Protection System Protection refers to a mechanism for controlling access by

Protection system protection refers to a mechanism

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Protection System Protection refers to a mechanism for controlling access by programs, processes, or users to both system and user resources. The protection mechanism must: distinguish between authorized and unauthorized usage. specify the controls to be imposed. // 定義法律 provide a means of enforcement. // 執行法律 Networking (Distributed Systems) A distributed system is a collection processors that do not share memory or a clock. Each processor has its own local memory. The processors in the system are connected through a communication network. A distributed system provides user access to various system resources. Access to a shared resource allows:
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3 Computation speed-up Increased data availability Enhanced reliability Command-Interpreter System Many commands are given to the operating system by control statements which deal with: process creation and management I/O handling secondary-storage management main-memory management file-system access protection networking Command-Interpreter System (Cont.) The program that reads and interprets control statements is called variously: control-card interpreter command-line interpreter shell (in UNIX) Its function is to get and execute the next command statement. Operating System Services Program execution – system capability to load a program into memory and to run it. I/O operations – since user programs cannot execute I/O operations directly, the operating system must provide some means to perform I/O. File-system manipulation – program capability to read, write, create, and delete files. Communications – exchange of information between processes executing either on the same computer or on different systems tied together by a network. Implemented via shared memory or message passing . Error detection – ensure correct computing by detecting errors in the CPU and memory hardware, in I/O devices, or in user programs. Additional Operating System Functions Additional functions exist not for helping the user, but rather for ensuring efficient system operations. Resource allocation – allocating resources to multiple users or multiple jobs running at the same time. Accounting – keep track of and record which users use how much and what kinds of computer resources for account billing or for accumulating usage statistics. Protection – ensuring that all access to system resources is controlled. System Calls
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4 System calls provide the interface between a running program and the operating system. Generally available as assembly-language instructions. Languages defined to replace assembly language for systems programming allow system calls to be made directly (e.g., C. Bliss, PL/360) Three general methods are used to pass parameters between a running program and the operating system.
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