L2-Structure.pdf - Lecture 2 OS Structure II microkernels...

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University of Toronto, Department of Computer Science Lecture 2: OS Structure II microkernels, exokernels, virtual machines & modules CSC 469 / CSC 2208 Fall 2017 Bogdan Simion
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University of Toronto, Department of Computer Science Overview Kernel structures Layered systems Open systems Monolithic kernels • Microkernels Kernel Extensions Virtual Machines
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University of Toronto, Department of Computer Science Early Layered System: THE Djikstra, 1 st SOSP, 1967 Disk CPU Keyboard Memory Processor   Allocation   and   Timer   Interrupt   Handling Segment   Controller   (Memory   Management) Message   Interpreter   (console   handler) Buffering   of   input   &   output   data   streams User   programs Operator TTY   out Peripherals
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University of Toronto, Department of Computer Science Properties of Layered Systems Each layer has well-defined function and interface to layer above/below Provides easier-to-use abstraction for higher layers Other examples: MULTICS (rings) Advantages? Each layer can be designed, implemented and tested independently Processes at any level can only invoke services of level below no circular wait no deadlock Disadvantages? Hard to partition functions into this strict hierarchy (why is console below other peripherals?)
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University of Toronto, Department of Computer Science Open Systems Kernel   and   Applications Disk CPU Network Memory Interprocess   Communication File   System Virtual   Memory Networking Apache Mozilla Emacs libpthread libc
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University of Toronto, Department of Computer Science Properties of Open Systems Applications, libraries, kernel all in the same address space Crazy? Idea first described by Lampson & Sproull, 7 th SOSP, 1979 “An open operating system for a single-user machine” MS-DOS; Mac OS 9 and earlier; Windows ME, 98, 95, 3.1 Palm OS and some embedded systems Used to be very common Advantages? Very good performance, very extensible, works well for single-user Disadvantages? No protection between kernel and/or apps, not very stable, composing extensions can lead to unpredictable behavior
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University of Toronto, Department of Computer Science Properties of Open Systems Why is Windows 95/98/ME classified as “open”? 32-bit applications have own address space BUT 16-bit Win, DOS apps, and dll’s share 1GB space Including key system dll’s (kernel32.dll) Next up: monolithic OSs and microkernels…
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University of Toronto, Department of Computer Science Monolithic OS Disk CPU Network Memory Kernel Apache libc libpthread Mozilla libc libpthread Emacs libc CPU   Scheduling Interprocess   Communication Networking Security Virtual   Memory File   System
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University of Toronto, Department of Computer Science 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
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