NEW YORK (CNN/Money) - Microsoft and several top-tier computer makers introduced the new "Tablet PC" with much fanfare Thursday, but it remains uncertain how popular the device will be.

Several PC makers, including Hewlett-Packard, Fujitsu and Acer, have been showing off their prototype Tablet PCs for more than two years.

A sort of cross between a laptop computer and a personal digital assistant, Tablet PCs are fully functioning Windows-based computers with touch screens and features that enable users to input and manipulate data using a stylus.

They run Microsoft's newest operating system software, called Windows XP Tablet PC edition, and come in a range of styles and sizes.

Some include attached keyboards that can be folded away when using the stylus for input but still provide the option to use the device as if it were a normal notebook computer. Others come in a so-called "slate" form, where all of the data is entered through the screen.

ViewSonic's ViewPad 1000 is one of several Tablet PC products that began shipping Thursday.

Microsoft -- whose chairman and founder, Bill Gates, recently predicted that the Tablet PC would become "the most popular personal computer sold in America" -- sponsored a marketing event in New York City Thursday during which it showcased Tablet PCs from nine different vendors.

The company also touted some new software that has been designed specifically to take advantage of the new platform.

Microsoft already invested roughly $400 million in development and research for the Tablet PC. The company is expected to spend tens of millions more marketing the new devices.

Even so, Tablet PCs, all of which carry price tags exceeding $2,000, are not expected to make a big mark on the industry in the near term.

"There is a tremendous price premium attached to buying these devices at a time when money is tight," said Leslie Fiering, an analyst at high-tech research firm Gartner Dataquest.

Initial interest could cause an early spike in purchasing that will eventually level out, Fiering said.

Gartner Dataquest expects a six- to nine-month evaluation period before any volume purchases are made. And most of those are likely to be by companies in industries that already use some sort of mobile data-entry devices, such as warehousing and shipping or medicine.

Next year, Gartner Dataquest expects 2003 Tablet PC shipments to reach 425,000 units, representing roughly 1.2 percent of mobile computer shipments. Looking further out, Gartner Dataquest expects as many as one-third of all mobile computers will make use of the Tablet PC platform.

"We're pretty bullish, but we believe it's going to take time," Fiering said.

Although some big name hardware makers have put their weight behind the Tablet PC, some notable others have decided to wait and see if the demand materializes before they try to build and market one.

Among them are IBM and Dell Computer, which have said they are uncertain whether there would be broad appeal for such products.

Roger Kay, a PC analyst at International Data Corp., noted that the Tablet PC concept came "entirely from the supply side," and was not put forward to satisfy an established consumer demand. His firm also is expecting very modest initial adoption rates.

"We expect one to two years of pretty low numbers until you get some real uptakes," Kay said. "But Microsoft is putting everything it's got behind this, so it could have a wider adoption than we think."