OS design principles

0.OS should be as fast as possible.
1.OS should use the least memory, unless it hurts #0.
2.OS should have the most security, unless it hurts #1,#0.
3.OS should have the most compatibility, unless it hurts #2 , #1,#0.
4.OS should have the most features, unless it hurts #3,#2,#1,#0.

If you're making an embedded system like Rockbox, your rules are the best. If it's connected to the Internet, security is king. If you can get rooted just by connecting to the Internet, it's crap. If it automatically downloads and runs executable code a la ActiveX in IE 4, it's crap. If every program has raw access to every device as an ordinary user, it's crap. If there's no memory protection (per-process address spaces, segments, a VM, or type tags), it's crap.