Microsoft cited security and compatibility issues for its decision not to develop the next version of its productivity software to work with PCs running Windows ME (Millennium Edition), Windows NT, Windows 98, Windows 98 SE (Special Edition) and Windows 95.
However, the company could alter its plans if it received overwhelming feedback from customers, a spokeswoman said.
The company disclosed its plans after reports surfaced that operating system support in beta testing would be limited.
BetaNews, a Web site devoted to information about products under development, reported that Microsoft first disclosed its plans in a message board for Office 11 beta testers, citing a posting attributed to a Microsoft developer.
"There were a number of reasons for removing support for Windows 9x. As a number of you have noted, Windows 98 and 98 SE are getting a bit old now. It also relates heavily to the push to improve security in our products. Windows 9x is inherently insecure," the posting read, according to BetaNews.
"We understand that this decision won't be popular among all of our customers, but it allows us to create a better and more stable product," it continued.
With a few thousand beta testers currently using and debugging the early code, Microsoft said it is too early to comment on the exact system requirements for the final product.
Office 11 is expected to undergo a wider beta test in the next few months and be released in its final version in mid-2003 with new features that take advantage of the open standard XML (Extensible Markup Language).
Microsoft has in the past dropped support for earlier versions of its operating system with new software releases. For example, Office XP cannot be installed on PCs running Windows 95, according to Paul DeGroot, an analyst with Directions on Microsoft.
"To some extent, Microsoft may just be being fairly realistic about the market. They've got a product that might not run well on the typical Windows 98 machine," DeGroot said.
He also speculated that Microsoft's decision could be an effort to drive more customers to upgrade to its most recent operating system release, a goal that has led to the company's new licensing model, which requires customers to run current versions of Windows.