What ever happened to Tandem and NonStop OS 2020

This is where Linus had some run-ins with this group a few years ago. It had to do with a posting I made to a "what do we still miss from systems of old".

The last bit of "ancient stuff" I still miss sorely is the ring systems from Multics and it's renegade son Primos. A simplar simpler, but still effective isolation system is present in QNX and Mach.

It involves nuking the "userspace-kernelspace" dictonomy, and make "ring x space" instead.

In modern OS'es an extremely low percentage of code actually need kernel priviliges. Most of this code is already in drivers and their interface code.

All the rest of stuff belongs outside the core "ring 0" space. So far, the "kernel-user" system hasn't had anywhere else to put it, because it DOES need higher priviliges than the users.

Isolate it. Put proper interfaces around it, and let it run in ring 1. There is an added advantage in that ring1 stuff can enjoy a lot of the things that make user space easier to program in. It can run in proper virtual memory, can access process and other services from the kernel etc.

When you build and debug it you can even run it in normal (ring3) user space. You just need to demote a set of programs to ring4, e.g. a shell, and let the ring3 process service it.

File systems scream for such implementations.

It also makes good "program jails" for server processes you want encapsulated. Demote them to ring 7 and give them service (and security!) processes in higher rings.

-- mrr