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Lecture 8 - Objectives Become familiar with the operations...

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6/29/2011 1 CNIT 17600 – IT Architectures System Software 1 Objectives 2 Become familiar with the operations of and functions provided by operating systems Explain how an operating system manages processes and threads Understand the role played by each software component in maintaining the integrity of a computer system and its data 8.1 Introduction 3 The biggest and fastest computer in the world is of no use if it cannot efficiently provide beneficial services to its users Users see the computer through their application programs These programs are ultimately executed by computer hardware System software (OS and middleware) is the glue that holds everything together Most important component of system software Operating Systems 4 Where are we at? Operating Systems 5 OS consists of three layers: Kernel, service layer, and command layer Loosely divided between: Those oriented to hardware resources Those oriented to users and their programs This separation makes the OS more maintainable Functions within one layer can be modified without affecting other layers Management Functions Operating Systems 6 Management Functions
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6/29/2011 2 Operating Systems 7 Layers User’s interface to OS Sometimes called the shell Contains set of functions executed by application programs and the command layer Requested via service call Managed resources and directly interacts with system hardware 8.2 Operating Systems 8 The evolution of operating systems has paralleled the evolution of computer hardware As hardware became more powerful, operating systems allowed people to more easily manage the power of the machine In the days when main memory was measured in kilobytes, and tape drives were the only form of magnetic storage, operating systems were simple resident monitor programs The resident monitor could only load, execute, and terminate programs 8.2 Operating Systems 9 In the 1960s, hardware has become powerful enough to accommodate multiprogramming , the concurrent execution of more than one task Multiprogramming is achieved by allocating each process a given portion of CPU time (a timeslice ) Interactive multiprogramming systems were called timesharing systems When a process is taken from the CPU and replaced by another, we say that a context switch has occurred 8.2 Operating Systems 10 Today, multiprocessor systems have become commonplace They present an array of challenges to the operating system designer, including the manner in which the processors will be synchronized, and how to keep their activities from interfering with each other Tightly coupled multiprocessor systems share a common memory and the same set of I/O devices Symmetric multiprocessor systems are tightly coupled and load balanced 8.2 Operating Systems 11 Loosely coupled multiprocessor systems have physically separate memory These are often called distributed systems Real time operating systems control computers that
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