By Joseph Menn and Chris Nuttall

Hewlett-Packard has become the first computer manufacturer to release a tablet running Microsoft’s Windows 7 operating system, releasing a model aimed at US business users on Friday, more than six months after Apple’s iPad launch.

Microsoft’s Steve Ballmer brandished a prototype HP tablet at a technology conference in January, but the top computer company wavered after it bought smartphone maker Palm, which owns the webOS operating system.

In spite of concerns inside HP about the touch-screen functions of Windows 7, the company later committed to deliver both Friday’s Windows tablet and a webOS slate, which executives said will ship early next year.

While a relief to Microsoft, the debut of HP’s Slate 500 is coming with little of the fanfare that herald a significant challenger to the iPad.

The device is designed for companies wedded to Windows elsewhere, especially those that might want to install their own applications, HP said.

“Businesses really wanted to have something in common with the rest of their environment so they could have one [Windows] image to work with,” said Carol Hess-Nickels, HP’s director of business notebook marketing.

In delaying introduction in other countries, HP is forgoing even more of the audience claimed by Apple. That company has already sold close to 8m iPads, which were designed mainly for consumers but have been adopted by many businesses as well.

Other large manufacturers have so far shunned Windows 7. One Lenovo executive criticised it as being too optimised for the mouse-and-keyboard approach of a desktop PC.

Executives at US manufacturer Dell declined to promise a Windows-based tablet in interviews on Thursday, saying they were waiting to see progress from Microsoft.

Analysts expect Apple to dominate next year’s tablet market. The overall market could reach 50m units by 2013, Dell said.

HP’s $800 entry has an 8.9-inch screen, falling between the 9.7-inch iPad and 7-inch devices such as the Samsung Galaxy Tab, due out next month and running Google’s Android operating system.

In the business market, it will compete with the iPad, Cisco’s forthcoming Android-based Cius, and Research in Motion’s announced PlayBook, which runs RIM’s own QNX operating system.

HP executives said the introduction of a tablet for business using Windows this year did not necessarily mean HP would use Windows just for enterprise tablets and webOS just for consumer media tablets. It plans to use webOS on a variety of devices.