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Microsoft last night released Internet Explorer 9, the latest version of its widely used web browser. Download it here, but keep in mind that it only works with Windows Vista or Windows 7. The browser isn’t compatible with Windows XP, and Microsoft doesn’t make IE for Mac (or Linux).

[Follow-up: IE9 hits 2.3M: Firefox 4 set for March 22]

Given the large market share still enjoyed by Windows XP — more than 44 percent, by one measure — Microsoft is taking a gamble by not making a version of IE9 for the older operating system. But keep in mind that when we say “older” in this context, we really mean it. Windows XP was released nearly a decade ago, and the only reason it still has such a grip on our lives is that Windows Vista was delayed for so long, and received so poorly.

Tony Bradley of PCWorld defends Microsoft’s decision in this post today

“Microsoft could have developed a browser that was an incremental improvement over Internet Explorer 8 just for the sake of developing a new browser, and it could have maintained backward compatibility with Windows XP. However, doing so would greatly restrict what Microsoft is able to accomplish with that browser. At some point you have to cut the cord and move on to embrace the future rather than continuously coddling the past.”

[Previously: Inside IE9: How Microsoft rewrote its browser from scratch]

Ars Technica’s Peter Bright agrees in his review of IE9 (which deserves to be read in full).

“The performance improvements made by the use of DirectWrite and Direct2D allow a new class of Web application to be developed. They greatly extend the range of what is possible and practical to do on a website. Platform security features that Internet Explorer 9 leverages also make the switch to more modern operating systems desirable. Some of the things that make IE9 a better browser are things that simply do not exist on Windows XP.”

Also check out the performance benchmarks run by Adrian Kingsley-Hughes of, comparing IE9 to Chrome, Firefox and Opera — and showing just how competitive the browser market remains.

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