Protection mechanisms must Distinguish between authorized and unauthorized use

Protection mechanisms must distinguish between

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° Protection mechanisms must: ± Distinguish between authorized and unauthorized use. ± Specify access controls to be imposed on use. ± Provide mechanisms for enforcement of access control. ± Security mechanisms provide trust in system and privacy ° authentication, certification, encryption etc.
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Networking (Distributed Systems) ° Distributed System is a collection of processors that do not share memory or a clock. ° Processors are connected via a communication network. Advantages: ° ± Allows users and system to exchange information ± provide computational speedup ± increased reliability and availability of information
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System Design and Implementation ° Establish design goals ± User Goals ± System Goals ° Software Engineering - ± Separate mechanism from policy. Policies determine what needs to be done, mechanisms determine how they are done. ° Choose a high-level implementation language ± faster implementation, more compact, easier to debug
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System Generation ° OS written for a class of machines, must be configured for each specific site. ± SYSGEN program obtains info about specific hardware configuration and creates version of OS for hardware ° Booting ° Bootstrap program - loader program loads kernel, kernel loads rest of OS. ± Bootstrap program stored in ROM
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OS Structure - Simple Approach ° MS-DOS - provides a lot of functionality in little space. ± Not divided into modules, Interfaces and levels of functionality are not well separated ° UNIX - limited structuring, has 2 separable parts ± Systems programs ± Kernel ° everything below system call interface and above physical hardware. ° Filesystem, CPU scheduling, memory management
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UNIX System Structure
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Layered OS Structure ° OS divided into number of layers - bottom layer is hardware, highest layer is the user interface. ° Each layer uses functions and services of only lower- level layers. ° THE Operating System Kernel has successive layers of abstraction.
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Virtual Machines ° Logically treats hardware and OS kernel as hardware ° Provides interface identical to underlying processes processes bare hardware. ° Creates illusion of multiple processes - each with its own processor and virtual memory hardware Virtual machine kernel kernel kernel processes
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Summary of OS Structures ° Operating System Concepts ° Operating System Services, System Programs and System calls ° Operating System Design and Implementation ° Structuring Operating Systems
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