O'Brien said a specific time frame is difficult to predict, but he did say that Blackcomb was not expected before the end of 2005 or early 2006.
"Any of the server technologies that we were looking toward delivering in Longhorn will be carried forward in the Blackcomb time frame," O'Brien added. "There are no cuts being made."
O'Brien said the decision to eliminate the Longhorn server release reflected customer feedback that Longhorn would emerge too soon after Windows .net Server 2003, which is due to ship early next year.
"Servers are certainly a bit of an expensive implementation for our customers, and giving them server releases that are too close together makes it difficult for them to deploy them," O'Brien said. "We always have to balance our schedules against what the customers feel is the right schedule for them."
Windows .net Server 2003 - codenamed Whistler - originally was scheduled to ship the same time the Windows XP client hit stores in October 2001. But the server operating system was not ready then, and further delays resulted when Microsoft halted production earlier this year for an intensive security review as part of its Trustworthy Computing initiative.
O'Brien said the server team wanted to make sure the Windows .net Server 2003 release is "rock solid" and that it has no intention of rushing it out the door. Key features in the new server operating system include native support for XML and Web services, real-time communications capabilities and improved performance and reliability, he said.
When asked whether the slipping date for Windows .net Server 2003 affected the Longhorn decision, O'Brien said the server team probably could have driven out a release in the same period as Longhorn if it had to do so.
Windows senior vice-president Brian Valentine said Microsoft's goal is to ship client and server operating systems together because "it's very expensive not to".
O'Brien admitted the Longhorn decision would be costly in some ways. "But if it's the right thing for the customer, that's a cost we need to be willing to bear," he said.
The Longhorn client release will not ship before mid-2004 at the earliest, according to Rogers Weed, a corporate vice-president in Microsoft's Windows product management group.