Apple said today that customers had downloaded more than one million copies of Mac OS X Lion from the Mac App Store in the upgrade's first day of availability.
"In just one day, over one million users bought and downloaded Mac OS X Lion," Apple said.
Lion is priced at $29.99.
The phrase "bought and downloaded" could be interpreted in other ways, however.
Because Mac owners can download multiple copies of Lion -- Apple allows them to pay once, then install the OS on all their personal machines -- it's possible that first-day revenues were far less than $30 million.
Apple also said that Lion was selling "faster than any other OS release in [the company's] history."
A direct comparison to Lion's predecessor, Snow Leopard, is impossible: Apple did not release early sales figures for that operating system after its August 2009 debut.
In September 2009, retail research firm estimated that Snow Leopard sold twice as many copies in its first two weeks than its predecessor, 2007's Leopard, and almost quadruple the number posted by Tiger, which shipped in 2005.
Snow Leopard sold for $100 less than Leopard or Tiger, one reason why that edition flew off the shelves, NPD Group analyst Stephen Baker said two years ago.
In October 2007, Apple claimed that it had sold or delivered 2 million copies of Mac OS X 10.5 Leopard in the first fours days. But the Leopard number included copies installed on new Macs sold during that stretch.
Causes for Lion's faster sales pace could range from a larger number of Macs in use now than in 2009 -- Apple has sold 28.5 million Macs worldwide since Snow Leopard's launch -- to its online-only distribution, which doesn't require customers to drive to a physical store or wait for an online order to be delivered.
Apple plans to sell Lion on a USB flash drive for $69 next month, and the company also sells Lion Server for $49.99 as an add-on/upgrade to Lion.
Not surprisingly, Lion has held the top spot in the Mac App Store's bestseller list since it's launch early Wednesday. As of 6 p.m. ET, Lion Server was in the No. 3 position on the paid-app list.
By late Thursday, Lion had collected over 9,500 customer ratings, and boasted a collective score of 4.5 out of 5 stars.
Lion can be downloaded from the Mac App Store and installed on most Macs running Snow Leopard 10.6.6 and later.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer or subscribe to Gregg's RSS feed . His e-mail address is firstname.lastname@example.org.