Distributed environment situation even more complex

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! Distributed environment situation even more complex. " Several copies of a datum can exist. " Various solutions covered in Chapter 17.
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Introduction to OS 33 65 I/O Subsystem ! The purpose of I/O subsystem of the operating system is to hide peculiarities of hardware devices from the user. ! I/O subsystem responsible for " Memory management of I/O including buffering, caching, spooling. " General device-driver interface . " Drivers for specific hardware devices. ! Covered in Chapter 13. 66 Protection and Security ! A multi-user computer system allows the concurrent execution of multiple processes. " Computation resources must be operated in a proper and authorized manner. # For example, a process can execute only within its own address space. ! Protection – any mechanism for controlling access of processes or users to resources defined by the operating system. ! A system can have adequate protection but still be prone to failure and allow inappropriate access. " A user s authentication information is stolen. ! Security – defense of the system against internal and external attacks. " Huge range, including denial-of-service, viruses,
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Introduction to OS 34 67 Protection and Security (cont’d) ! Protection and security require the operating system to be able to distinguish among all its users. ! Most systems maintain a list of user names and associated user identifiers (user IDs, security IDs) . " User ID is then associated with all files, processes of that user to determine access control. ! Group identifier (group ID) allows set of users to be defined and managed, then also associated with each process, file. ! Privilege escalation allows user to change to effective ID with more rights for an activity. " For example, on UNIX, the setuid attribute on a program causes that program to run with the user ID of the owner of the file, rather than the current user’s ID. 68 Distributed Systems ! Is a collection of computer systems that are networked to provide the users with access to various resources. " Access to a shared resource increases computation speed, data availability, … " For example, NFS (network file system) generalize network access as a form of file access. ! Network: " Protocols: TCP/IP, ATM … " Distances: LAN (local area network), WAN (wide-area network) … " Transmission media: copper wires, fiber, wireless …
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Introduction to OS 35 69 Special-Purpose Systems ! Embedded Systems: " A special-purpose computer system designed to perform one or a few dedicated functions. # E.g., robotic arms. " Usually have little or no user interface. " Almost run real-time operating systems . # Rigid time requirements have been placed on the operation of a processor or the flow of data. ! Multimedia Systems: " A recent trend in technology is the incorporation of multimedia data into computer system. " Different from convention data, multimedia data must be delivered according to a certain time restrictions. " Chapter 20 explores the nature of multimedia data and the design of operating systems that support the multimedia. 70 Special-Purpose Systems (cont’d) ! Handheld Systems: " Such as PDAs, usually have a small amount of memory, slow processors, and small display screens because of their size.
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  • Spring '12
  • GwangS.Jung
  • OS, main memory

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