Kris Ambrose 2003 1

Mach Kernel

Kris Ambrose

Kris Ambrose 2003 2

Overview

• A research project at Carnegie Mellon University (CMU) from 1985 to 1994.

• Considered to be the next great operating system

• Designed to incorporate many new OS technologies– Microkernel

– Multiprocessing

– Interprocess Communication (IPC)

– Distributed Operation

– Portable across heterogeneous hardware

• And still maintain BSD Unix compatible

Kris Ambrose 2003 3

Mach Kernel Abstractions• Task – a basic unit of resource allocation that must contain an address

space and may contain port rights and threads.

• Thread – a basic unit of CPU utilization that belongs to a task and uses the task’s resource allocation.

• Port – a communication channel that the kernel protects, allows for all parts of the kernel and tasks to pass messages back and forth.

• Message – a typed collection of data objects that may be actual data, port rights, or a pointer out-of-line-data.

• Memory Object – a basic unit of memory used within the kernel and the a task may access it by mapping parts or all of it into its address space.

Kris Ambrose 2003 4

Mach’s Abstractions

Silberschatz, Galvin, Gagne(2003) Appendix B: Mach

Kris Ambrose 2003 5

Mach as a Microkernel

• Minimizes Kernel Operations– Task and Thread Management– IPC– Virtual Memory

• Acts as a Virtual Machine

• Parts are Modular

Kris Ambrose 2003 6

Structure of Mach

Billard (2001): Mach Design

Kris Ambrose 2003 7

Multiprocessing in Mach

• Threads are scheduled not tasks• Threads are CPU independent• Preemptive Scheduling done with a Priority

Queue• Quantum is based on Number of CPUs and

Threads• Threads to run across many processors• Global and Local Run Queues

Kris Ambrose 2003 8

Interprocess Communication

• Tasks and Threads pass messages

• Ports accept messages

• Port rights are assigned for protection

• Tasks may create Port Sets

• Large Messages use Copy-On-Write

Kris Ambrose 2003 9

Distributed Operation and Portability

• Each Server Contains a different Module

• Fast and Secure reload

• Multiple CPUs may be used for different Modules

• Runs across different Architectures

Kris Ambrose 2003 10

Unix Compatibility

• Allows for Unix System calls

• Mach needs Unix

• Acts as a Virtual Machine

Kris Ambrose 2003 11

Today and Beyond• Many of the Operating Systems today use the

ideas of Mach– QNX– Hurd– Mach 4– Real-Time Mach

• Some Actually Use the Mach/FreeBSD– NeXT– Mac OS X (based on NeXT)– IBM OS/2 for the RS6000 based machines

• The Open Software Foundation (OSF) is still doing further research and development

Kris Ambrose 2003 12

Summary

• Originally CMU and OSF Research Project• Major Accomplishments

– Microkernel– Multiprocessing– Interprocess Communication– Distributed Operations– Portable– BSD Unix Compatible

• Concepts still used

Kris Ambrose 2003 13

The End