I think you may be mis-remembering something. I am not sure what. QNX was and is very small, but not small enough to run inside a CPU's cache when it was curre

I think you may be mis-remembering something. I am not sure what. QNX was and is very small, but not small enough to run inside a CPU's cache when it was current and in the news, no. Today, yes, but not in 2kB! 2MB, more like. The product I can recall that ran inside a CPU's cache was Symbolics OpenGenera. Genera is an OS written in Lisp for Symbolics Lisp machines. I.e. a CPU that ran a Lisp-like bytecode. https://en.wikipedia.org/wiki/Genera_(operating_system) https://en.wikipedia.org/wiki/Genera_(operating_system) To make OpenGenera, a version for non-Lisp hardware, Symbolics wrote a tiny Lisp interpreter for the DEC Alpha which fit inside the Alpha CPU's cache. It was described in their paper at the time (circa 1994): http://pt.withy.org/publications/VLM.html http://pt.withy.org/publications/VLM.html Later, a version of this was built to run on x86-64 Linux: https://archives.loomcom.com/genera/genera-install.html https://archives.loomcom.com/genera/genera-install.html