I’m an HPC guy. The only good OS is one that is not executing any instructions except mine. No daemons, no interrupts, nothing. Load my code, give me all physical memory, give me direct access to the interconnect and then get out of the way. If I want anything, I will let you know, but don’t wait up. When I put on an educator’s hat I still have a soft spot for V6 and V7. Those were my first exposure to Unix and the Unix Way. One could actually learn style by reading code and writing device drivers. These days kernels (Linux at least) are too complicated and too cluttered up with ifdefs to learn much. The real recent innovations like RCU and queuing locks and NUMA affinity are buried pretty deep, and actual reliable file systems like ZFS and BTRFS are just too complicated for mortals. As a user, what I really want are reliability, the commands and utilities, and stable APIs. I don’t like a lot of things about Posix, but it is at least a little stable and a little portable. For myself, I use MacOS and Debian Linux, and open, close, read, write. -Larry