Today marks an important milestone for Windows 7: the arrival of its first service pack since the operating system's release in late 2009.

Service Pack 1 was released to manufacturers earlier this month, with the announcement that it would arrive in consumers' hands this week. The software is set to hit Windows Update later today, with it already being posted as a 1.95GB download bundle for all versions on Microsoft's Download Center. TechNet subscribers and Microsoft volume license customers got access to the update last week.

Microsoft says the standalone update package should weigh in at 527MB for x86 users, about 903MB for x64 users, and 511MB for users on Itanium chips. In Windows Update, the download sizes are much smaller:

Windows 7 SP1 download sizes (by delivery method)

The service pack doesn't bring any new whiz-bang features for consumers, but it includes two important back end additions that promise to improve performance in Windows 7's server counterpart, Windows Server 2008 R2. The update adds Dynamic Memory and RemoteFX, technologies that increase, respectively, the density of virtual machines and the graphical prowess of thin-client hardware (more on those here). The RemoteFX feature is also coming to the consumer version of Windows 7 in the form of client-side support.

Also included in SP1 are a number of fixes for bugs and security holes, which may be useful for those who don't use the auto-update feature or are applying the update to machines that don't have an active Internet connection. Other small changes include improved HDMI audio-device performance, a fix for printing mixed-orientation XPS documents, and "improved support" for Advanced Format storage devices.

SP1 first appeared in beta form in July of last year, with its first release candidate hitting the company's testing channels in October. Leaks of the release for the manufacturers' version of the software appeared on file-sharing networks last month.