That makes it the fastest launch of an Apple operating system ever, the company says. It released Mountain Lion Wednesday.
Apple charges $20 for the software. That pays for downloads for all of a buyer's personal computers.
Apple also provides the OS for free to buyers who bought a Mac on or after June 11.
Mountain Lion brings features from the iPhone and iPad to the Mac. The enhancements include tight integration with Apple's online storage service, iCloud, and a "Notification Center" that shows incoming mail, calendar reminders and other events.
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