SAN FRANCISCO (AFP) - Apple released a preview version of its new Macintosh operating system on Thursday, bringing some features of the iPad to the personal computer.

The Cupertino, California-based company said the updated operating system, called Mountain Lion, will be available to Macintosh developers immediately and Mac owners can upgrade to the new software in late summer.

Apple said Mountain Lion includes a new Messages application which replaces iChat and allows a user to send unlimited messages, photos and video from a Mac to another Mac or a device running iOS software such as the iPad or iPhone.

It also includes integration with Twitter allowing users to sign in and tweet directly from Safari, Photo Booth and third-party applications.

Game Center allows for live multiplayer games to be played across iPhone, iPad or iPod Touch devices while with AirPlay Mirroring, a Mac user can wirelessly send video from a Mac to an HDTV using Apple TV.

Mountain Lion is the first Mac operating system built with the Internet "cloud" in mind, Apple said.

"More than 100 million users have iCloud accounts, and Mountain Lion makes it easier than ever to set up iCloud and access documents across your devices,"

it said.

Mountain Lion entices users into iCloud, which Apple chief executive Tim Cook this week described as one of the "profound changes" people will one day talk about with their grandchildren.

"If you dial back 10 to 12 years, Steve (Jobs) announced a strategy for Apple that positions the Mac or PC at the hub of everyone's life," Cook said Tuesday at a Goldman Sachs technology conference in San Francisco.

"iCloud turns that on its head," he said. "It recognizes that, across that decade, you and I live off multiple devices."

A new security feature called Gatekeeper protects Macs against malicious software by giving users control over what applications can be installed and downloaded, Apple said.

Cook, in an interview with The Wall Street Journal, said the new Macintosh operating system takes advantage of features popular on the iPad and iPhone.

"We see that people are in love with a lot of apps and functionality here,"

Cook said of the iPhone. "Anywhere where that makes sense, we are going to move that over to Mac."

Apple sold a record 5.2 million Macs last quarter.

In a nod to the booming China market, Mountain Lion boasts features tailored for Chinese users, giving them the option of using Baidu search in the Safari browser or uploading video directly to China websites Youku or Tudou.

Sales of Macintosh computers in China more than doubled last year, Cook said. "Not on a big base, but 100 percent is still good," he said. "China is a big focus for us."

Macintosh computers have benefited from a "halo effect" that started with the success of culture-changing iPod players introduced in 2001 and which has continued with iPhones and iPads, according to Cook.

"The world changed for us in many ways when the iPhone launched," Cook said, explaining that the hit smartphones brought the California company to the attention of millions of people around the world who "had never met Apple."

"You can definitely see a synergistic effect of these products," he said.

The iPad is eating into desktop computer sales in what late Apple co-founder Steve Jobs branded the "post-PC era" but is taking a bigger bite out of sales of machines powered by Microsoft's Windows software, according to Cook.

"I do believe the iPad is cannibalizing some Mac, but it is cannibalizing more Windows PC," Cook said at the conference.

"The way we see cannibalization is we prefer to do it rather than have somebody else do it," he said. "It doesn't mean the PC is going to die; I think the Mac can still grow."