operating systems

operating systems - Operating Systems D.Lowther 2001, T....

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© D.Lowther 2001, T. Arbel 2003 Operating Systems
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© D.Lowther 2001, T. Arbel 2003 Operating Systems • Software systems that serve computer users and user programs by providing • controlled access to all available hardware facilities, • software utilities to enhance productivity and ease of use, • user interfaces to ease and control communication. • General principle: • User processes communicate with the operating system, operating system communicates with hardware.
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© D.Lowther 2001, T. Arbel 2003 Hardware obsolescence: – Cost of hardware has decreased 35% annually since 1950, probably will continue. – Maintenance costs 10% of purchase price and does not decrease during life of machine. – It may actually increase as equipment grows older and less reliable. – Result: by the 5th year, maintenance of an old machine is costlier than an equivalent new one.
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© D.Lowther 2001, T. Arbel 2003 Software durability: • Substantial software takes a long time to build: • word processor 10 4 -10 5 lines 1 year • CAD system 10 5 -10 6 lines 2 years • airline reservations 10 6 + lines 3 years Software makers must keep systems running for at least 5-10 years to recover investment and make a profit.
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© D.Lowther 2001, T. Arbel 2003 Operating System Design General principle: User processes communicate with the operating system, operating system communicates with hardware. Implications: User processes are forbidden to access hardware directly.
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© D.Lowther 2001, T. Arbel 2003 Process • What is a process? • The application you see (word processor or spreadsheet or game) is, indeed, a process, but that application may cause several other processes to begin, for tasks like communications with other devices or other computers. • There are also numerous processes that run without giving you direct evidence that they ever exist.
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© D.Lowther 2001, T. Arbel 2003 Process • A process, then, is software that performs some action and can be controlled -- – by a user, – by other applications – or by the operating system.
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© D.Lowther 2001, T. Arbel 2003 Operating System Design User processes can tell characteristics of operating system, but not of the machine. They deal with a virtual machine . All conflicts between processes are handled by the operating system. Multiple processes run independently and only communicate with the operating system.
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© D.Lowther 2001, T. Arbel 2003 Layered design – Each layer only communicates with the next inner and outer layers. – Users only see the outer layer or shell. – Hardware only "sees" the innermost layer. User Hard- ware System Kernel User Interface
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© D.Lowther 2001, T. Arbel 2003 Virtual Machines versus Real Machines • Differences: – Input/Output: • The I/O capabilities of the actual hardware may be very complicated; the operating system provides the user with simpler to use I/O capabilities. – Memory
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This note was uploaded on 11/22/2010 for the course ECSE ECSE 322 taught by Professor Lowther during the Winter '04 term at McGill.

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operating systems - Operating Systems D.Lowther 2001, T....

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