Unlike the previously released Windows RT tablet, the Surface Pro is based on an x86 processor and can run legacy Windows applications. Given this capability, the company is hoping that its relatively high starting price of $900 will be considered reasonable, since it essentially marries a laptop with a tablet. By comparison, the 64 GB MacBook Air laptop is about $1,000, and the iPad 2 starts at $400.

The Surface Pro's release comes months after the formal unveiling in October of Windows 8, whose market acceptance has been slow. Last week, for instance, industry research firm Net Applications reported that Windows 8 had obtained only a 2.3 percent market share of desktop operating systems, compared with a 7.7 percent share for Windows 7 in its first three months.

'A Tweener'

Because of the slow start to the rollout of Win 8 and the mediocre-to-poor reception for the ARM-processor-based RT tablet, the Surface Pro is taking on a particularly important role in Microsoft's efforts to increase the platform's momentum and to give the company a better presence in tablets.

Initial reviews of the Surface Pro have praised its power, its ability to act as a PC and as a tablet, the HD screen, the quick start-up time, the metal kickstand, the touchscreen Windows 8 interface, and an optional snap-on cover that also serves as keyboard. The cover/keyboard is about $120 extra.

But the negatives have included a meager battery life of 4.5 to 5 hours, the pricing, its 2-pound weight, and some have complained about fan noise that occurs on occasion.

Leading computer reviewer Walt Mossberg of The Wall Street Journal, for instance, has called the Pro "too hefty and costly and power-hungry," and added that it's "something of a tweener -- a compromised tablet and a compromised laptop."

'Thin, Touch-Screen Ultrabook'

Ross Rubin, principal analyst at Reticle Research, noted that Microsoft CEO Steve Ballmer pointed to the Pro as the "more significant" member of the company's new tablet family. Rubin added that, without the ability to run legacy apps , the RT's "dearth of apps" put it at the same starting point as any new tablet trying to jumpstart an ecosystem, such as the PlayBook from Research In Motion (now called BlackBerry) or Hewlett-Packard's TouchPad.

Rubin said the hundreds of thousands of Windows 8 applications will help to make up for "the relatively few optimized apps" that are designed for the Pro tablet's form factor -- although one of the tradeoffs for the tablet being essentially a Windows laptop is the shortened battery life.

He told us the pricing "can be justified" as reasonable for a "very thin, touch-screen Ultrabook." The strongest argument Microsoft has for the Surface Pro, he said, is that "it is a best-of-both-worlds solution."