I believe Singularity enforces application security by validating the safety of the application code. This is completely different from the security mechanisms

I believe Singularity enforces application security by validating the safety of the application code. This is completely different from the security mechanisms of Windows and Unix, which are based on protecting memory and separating the kernel and applications with a carefully checked interface. I doubt that much existing OS code would be useful for the new OS. Singularity is really exciting. There are some big potential efficiency gains with this kind of OS. The biggest one is in reducing the number of context switches performed by the computer. A context switch is when the OS replaces the CPU's registers, saving the current values and reading in new ones. This takes time and can push application data out of the cache. With current OS's, every kernel call results in two expensive context switches. One to enter kernel mode and another to return to the application. In Singularity, an application's call into the OS shouldn't require a context switch.