Micro Kernel

Lecture 2: OS Structure
CSC 469H1F Fall 2006 Angela Demke Brown

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Overview
• Motivation: Why talk about structure? • Kernel structures
• • • • • Monolithic kernels Open systems Microkernels Kernel Extensions (Tuesday) Virtual Machines (Tuesday)

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Motivation
• Let’s review what OS provides…
• • • • Abstraction layers Protection boundaries Resource allocators Resource schedulers

• It’s complicated!

• Windows NT ~29 million lines of code (as of 2000)

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Week 1

Monolithic OS
Apache
libc libpthread

Mozilla libc libpthread

Emacs libc CPU Scheduling
Kernel

Interprocess Communication Networking File System Virtual Memory

Security CPU Network Memory Disk

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Properties of Monolithic Kernels
• OS is all in one place, below the “red line” • Applications use a well-defined system call interface to interact with kernel • Examples: Unix, Windows NT/XP, Linux, BSD, OS/161 • Advantages?
• Common in commercial systems
• Good performance, well-understood, easy for kernel developers, high level of protection between applications • No protection between kernel components, not (safely, easily) extensible, overall structure becomes complicated (no clear boundaries between modules)
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• Disadvantages?

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Open Systems
Mozilla
Kernel and Applications

libpthread libc Interprocess Communication File System Virtual Memory

Apache

Emacs Networking

CPU

Network

Memory

Disk

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Properties of Open Systems
• Applications, libraries, kernel all in the same address space • Crazy?
• • • • MS-DOS Mac OS 9 and earlier Windows ME, 98, 95, 3.1, etc. Palm OS and some embedded systems

• Used to be very common • Advantages?
• •
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Very good performance, very extensible, works well for single-user OS No protection btwn kernel and/or apps, not very stable, composing extensions can lead to unpredictable behavior
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