OPERATING SYSTEMS. SYSTEM SOFTWARE IB DP Computer science Standard Level ICS3U. SYSTEM SOFTWARE IB DP Computer science Standard Level ICS3U

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Mervyn McBride
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1 C A N A D I A N I N T E R N A T I O N A L S C H O O L O F H O N G K O N G 6.4 s five of the most important tasks that an operative system performs user interface management control of access to system and files program scheduling and activation efficient resource allocation deadlock detection and error detection user interface management: a receptionist execute whenever no other piece of user or system software is using the processor wait for a user command delivered via the keyboard, mouse, or other input device operating system commands usually request access to hardware resources, software services, or information determine which software package needs to be loaded and put on the schedule for execution 1

2 user interface management: a receptionist command prompt (prior to 1980s) vs. graphical user interface (GUI) GUI is an example of high-level virtual machine created by the operating system control of access to system and files: a security guard prevent unauthorized users from accessing the system and prevent authorized users from doing unauthorized things user login with username and password for added security safeguard the password file that stores all valid user name/password combinations check what operations are permitted program scheduling and activation: a dispatcher an I/O controller frees the processor to do useful work while the I/O operation is being completed keeps a queue of programs that are ready to run 2

3 efficient resource allocation: an efficient expert ensure the operating system is never idled the running history of a program may be a sequence of starts and stops a cycle of execution, waits for I/O operations, waits for the processor, followed again by execution deadlock detection and error: a traffic officer prevent programs or users from attempting operations that cause the computer system to enter a state where it is incapable of doing any further work deadlock means that there is a set of programs, each of which is waiting for an event to occur before it may proceed, but that event can be caused only by another waiting program in the set deadlock detection and error: a traffic officer operating system handle deadlock conditions deadlock prevention: the operating system uses resource allocation algorithms that prevent deadlock from occurring in the first place deadlock recovery: detect deadlock and recover from them when they do occur 3

4 first generation: assemblers and loaders execute instructions with punched cards or tapes one user to one computer second generation: batch operating system programmer surrender a program in batches to an operator for execution many user to one operator to one computer third generation: multiprogrammed operating system user operation codes and privileged operation codes a time-sharing machine introduction of the embedded computers in other devices many user to one computer 4

5 fourth generation: 1980s introduction of the embedded computers in other devices one user to one computer fifth generation: 1990s parallel-processing operating systems recognize opportunities for parallel execution, send the separate tasks to the appropriate processor, and coordinate their concurrent execution distributed computing environment Pg. 315 # 1 Assume that programs spend about 25% of their time waiting for I/O operations to complete. Ifthere are two programs loaded into memory, what is the likelihood that both programs will be blocked waiting for I/O and there will be nothing for the processor to do? What percentage of time will the processor be busy? (This value is called processor utilization.) By how much does processor utilization improve if we have four programs in memory instead of two? 5

6 Pg. 330 # 1 Describe the user interface in other high-technology gy devices commonly found in the home or office, such as a DVD player, audio system, television, copier, or microwave oven. Pick one specific device and discuss how well its interface is designed and how easy it is to use. Does the device use the same techniques as computer system interfaces, such as menus and icons? Pg. 330 # 18 What are some drawbacks in using gpasswords to limit access to a computer system? Describe some other possible ways that an operating system could limit access. In what type of application might these alternative safeguards be appropriate? Pg. 330 # 20 Assume that any individual program spends about 50% of its time waiting for I/O operations to be completed. What percentage of time is the processor doing useful work (called processor utilization) if there are three programs loaded into memory? How many programs should we keep in memory if we want processor utilization to be at least 95%? 6

7 Pg. 330 # 22 Explain why a batch operating system would be totally inadequate to handle such modern applications as airline reservations and automated teller machines. 7

Chapter 6. An Introduction to System Software and Virtual Machines. INVITATION TO Computer Science

Chapter 6. An Introduction to System Software and Virtual Machines. INVITATION TO Computer Science Chapter 6 An Introduction to System Software and Virtual Machines INVITATION TO Computer Science 1 Objectives After studying this chapter, students will be able to: Describe the main categories of system