Advanced Operating Systems   COMP9242 2002/S2

UNSW

Printer-Friendly Version Administration                - Notices - Course Intro - Consultations # On-line Survey (closed) - Survey Results   Work - Lectures - Milestone 0 - Project Admin - Project Spec - Project FAQ - Exam   Documentation - ASysT Lab - L4 source browser - Sulima ISA Simulator - R4x00 ISA Summary  - MIPS R4700 Reference - MIPS R4000 User Manual  - Network Driver - GT64111   Related Info - Aurema OS Prize - OS Hall of Fame   History - 2000 - 1999 - 1998   Staff - Gernot Heiser (LiC)

Motivation Early operating systems had very little structure. A strictly layered approach was promoted by [Dijkstra 1968]. Later OS (more or less) followed that approach (e.g., Unix). Problems with layered approach Widening range of services and applications ==> OS bigger, more complex, slower, more error prone. Need to support same OS on different hardware. Like to support various OS environments. Distribution ==> impossible to provide all services from same (local) kernel. Idea: break up the OS Monolithic vs. client-server OS structure Kernel:  $.$ Contains code which must run in supervisor mode;  $.$ Isolates hardware dependence from higher levels;  $.$ Is small and fast ==> extensible system;  $.$ Kernel provides mechanisms. User-level servers: Are hardware independent/portable, Provide ``OS environment''/''OS personality'' (maybe several), May be invoked: from application (via message-passing IPC) from kernel (upcalls); Servers implement policies[BH70].