Longhorn, the next version of Microsoft Corp.'s Windows desktop operating system, will be so different from its predecessors that users may not like it right away, said Microsoft chairman Bill Gates.

"Longhorn is a bit scary. ... We have been willing to change things," Gates said at Microsoft's annual financial analyst meeting at the company's Redmond, Washington, headquarters.

"It (Longhorn) should drive a whole range of upgrades, but that could be sort of delayed," Gates said. Because of differences with the previous versions of Windows, it could be a year or two after its release before computer users really pick up Longhorn, he said.

Gates appeared to distance himself from a commitment the company made at its Windows Engineering Hardware Conference (WinHEC) in May to deliver Longhorn in 2005. This time, he would not comment on the release date.

"Longhorn is innovative ... there is a lot of work to be done in terms of what has to go in and what has not," Gates said. Asked if Microsoft would consider dropping some of the innovations it has planned so the product can come out sooner, Gates said no: "If you split it up, then you delay one of the really great pieces," he said.

"We need a big bang release to drive excitement," Gates said.

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Microsoft has been tightlipped about specific features in Longhorn, but early versions of the product have leaked to the Internet. Major changes in Longhorn are expected to include the graphical user interface and either a new file system or a technology update to the existing file system.

Gates said that Longhorn will have a new file system, but Microsoft officials at WinHEC said the operating system will have a new storage system that will be based on the existing NTFS.

Microsoft promises more details about the operating system release, which analysts have said will be one of the most important Windows launches for Microsoft, in October at the Microsoft Professional Developers Conference to be held in Los Angeles. A beta of Longhorn is planned for next year.