MicrokernelsCS-502 (EMC) Fall Microkernels CS-502, Operating Systems Fall 2009 (EMC) (Slides include materials from Modern Operating Systems, 3 rd ed., by Andrew Tanenbaum and from Operating System Concepts, 7 th ed., by Silbershatz, Galvin, & Gagne)

MicrokernelsCS-502 (EMC) Fall Problem Operating systems are large They continue to evolve and grow … and are worked on by many people (Like all other programs) they contain bugs How to organize them so that bugs do not … bring down systems … impede normal operation … etc.

MicrokernelsCS-502 (EMC) Fall Operating System Structures Monolithic systems Formerly called “the big mess” Layered systems Microkernel based systems Client-server model Virtual Machines Exokernels Tanenbaum, §1.7 An epithet leveled at any big system by a speaker who does not understand & and made by someone s/he does not trust!

MicrokernelsCS-502 (EMC) Fall Operating System Structures Monolithic systems Formerly called “the big mess” Layered systems Microkernel based systems Client-server model Virtual Machines Exokernels A faulty driver or component can corrupt any data in kernel Arbitrary damage Stop system anywhere … etc.

MicrokernelsCS-502 (EMC) Fall Layered Systems Figure Structure of the THE operating system. Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved

MicrokernelsCS-502 (EMC) Fall Layered Systems Figure Structure of the THE operating system. Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved Simple Elegant Incredibly naïve

MicrokernelsCS-502 (EMC) Fall Microkernel — An Organizing Principle Partition OS kernel into lots of small, independent pieces Put pieces in separate “processes” Isolated from each other except for message passing Keep kernel mode code to a minimum Concept emerged in 1970s MACH at CMU (Rick Rashid) NEXT computer Apple Mac-OS

MicrokernelsCS-502 (EMC) Fall Microkernel Example Figure Structure of the MINIX 3 system. Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved

MicrokernelsCS-502 (EMC) Fall Microkernel Example Figure Structure of the MINIX 3 system. Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved Works great on a PDP-11 Memory addressable device registers Minimal interrupt handling, scheduling, IPC, etc No virtual memory management

MicrokernelsCS-502 (EMC) Fall Microkernel Issues Virtual memory management Needs to interact directly with scheduler Page faults, etc. Kernel support for user-space threads Fast I/O devices Quick, responsive interrupts Top- and bottom-halves for interrupt handlers Interprocess communication … On every context switch! Cannot afford context switches Remember Project #4

MicrokernelsCS-502 (EMC) Fall Microkernel Meets the Real World Windows NT Started life as a microkernel No longer “micro” No longer a kernel!

MicrokernelsCS-502 (EMC) Fall Figure The programming layers in Windows. Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved One View of Windows Vista

MicrokernelsCS-502 (EMC) Fall Figure The components used to build NT subsystems. Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved Another View of Windows Vista

MicrokernelsCS-502 (EMC) Fall Figure Windows kernel-mode organization. Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved A Third View of Windows Vista

MicrokernelsCS-502 (EMC) Fall Lesson — Windows Vista There are a lot of layers of abstraction Many of the pieces are operate in separate address spaces An other isolation Most of Vista operates outside kernel mode

MicrokernelsCS-502 (EMC) Fall Microkernels A good idea in the 1970s and 80s Not up to demands of modern processors Virtual memory Heavy caching Not up to demand of modern operating systems

MicrokernelsCS-502 (EMC) Fall Microkernel Resurrection Mobile phones, PDAs, handheld devices Fixed or limited functionality No general purpose files No dynamic virtual memory  Simple context switches All code already in memory Easy IPC

MicrokernelsCS-502 (EMC) Fall Questions or Discussion?