As anticipated, Microsoft last Thursday granted a partial pardon to its long-running Windows XP operating system, which had been slated for a forced retirement from new sales starting this year.

But while the news was trumpeted by some as a general reprieve in part because of users clamoring to keep the six-year-old OS instead of having to migrate to Windows Vista that's not exactly the story. So what did Microsoft say? And how much has its plans for XP really changed?

Questions worth asking are usually worth answering, of course. Here are some of each on Microsoft's latest XP move.

What exactly did Microsoft do? The software vendor said it will let some computer makers continue preinstalling Windows XP Home on systems until June 30, 2010, or until a year after Microsoft rolls out the next version of its operating system, dubbed Windows 7 whichever of those dates comes first.

But the extension only applies to a specific category of mobile hardware, which Microsoft has given its own acronym: ULCPC (short for "ultra-low-cost PC"). That generally applies to the under US$400, sub-two-pound notebooks and laptops currently characterized by Intel's Classmate and Asustek Computer's Eee. These systems, which are expected to play a major role in the PC markets in countries such as India and China, were originally designed to run only Linux, the open-source operating system.

Microsoft yesterday maintained that it made the move not to stymie the growth of Linux but because users and hardware vendors alike are demanding XP on the ULCPCs. "One thing we've heard loud and clear, from both our customers and our partners, is the desire for Windows on this new class of devices," said Michael Dix, general manager of Windows client product management, in a canned Q&A posted on Microsoft's Web site. "We are enthusiastic about this category because it enables us to bring the benefits of Windows to more customers."

Does Windows XP Professional get the same extension? No. The business version of XP, which includes remote access tools, significantly beefed-up network support and much more sophisticated file and folder access controls than the home edition does, still goes away on the dates Microsoft has already set for ending sales.

So Microsoft didn't give XP a blanket extension? Absolutely not. Dix made it clear that the OS isn't getting a general reprieve. "There is no plan to extend sales of other editions of Windows XP beyond June 30, 2008," he said before launching into a recitation of what Microsoft sees as Vista's success in the market.

When will the other versions of XP officially be retired, then? There are several dates that apply, but the one you're probably thinking of is the June 30 deadline that Dix referred to. That's the last day when large computer makers -- the Dells and HPs and Lenovos of the world -- will be allowed to preinstall Windows XP on new PCs. It also marks the official end of XP as a retail product.

So-called "system builders" -- the small shops that assemble machines for customers -- can put XP on the PCs they sell until January 31, 2009. Microsoft pushed back the cut-off dates last September, when it postponed the then-looming demise of XP by five months.

Will other computer makers jump into the ULCPC market Microsoft certainly thinks so. To guide hardware OEMs in designing XP-capable ULCPCs, Microsoft yesterday issued a detailed set of guidelines (download PDF) for laptops that rely on flash-based storage instead of traditional hard drives.

It's dense reading in spots, if only because of the formulas that Microsoft says PC makers should use to determine such things as the amount of flash RAM to stick in the devices -- Flash Storage Capacity = WINXP_SIZE + APPS_SIZE + USER_DATA is an example. But in general, the guidelines spell out notebook PCs that pack 2GB to 8GB of flash storage and sport a minimum of 256MB of system memory and a processor running at 500MHz or faster.