While Microsoft has regularly touted the improvements in Internet Explorer 10 on Windows 8, the company has said next to nothing about the browser and Windows 7, the operating system that powers 44% of all Windows PCs.

Last year, when Microsoft first introduced Internet Explorer 10 (IE10), it promised that the new browser would run on not only the new Windows 8's desktop mode, but also on 2009's Windows 7.

Even though the company has updated the previews of IE10 for Windows 8 six times, most recently May 31 when it shipped Windows 8 Release Preview, it stopped serving sneak peeks for Windows 7 more than a year ago.

The last preview capable of running on Windows 7 was issued June 29, 2011.

A document aimed at developers continues to state that, "When it's released, Internet Explorer 10 will be available for Windows 7, Windows 8, Windows Server 2008 R2, and Windows Server 2012."

A Microsoft spokeswoman today confirmed that the company is committed to producing a Windows 7 edition of IE10. But users want to know more, including when.

"I do have the latest Windows 8 Release Preview but I am wondering what is taking so long for IE10 to be available for testing on Windows 7," asked a user earlier this month on Microsoft's IE10 support forum.

Last November, Microsoft said it would ship beta and RC, or "release candidate," builds of IE10 for the current OS. "We will release an IE10 Beta and Release Candidate on Windows 7 prior to IE10's general availability," said a commenter labeled as "ieblog" - presumably Microsoft itself - in a November 29, 2011, blog post by the team.

But it's not clear whether those plans are still in place: "General availability" of IE10, at least on Windows 8, is likely just four or fewer months away.

Today, Microsoft declined to comment on whether it will, in fact, deliver pre-release builds of IE10 for Windows 7 before it ships the final browser.

Users and web developers chastised the company for not releasing previews of IE10 on Windows 7, arguing that silence hurts the browser's chances of adoption.

"You will not catch some of the bugs in IE10 that happen only on Windows 7 because no one tests it on Windows 7," said someone identified as "KS" last year in a comment on the November 2011 IE blog post. "You have been trying to not repeat your old mistakes. But that doesn't help if you make new mistakes with eyes wide open."

The biggest questions - when does Microsoft plan to ship IE10 for Windows 7 and whether that edition will be identical, or merely similar, to the one for Windows 8's desktop - also remain unanswered.

Some have speculated that IE10 won't appear on Windows 7 until Microsoft ships the second service pack, or SP2, for the operating system. Based on the track record of Windows XP and Vista, Windows 7 SP2 is nearly overdue: Microsoft delivered SP2 for Windows XP just over three years after that edition's launch, and Vista SP2 two years and three months after Vista's debut. Windows 7 launched in October 2009.

Microsoft also declined to comment when asked how IE10 would be issued to Windows 7 customers.

That question is important: Last December, Microsoft announced it would automatically upgrade IE so that users ran the newest version suitable for their copy of Windows. Under the plan, Windows XP users still on IE6 or IE7 would be updated to IE8, while Windows Vista or Windows 7 users running IE7 or IE8 would be pushed to IE9.

Previously, Microsoft had always asked users for their permission before upgrading IE from one version to the next, even if Windows' automatic updates was enabled. If Microsoft applies that new practice to IE10 and Windows 7, it could automatically upgrade IE8 and IE9 on that OS to IE10 without informing users.

When asked whether the "silent upgrade" would apply to IE10 on Windows 7, and if so, whether it would do so at the launch of the new browser or at some later date, the Microsoft spokeswoman used the company's usual "no comment" phrasing of: "We have no information to share."

The absence of IE10 on Windows 7 makes moot analysts' predictions last year that Microsoft was moving toward an annual release cycle for the browser. They came to that conclusion after Microsoft announced IE10 just weeks after the March 2011 release of IE9.

"They don't want to be in the three- or even two-year cycle," Al Hilwa, an analyst with IDC, said at the time, referring to the 29 months between IE7 and IE8, and the 24 months between IE8 and IE9. "They got the memo on that. It doesn't work for browsers, or for any piece of software for that matter."

If Windows 8 ships in October, as most experts expect, the span between IE9 and IE10 would be approximately 19 months.

The desktop edition of IE10 will run only on Windows 7, Windows 8, Server 2008 R2 and Server 2012. Windows Vista, the 2007 operating system that never really caught on with users, cannot run IE10, and instead will be stuck at IE9, just as Windows XP can run no version newer than IE8.

Microsoft was the first browser maker to drop Vista from the support list of a new browser, just as it was the first - and so far, only - vendor to abandon Windows XP.

The company may not care about Vista: The 2007 OS powered just 7% of all Windows PCs that went online last month, according to web metrics company Net Applications.