Jean-Pierre Paradis's Blog: What's the new /NoExecute switch that's added to the boot.ini file after you update a machine to Windows Server 2003 Service Pack 1 (SP1) or Windows X

John Savill wrote at WindowsITPro :

The /NoExecute switch relates to the new data execution prevention (DEP) technologies that Microsoft introduced in Windows 2003 SP1 and Windows XP SP2. DEP technologies help stop malicious code from accessing data pages. Two types of DEP technologies exist: software-enforced and hardware-enforced. The table shows the four parameters you can use with the /NoExecute switch.

The following sample boot.ini file includes the /NoExecute switch: multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional" /fastdetect /NoExecute=OptIn