Microsoft shipped four non-security updates specific to Windows 8 on Tuesday, which doesn't go on sale until Oct. 26. The massive 170MB download for Windows 8 x64 targeted performance, power management, media playback and compatibility issues which company developers uncovered and/or addressed since early August, when Microsoft tagged Windows 8 with the RTM, or "release to manufacturing," label.
In Microsoft's terminology, RTM designates the point at which it considers the code completed, and ready to ship to computer makers for installing on new PCs. Microsoft has never updated a version of Windows between RTM and when the OS hits retail and PCs powered by it reach stores.
Source: PC World