To study how chips really work, MIT researchers built their own operating system

A fascinating novel approach by researchers at MIT, called Fractal, to study in-depth how processors actually work.

A team at MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) decided to build something different. Fractal, an operating system kernel written from the ground up, treats the hardware itself as the object of study. Its first major use, a deep look at branch predictors - a CPU's way of guessing what code to run next, before it knows for certain, so it doesn't have to waste time waiting to find out - inside Apple's M1 processor, has already turned up findings that prior work missed, including the first evidence that a class of speculative attack known as Phantom" affects Apple Silicon.

We're using hardware in ways it wasn't designed for," says Joseph Ravichandran, the MIT PhD student in electrical engineering and computer science (EECS) who led the project. It's not even obvious that this is a possible thing you could do with the hardware. But we found a way to pull all these different primitives off. It's like a microscope. If you've got a hand magnifying glass, you can see a little bit. But if you had an electron microscope, now we're really talking. That's what Fractal is. The electron microscope of operating systems."

Rachel Gordon at MIT News

While Fractal is small, its creators also added POSIX system calls, a C library, vim, GCC, a shell, and more. This way, it feels more familiar, and makes it easier for researchers to get started with the tool. Fractal is open source and hosted on GitHub, it has its own website, and there's a detailed research paper with more in-depth information.