mod06 - CS 230 Introduction to Computers and Computer...

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CS 230 - Winter 2011 6-1 CS 230 – Introduction to Computers and Computer Systems Module 6 – Operating Systems Martin Karsten [email protected]
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CS 230 - Winter 2011 6-2 Overview basic mechanisms virtual memory disks and file systems inter-process communication
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CS 230 - Winter 2011 6-3 What is an Operating System? OS provides execution environment for running programs programming and service interfaces resource management isolation and protection mediation between program(s) and resources: CPU memory I/O devices
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CS 230 - Winter 2011 6-4 Interfaces and Abstractions low-level interfaces are tedious/cumbersome direct access to hardware OS provides high-level abstractions files and file systems stream abstraction for other devices local and remote communication memory allocation
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CS 230 - Winter 2011 6-5 Multiprogramming process: program in execution address space – private region of memory thread(s) other associated resources, e.g., file handle multiprogramming: multiple processes at the same time all processes share available hardware OS ensures that processes are isolated
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CS 230 - Winter 2011 6-6 Protection / Isolation isolation between multiple programs protection from undesirable interactions ...intended or unintended for functional and security considerations CPU hogging – denial of service memory, e.g. stack, compromised – crash device access – read password write access – fabrication etc. – many possible problems and threats!
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CS 230 - Winter 2011 6-7 Privilege Levels CPU can be in one of several “privilege levels” at least two, possibly more level described by (parts of) a CPU status register some operations only possible at “high” level “high” often means numerically lower special instructions read and/or write certain registers access to certain memory regions
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CS 230 - Winter 2011 6-8 Privilege Levels usually form hierarchy, “protection rings” everything allowed in level x is also allowed in x-1 privileges are checked at each instruction in hardware well-defined narrow interface to change level with well-defined side effects (cf. system calls later)
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CS 230 - Winter 2011 6-9 Operating System Components kernel special “process” managing the system mediates between applications and hardware operating system kernel utility programs command shells programming libraries etc.
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CS 230 - Winter 2011 6-10 Asynchronous Communication process –> kernel: system calls special routine calls that invoke the kernel process <–> process via OS kernel through system calls or shared memory – uncontrolled device –> kernel: interrupts asynchronous hardware notifications
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CS 230 - Winter 2011 6-11 Schematic View Kernel process process process system calls process resume device device device device interrupts user space kernel space trap
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This note was uploaded on 09/28/2011 for the course CS 230 taught by Professor Bb during the Spring '11 term at Waterloo.

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mod06 - CS 230 Introduction to Computers and Computer...

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