They were trying to build the entire OS using a 100% memory-safe language. At one point they could elide process boundaries and protected memory (and the associ

They were trying to build the entire OS using a 100% memory-safe language. At one point they could elide process boundaries and protected memory (and the associated context switch overhead) because the loader could statically verify your program didn't do anything unsafe. The ultimate answer to Singularity/Midori/etc is yes, you can have an OS (including drivers and interrupt handlers) that is 100% provably memory safe and thread safe and is performance-competitive with existing systems. Unfortunately Microsoft basically sheleved most of the work and it doesn't look like anyone else is going to pick up the slack. I predict more heartbleeds and zero-day RCEs in our future. At least we'll all get 0wned with fast C code.