Leading analysts are making different predictions about the impact of Windows 7 on PC sales, and the reasons seem to boil down to the time frame considered, plus the perspective of the particular analyst.

"Windows 7, with its polished user interface and several new consumer-friendly features, will likely reduce the gap in perception between Windows and Mac OS," wrote Annette Jump, research director in Gartner's Worldwide (WW) Client Computing Team," in a blog on the Gartner site.

But on the other hand, "Gartner does not expect that Windows 7's release in October 2009 will have a major boost on WW PC sales in the fourth quarter of this year," according to Jump.

Quite conversely, Chris Whitmore, a hardware analyst for Deutsche Bank, wrote this week in a research note: "We expect Windows 7 to spark a multiyear upturn in PC unit growth."

Obviously, one of these analysts is saying "no," and the other "yes," on the question of whether Windows 7 will bring a leap in PC sales. Gartner's Jump, though, is talking about the fourth quarter of this year, whereas the Deutsche Bank analyst -- who was originally quoted in a WSJ article -- is referring to a multiyear time frame.

Whitmore, in fact, also appears to be thinking that a surge in sales won't come immediately after Windows 7's release. He goes on further in the research note to project that PC unit sales will pick up significantly a quarter or two after Microsoft has done new OS upgrades.

Speaking with me on the phone this afternoon, Steve Kleynhans, another Gartner analyst, got very specific about his own opinions on the question.

"The effect of Windows 7 is going to come in two waves," predicts Kleynhans, a research vice president at Gartner.

The first wave of Windows 7 sales will be driven by consumers, and the second one by business customers, according to the analyst.

Both sales waves will be in turn impacted by economic factors, and these still remain iffy.

"We'll see how Christmas does among the consumers," he says. Some households that want new Windows 7 PCs just won't have enough money at hand to do so this holiday season, he suggests.

The business market, on the other hand, isn't likely to see a boom in new PC sales until the end of 2010 or even the start of 2011, according to Kleynhans.

Although Windows 7 will play a key role, businesses will also be feeling a need to replace their PCs, something that many of them won't have done for two-and-a-half years. "So Windows 7 is nicely timed," Kleynhans told me.

But even then, the size of the sales boom will hinge on the state of recovery from the recession. Like consumers, businesses today don't tend to have "hidden piggy banks" that will allow them easily go out and buy new PCs, according to the Gartner analyst.

"Corporations might buy cheap PCs, and that isn't necessarily a good idea," he observes.