Microsoft’s forthcoming Windows 7 operating system was released to manufacturing on Wednesday, a milestone that signals the formal completion of the engineering development phase.

Partners and ISVs can work with the final version, with locked-in code and features, as they build out their own solutions heading toward the general availability launch of the products this fall, according to Microsoft.

“Not only is RTM an important milestone for us – it’s also an important milestone for our partners,” wrote one member of the engineering team on the Windows Blog. “Today’s release is the result of hard work and collaboration with our partners in the industry to make Windows 7 a success. We delivered Windows 7 with a predictable feature set on a predictable timetable that allowed OEMs to focus on value and differentiation for their customers.”

Windows 7 is due out in general release on Oct. 22 and has been so far reviewed favorably by partners, who are smarting from the abject failure of Microsoft’s current client OS, Windows Vista, to take any respectable hold in the marketplace. PC manufacturers and hardware resellers are also placing bets that a Windows 7 uptick will drive new sales of systems.

Microsoft said 16,000 partners, including ISVs and OEMs, have been participating in the Windows 7 Readiness program, already building out solutions. Mike Nash, corporate vice president of Windows Product Management, told Channel Insider that solution providers and VARs will find as much opportunity in Windows 7 as their ISV and OEM counterparts.

“What can VARs do? They can help customers running Windows XP to make the move to Windows 7,” he said. “Even with the great work of XP SP2, the gap between it and Windows 7 is significant for the browser, the core OS and other features we’ve enhanced. That’s an opportunity.”

While partners are optimistic about Windows 7’s potential, many still see their fortunes tied to customers finally getting around to the PC upgrade process.

“Most of our customers don’t ever upgrade to a new OS on its own; they do so when they buy new PCs,” said Brian Jaenisch, Microsoft partner business development manager at Marco, in St. Cloud, Minn. “So today, that amounts to a lot of platform work for us around Windows 7.”

IDC is also predicting that Windows 7 adoption will take place quickly, with 177 million units shipped by the end of next year.