Microsoft this week quietly delivered a public Release Candidate 1 (RC1) version of Service Pack 1 (SP1) for Windows 7 and Windows Server 2008 R2. The company also confirmed a report that first appeared in WinInfo back in June: The final version of SP1 won't ship until the first quarter of 2011.

"This release candidate signals the last public beta build to be released prior to the Release to Manufacturing (RTM) final release," a curiously awkward Microsoft statement reads.

Because Windows 7 and Server 2008 R2 were co-developed, SP1 services both releases. However, it has sharply different effects on the two OSs. With Windows 7, users will simply get a traditional service pack, offering a rollup of previously delivered security updates and other hot-fixes. (SP1 does include a minor update to the remote desktop client in Windows 7, as well.) With Server 2008 R2, however, SP1 offers some major functional enhancements.

These include two virtualization-related features that bolster Server 2008 R2's Hyper-V functionality, Dynamic Memory and RemoteFX. Dynamic Memory provides Hyper-V with the ability to change the RAM allocated to virtual machines (VMs) on the fly. RemoteFX enables the delivery of graphics-rich environments to thin clients (or PCs).

SP1 RC1 is available in separate 32-bit and 64-bit installers. You can download the RC1 version of SP1 for Windows 7 and Server 2008 R2 from the Microsoft website.