Both of the analyst firms I use as the basis for my quarterly and annual PC sales data reports have issued preliminary findings for the fourth quarter of 2010, and for the year. And what both Gartner and IDC found is that PC sales grew strongly for the year, but not as fast as expected in the final quarter. Both also credited the rise of the iPad for the shortfall, although even the most optimistic iPad sales forecasts don't explain the difference.

Using averages of the company's figures, as always, we find that PC makers sold almost 350 million PCs in 2010—a 13.7 percent jump from the year before. Fourth-quarter PC sales were softer than expected, however, jumping just 4.3 percent to 92.8 million units.

Both firms say that while business PC sales grew steadily throughout 2010, consumer PC sales slowed slightly. And both raised the scary specter of Apple's iPad as the cause.

But was it?

Apple will release its actual unit sales figures later this month, but using the most optimistic estimates, Apple could have sold as many as 14 million iPads in 2010. That figure represents about 4 percent of all PC sales in the year. However, since the iPad was only available for three of the four quarters of 2010, a more accurate yearly figure would be approximately 5.5 percent (or about 19 million iPads).

So, did PC sales fall short by that amount in 2010, compared with the firms' initial predictions? Actually, no. The average of both firms' predictions for PC sales in 2010 was in fact 350 million PCs. The actual figure, using the same averaging, was 348.5 million. And let's remember that PC makers shipped about 300 million PCs a year before. This means approximately 50 million additional PCs were sold in 2010, the year the iPad was released. Just that growth figure is over twice as high as the estimated annual sales of the iPad, had it been available for the full year (48.5 million PCs vs. 19 million iPads).

More to the point, Gartner predicted that PC sales would grow 12 percent in 2010. But Gartner's final figure for the year was higher, at 13.8 percent. (Averaged growth between IDC and Gartner was 13.7 percent.)

So I'm down on the iPad, right?

Not exactly. There's no arguing that Apple has created a new market with this innovative new device. There's also no arguing that the iPad (and devices like it), through a steady series of software and hardware updates, will quickly rival the functionality of the PC, especially for mainstream users, and will challenge the PC as the mainstream computing device going forward.

The real impact of the iPad—and of its similar competitors—will start being felt in 2011. Part of the reason will be the expected improvements and new iPad models that Apple will introduce this year. Another factor is a steady stream of competition, including many based on Android 3, the HP Palm device, and Research in Motion's (RIM's) PlayBook. I suspect that when we look back on 2011, these tablet devices will have had a measurable impact on PC sales.

It just didn't happen in 2010, sorry.

One final point: You'll note that I didn't include any mention of tablets based on Microsoft's Windows 7 in that mix of competitive devices. The rationale here is simple and two-fold: First, Windows 7-based tablets are PCs and will be counted among PC sales. Second, such devices won't be competitive and will have a negligible or non-existent impact on overall PC sales for the year.

(I'll have more on these figures today on the SuperSite Blog, and then again when Apple releases its actual device unit sales, which often vary wildly from the IDC and Gartner estimates.)