CS3733OSExamReview - CS 3733 Operating Systems First...

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CS 3733 Operating Systems First Midterm Exam Review: Spring 2006 This will be a closed book exam. Listed here are the major topics covered on the midterm exam. 1. Introduction: what is an operating system? a. Buffering - A method of overlapping the I/O of a job with its execution. After data has been read and while the CPU starts execution, the input device is instructed to begin the next input immediately so that it is in memory when it is requested. b. Spooling - S imultaneous P eripheral O peration O n- L ine Using a disk or similar device as a large buffer, for reading as far ahead as possible on input devices or storing output files until the output device (or devices) are ready for them. Buffering overlaps the I/O of a job with its own computation. Spooling overlaps the I/O of a job with the computation of all other jobs. Spooling can be used to provide a job pool. c. Multiprogramming - Several jobs from the job pool are kept in memory. The OS picks and begins execution of one of these jobs. If the job needs to wait for an I/O device the OS switches to executing another job. When that job needs to wait the OS switches to another job. The CPU therefore can be kept busy more of the time. We say these jobs are being run concurrently. This is an aspect of operating systems that adds much of its complexity. d. Time sharing - This is an extension of multiprogramming. No job is allowed to use the CPU for more than a certain time, called the quantum. A timer is set when a job enters the CPU. If the timer expires before the job request I/O, another job is chosen for execution. If the quantum is small compared to a human time scale, it seems as if many jobs are running simultaneously. This allows for a high degree of interaction between the user and the computer without the associated inefficiency as the CPU waits for the user to push a key. Similar to when only one person could use a computer at a time. Note: if there is only one CPU, at most one user job can be running at any time.
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e. D istributed systems - There are two schemes for using several physical processors for computation. In tightly coupled systems processors share memory and a clock. In loosely coupled systems each processor has its own local memory but they share communication lines. These loosely coupled systems are referred to as distributed systems. Here are some advantages: i. Resource sharing --- files, printers, software ii. Computation Speed Up iii. A computation may be broken into parts, each done on a different processor. iv. Reliability --- If one processor goes down, the rest will still be able to do useful work. v. Communication --- Mail and the Web 2. Processes a. Process state b. Process control block – A process in an operating system is represented by a data structure known as a process control block (PCB) or process descriptor. The PCB contains important information about the specific process including: The current state of the process i.e., whether it is ready, running, waiting, or whatever.
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This note was uploaded on 09/21/2009 for the course CS 3733 taught by Professor Staff during the Spring '08 term at The University of Texas at San Antonio- San Antonio.

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CS3733OSExamReview - CS 3733 Operating Systems First...

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