Winpe
WinPe
Windows Preinstallation Environment (Windows PE) is a minimal operating system designed to prepare a computer for Windows installation. It can be used to start a computer with no operating system, to partition and to format hard drives,to prepare a computer for Windows installation, to copy disk images, and to initiate Windows Setup from a network share.
Windows PE is not designed to be the primary operating system on a computer, but is instead used as a standalone preinstallation environment and as an integral component of other Setup and recovery technologies.
For more detail please refer to Windows PE Technical Reference http://technet.microsoft.com/en-us/library/dd744322(WS.10).aspx