Multipop
An OS, by Robin Popplestone, first operational in late 1967, which was based on the concurrently developed implemenation of POP-2; Multipop employed no conventional hardware protection mechanisms: its security was guaranteed by accessing system resources via closures of device access functions, and on built in restrictions on code generation embodied in the compiler (an ancient example of a no-kernel system).This page is linked from: Microkernel Debate