed Adaptive Hypervisor, which better balances the processor load between native Mac OS X and any running virtual machines. It also gives the user more control over the number of processors devoted to the virtual machine, as well as the amount of allocated memory. "And if [the VM] doesn't use the memory, Parallels will load balance accordingly," Kambhiranond said, by returning the unused portion back to Mac OS X.

Parallels Desktop for Mac 4.0 can dedicate up to eight processor cores and as much as 8GB of physical memory to a virtual machine.

In all, Kambhiranond claimed that users should see a 50% performance boost by moving to Parallels Desktop for Mac 4.0 from the earlier edition.

Other additions to the upgrade include guest operating system support for Leopard Server and Windows Server 2008, as well as what Kambhiranond called "experimental" support for Snow Leopard Server. The virtualization software now also offers Mac gamers who play Windows titles support for DirectX 9.0, DirectX Pixel Shader 2.0 and OpenGL 2.0.

Interface changes to the program include the new Modality viewing mode that lets users change resolutions of virtual machines on the fly, and modifications to Coherence -- the Parallels feature that makes Windows applications appear to run directly on the Mac desktop -- that put Windows system tray notifications on the Mac OS X menu bar.

A new Safe Mode also lets users restore any virtual machine to its initial state, discarding all changes made during a session. Kambhiranond hinted that it could be used as an uber-privacy mode to, for instance, browse in a virtual machine. "No, I won't call it a 'porn mode, I'll let you do that," said Kambhiranond when asked if the term, which is often used to describe private-browsing features in Apple Inc.'s Safari and Google Inc.'s Chrome, fits Safe Mode.

Bundled with Desktop for Mac 4.0 are a Parallels-branded edition of Kaspersky Lab's Internet Security and Acronis True Image, a Windows-based backup and restore application, for backing up virtual machines to local or networked drives.