The world's largest software maker postponed the consumer version of Vista until next January from the second half of this year But it said that it would ship the next version of its operating system to business customers in November.
Vista is the first big overhaul of Windows since Microsoft released Windows XP nearly five years ago.
Microsoft had been expected to release Windows Longhorn, now Vista, last year. The company cut back its features and pushed it out to 2006 before this latest delay.
The eight- to 10-week delay, according to estimates by research firm Gartner, may reverberate throughout the industry from PC manufacturers to chip-makers and down the supply chain.
David Smith, an analyst at Gartner, said: "It is a critical eight to 10 weeks for retailing and for the producers. The retailers and PC hardware manufacturers work on razor-thin margins, so the impact there could be pretty severe."
Investors, concerned about the impact on PC sales, pushed down shares of chip-maker Intel Corp and large PC manufacturers Hewlett-Packard and Dell in after-hours trade.
Windows, which is found in about 90% of all computer desktops, is Microsoft's biggest earner.
Jim Allchin, co-president of the company's platforms and services division, said: "We could have just gone ahead, but I didn't think it was the right thing to do."
Microsoft says it is still working
on improving overall quality
Microsoft said the delay was to improve overall quality, particularly in security, and that PC makers did not want the operating system introduced in the middle of holiday sales, because a new version would create instability in the market.
The delay also pertains to Vista loaded on new PCs.
Microsoft plans to conduct a consumer beta, or test, of Windows Vista for two million users in the coming quarter.