Windows XP quietly turned 10 years old this week, a milestone for the still-popular operating system that powers nearly half the world's PCs. Microsoft did not celebrate the anniversary, eschewing any congratulatory blog post or press release.

On August 24, 2001, Microsoft shifted Windows XP's status to RTM, for "release to manufacturing," a term it uses to mark the end of development and the move to duplication and release to computer makers. XP reached retail in October 2001.

Service Pack 2

One analyst questioned whether it was really the right anniversary to celebrate. "The Windows XP that people loved wasn't [the original 2001] XP, it was XP SP2," said Michael Cherry, an analyst with Directions on Microsoft, a research firm that covers only Microsoft.

Windows XP SP2, or "Service Pack 2," shipped three years later, in August 2004.

That edition, which Microsoft itself acknowledged was out of the ordinary for one of its service packs, added new functionality and dramatically boosted XP's security. Among the security-oriented changes were a revamped firewall that was switched on by default, a new Security Center that monitored bundled and third-party firewall and antivirus defences, and the introduction of DEP, or "data execution prevention," Microsoft's first anti-exploit technology.

"Windows XP is old," said Cherry. "Ten years in this business is a lifetime."

That's exactly what Microsoft has been saying of late.

Time to move on

Last month, Microsoft told customers it was "time to move on" from XP, noting that it had less than three years left in its support lifespan. Even earlier this year, executives on the Internet Explorer (IE) team called XP the "lowest common denominator" as they explained why the OS wouldn't run the new IE9, or any future browsers.

Cherry concurred, more or less. "I've been telling [clients] to move to Windows 7," he said, adding that the newer operating system, which Microsoft launched in October 2009, was suitably stable to replace the long running XP.

Windows 7 is the safe bet, said Cherry, even though Windows 8 is looming. If Windows 8 is solid, then moving to it from Windows 7 rather than from the aged XP will be a relative breeze, given that Microsoft has assured customers that any PC able to run 7 will also handle 8.

Cherry has expressed concern about Windows 8 before, and repeated those worries today.

"It looks like they're changing a lot in Windows 8," he said, pointing to the hints that Microsoft gave earlier this summer as well as the information it's been disclosing on the "Building Windows 8" for the last week.

To Cherry, a large number of changes in Windows 8 increases the chance that something may go wrong, either during development or after it ships, repeating the debacle of Vista when many customers complained about device driver compatibility.

According to metrics firm Net Applications, Windows 7 has been accumulating usage share at the expense of XP and Vista. At the end of July, Windows 7 accounted for 29.7% of all operating systems, while XP had a 49.8% share, the first time it had dropped under the 50% bar.

Microsoft plans to support Windows XP, specifically SP3, until April 2014.