Apple’s new Snow Leopard operating system has hit the ground running, according to research data released Thursday.

Sales during the first two weeks of Snow Leopard’s release “far exceed those of the last two Apple operating systems,” market research company NPD said. The group tracks U.S. retail sales. Snow Leopard launched Aug. 28, available as an upgrade at an affordable price of $29.

According to NPD, Snow Leopard sales were more than two times higher than those for the initial release of Leopard back in 2007, and almost four times higher than the Tiger OS in 2005.

“Even though some considered Snow Leopard to be less feature-focused than the releases of Leopard or Tiger, the ease of upgrading to Snow Leopard and the affordable pricing made it a win-win for Apple computer owners - thus helping to push sales to record numbers” NPD’s Stephen Baker said in a statement.

Apple is the No. 4 PC maker in the U.S., according to research group Gartner, with 8.7 percent of that market.

Arch foe Microsoft’s new Windows 7 operating system goes on sale October 22. It starts at $119.99.

Retail sales