Two interesting pieces of news this week provide a better sense for how 2012 will shake out for the PC market and Microsoft’s Windows 8 — but the long-term direction of the computing market remains very much up in the air.

Bloomberg News reports that Microsoft is on track to finish the new operating system this summer, with new Windows 8 PCs and tablets hitting the market around October. Not a huge surprise, by any means, but a good fact to nail down.

Meanwhile, the IDC research firm has updated its PC shipment forecast for 2012 and beyond, noting that “the launch of Windows 8 and the excitement generated by ultrabooks and other ultra-thin notebooks should drive second half sales in a much stronger way.”

But pretty much anything would be stronger than the meager 1.8 percent growth in the PC market last year, as supply chain problems and the continued rise of the iPad cut into sales of personal computers. For the current year, IDC’s numbers suggest a growth rate around 5 percent — not exactly setting the world on fire.

IDC’s projections show single-digit growth in the PC market through 2016.

“2012 and 2013 will bring significant challenges for Microsoft and the PC community,” says IDC’s Jay Chou in a news release. “The Wintel platform must evolve to accommodate user expectations of ubiquitous computing on a multitude of devices and physical settings. Windows 8 and ultrabooks are a definitive step in the right direction to recapturing the relevance of the PC, but its promise of meshing a tablet experience in a PC body will likely entail a period of trial and error, thus the market will likely see modest growth in the near term.”

Microsoft’s bet with Windows 8 is that it will be able to grab a larger piece of the tablet market (and possibly e-reader market, as well) through the new Windows 8 Metro interface, designed to work across tablets and traditional computers.

IDC’s traditional PC forecast at the top of this post doesn’t include tablet shipments, but the firm recently projected those numbers separately — predicting that tablets will be ruled by Android tablets and the iPad through 2016. (I’ve combined the PC and tablet shipment forecasts in the second chart above.)

The big wild card in my mind is the portable (aka notebook) segment of the PC projections, which IDC expects to drive much of the growth in the PC market over the next four years.

I’m not convinced it will play out precisely as IDC projects. Tablets could very easily take a larger chunk than the firm’s numbers show. In short, the portable computing segment is up for grabs. And if consumer preferences lean toward tablets over notebooks, Microsoft will be an underdog playing an away game.

Much of it will hinge on how Windows 8 is received.

Here’s hoping they’re adding those navigational cues for new users.

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