"We are going to be as transparent as we can be, but we are not promising a final ship date today," he said.
Microsoft has been persistently vague on when the various server and desktop versions of Longhorn will ship, with the year 2007 the most precise estimate so far. Speaking at the conference earlier this week, Paul Flessner, senior vice president of Microsoft's Server Platform Division, also refused to be drawn on an exact release date.
Ballmer confirmed earlier rumours that the delays to the release of the latest update to Windows XP, Service Pack 2 (SP2), had an impact on the schedule for Longhorn, conceding that, "SP2 didn't help the Longhorn schedule," he said.
SP2 was due to ship this month, but earlier this week Microsoft confirmed that the release to manufacturing date had been pushed back to August. This is the second time that Microsoft has delayed SP2, which was originally expected in June. Earlier this year, Microsoft said that the update would be delayed until this month.
The company gave no reasons for most recent delay. Last month, a number of Windows enthusiast Web sites reported that Microsoft had run into compatibility problems between SP2 and other software.
The Microsoft chief was in as vociferous form as ever at the Microsoft Worldwide Partner conference in Toronto, but held off from the stage-dancing that has characterised some of his previous performances, limiting his movements to an aggressive combination of air-punching and fist-clenching.
Ballmer said Longhorn represents a large "step function" in invention which would be disruptive for companies and partners, but that periods of intense innovation, followed by incremental improvements, were the nature of the software industry.
"The software industry is lumpy," he said. "These kinds of step functions are disruptive but the day we ignore them is the day someone else is going to invest in the step functions."
Ballmer told the audience of partners and independent software developers that the disruption around Longhorn would be worth it as Microsoft is attempting to "enable a new wave of applications" with the release.
"I would encourage you not to miss this wave," he said.
He admitted that the company has work to do when it comes to its product road map. "We are not that good at scheduling. We are not as bad as some but we are not as good as others should be."