SIW - System Information for Windows
"Everything you want to know about your computer"
For example, you can start advanced tools such as Regedit to load registry hives and modify service status. By default, the registry editor loads the Windows RE environment's registry hive; you need to load the hives from the \%systemroot%\system32\config folder to make changes to the OS environment.
You usually access Windows RE from the Windows 7 (or Vista) installation media. After selecting your preferred language, click Next, then click "Repair your computer." A list of Windows 7 (or Vista) installations appears. You can add additional drivers to see other installations that are using non- bundled drivers. After selecting an OS, click Next.
The full list of options appears, including the ability to automatically repair an environment, revert to a previous system restore point, restore the computer from a backup, run the memory diagnostic tools, or open a command prompt for advanced system-recovery options.More about WinRE here.