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(Pocket-lint) - It’s bad news for some Mac users as it’s confirmed Apple’s new Mountain Lion operating system won’t be compatible with older versions. 

Apple has listed which Macs are available for upgrade on its official Mountain Lion upgrade page. Though the manufacturer hasn’t gone into detail on the reason why some will be omitted from the upgrade, it appears it’s due to some Macs having an inferior graphics driver.

For a Mac to run Mountain Lion it appears you’ll need a 64-bit kernel. However, older Macs that use a 32-bit kernel extension (KEXTs) to make up the difference won’t work cleanly enough for Apple to give the green light.

Rather than invest resources in updating these older graphics drivers, Apple is concentrating on more recent models, though if you’ve got an iMac or MacBook Pro from as early as mid 2007 then you’re in luck because you’ll still be able to upgrade. 

Mountain Lion is due to be rolled out before the end of July for $19.99 from the Mac App Store, though developers have already got their hands on a Golden Master version of the OS.

For a full list of what Macs are compatible with Mountain OS click here.

Is your Mac compatible with Mountain Lion? If not, what are your thoughts. Let us know in the comments below.

Writing by Danny Brogan.