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1.1 The Role of Operating Systems - Bridge the
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1. Presentation 1.1 The Role of Operating Systems - Bridge the "Semantic Gap" amongst Hardware and Application - Three Views of Operating Systems 1.2 Organization of Operating Systems - Structural Organization - The Hardware Interface - The Programming Interface - The User Interface - Runtime Organization 1.3 Operating System Evolution & Concepts

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Single CPU System Figure 1-1

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Bridging the Semantic Gap Hardware abilities are low level Arithmetic and intelligent administrators Comparison of no good strings Branching, perusing, and composing bytes User needs to think as far as issue to be explained High-level information structures and relating operations Simple, uniform interfaces to subsystems, Treat projects and information documents as single elements Use programming to extension this hole Language processors (e.g., constructing agents, compilers, mediators). Editors and content processors, linkers and loaders. Application projects, utility and administration programs. Working Systems

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The part of OSs Bridge Hardware/Application Gap Machine guideline versus abnormal state operation compiler spans crevice Linear memory versus information structures compiler spans hole Limited CPU & memory versus more required OS spans hole Secondary memory gadgets versus records OS spans hole I/O gadgets versus abnormal state I/O summons OS spans hole

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Multiprocessor Systems Figure 1-2a Figure 1-2b

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Multicomputer System Figure 1-2c

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PC Hardware Organization Figure 1-7

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Three perspectives of OSs OS is an augmented machine Principle of reflection conceals intricacy OS gives abnormal state operations utilizing lower level operations OS is a virtual machine Principle of virtualization backings sharing OS gives virtual CPU, memory, gadgets OS is an asset chief Balance general execution with individual needs (reaction time, due dates)

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Structural Organization of OSs Monolithic versus Layered Figure 1-8

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Organization of OSs Hardware Interface Applications and OS incorporated into machine directions Interrupts and Traps permit OS to seize control process administration (time-sharing) gadget administration (I/O finish)

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Principles of Interupts and Traps Figure 1-9

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Organization of OSs Hardware interface (proceeded with) Modes of CPU execution Privileged/Nonprivileged SVC (administrator call) causes trap Control moved to OS in advantaged mode OS exits favored mode when coming back to client

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Organization of OSs Programming Interface Invoking framework administrations Library call (nonprivileged) Kernel call (special) Figure 1-8

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Invoking System Services Figure 1-10

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Organization of OSs User interface (cf. Fig. 1-8) Text-based shell (e.g. Unix) charge mediator shell scripts Graphics-based GUI (e.g. Macintosh, MS Windows) W indows I cons M enus P ointer

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Organization of OSs Runtime association Service is a Subroutine Service is an Autonomous Process ("customer server") Figure 1-12

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OS Evolution and Concepts Early frameworks Bootstrapping Batch OSs I/O processors Interrupts Relocatable code Multiprogramming

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Multiprogramming Basic issue: Some projects are register bound, some I/O-bound Even "adjusted" projects are adjust just after some time No one system can make full utilization of the framework Solution: Multiprogramming Have more than one dynamic (running) program in memory at any one time Multiprogramming requires Bridging the semantic hole Sharing assets among various projects Hiding from every system the truth of this sharing

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OS Evolution and Concepts Multiprogramming Systems Overlap CPU and I/O Protection Synchronization and Communication Dynamic Memory Management (swapping and paging) Interactive OSs Guaranteed reaction Time-sharing (quantum)

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OS Evolution and Concepts PC and workstation OSs GUI Real-time OSs Deadlines (planning) Distributed OSs Loosely coupled/firmly coupled Consistent course of events (coherent tickers, time stamps)

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The Virtues of "virtual" = Being such in force, power, or effect, in spite of the fact that not really or explicitly such Exact picture of a genuine (e.g., "virtual machine") Illusion of a Hypothetical (e.g., "virtual memory") Use "reflection" to make "virtual"

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Abstraction E.W.Dijkstra, "The Humble Programmer" (1972): "The motivation behind deliberation is not to be obscure, but rather to make another semantic level in which one can be completely exact." "reflection" is made by recognizing Essential attributes from Unimportant subtle elements Build levels (layers) of reflections: What is immaterial point of interest at one level is a key trademark at a lower one.

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