"Golden master," or GM, is a label some developers apply to software that is ready, or nearly ready, for shipping. Rival Microsoft calls the same milestone "release to manufacturing," or RTM, designating that the code is suitable for computer makers to install on new machines.

The appearance on the Apple developer website of Mountain Lion's golden master was reported Monday afternoon by several Apple-centric blogs, including , and later confirmed by Computerworld.

Its debut means that the on-sale date for Mountain Lion is probably between two and three weeks away.

Last year, , then launched the operating system 19 days later on July 20. In 2009, the pause between OS X Snow Leopard's final version and its retail availability was somewhat shorter, 16 days.

The only official word from Apple thus far is that Mountain Lion will hit the Mac App Store, its sole distribution channel, this month. Based on the company's past practice, including last year's surprise announcement at an earnings call that Lion would launch the next day -- and with that quarterly call slated for July 24 this year -- Computerworld has pegged the .