Process

OPERATING SYSTEM CONCEPTS - PROCESSES
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OPERATING SYSTEM CONCEPTS - PROCESSES

The majority of operating systems provide certain essential concepts and abstractions such as processes, address spaces, and files that are most important to understanding them. In

Address Spaces
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Address Spaces

Every computer has some main memory that it uses to hold executing programs. In a very simple operating system, only one program at a time is in memory. To run a second program, the first o

Files
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Files

Another key concept supported by virtually all operating systems is the file system. As noted before, the most important function of the operating system is to hide the peculiarities of the

Miscellaneous System Calls
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Miscellaneous System Calls

Various other system calls exist as well. We will consider just four of them here. The chdir call changes the current working directory. After the call

The Windows Win32 API
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The Windows Win32 API

We have, so far, focused mostly on UNIX. Now it is time to briefly describe Windows. Windows and UNIX differ in a primary way in their respective programming models. A UNIX program contains code that does

PROCESSES AND THREADS
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PROCESSES AND THREADS

We are now about to start a detailed stu`dy of how operating systems are designed and created. The most essential concept in any operating system is the process: an abstraction of

The Process Model
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The Process Model

In this model, all the runnable software on the computer, sometimes including the operating system, is organized into a number of sequential processes, or just processes for short. A process is just an example of an executing program, including the current values of the program

Process Termination
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Process Termination

After a process has been created, it starts running and performs whatever its job is. However, nothing lasts forever, not even processes. Sooner or later the new process will end, generally due to one of the following conditions:

Process Hierarchies
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Process Hierarchies

In some systems, when a process creates another process, the parent process and child process continue to be connected in certain ways. The child process can itself create more processes, forming a process hierarchy. Note that unlike plants and animals that use sexual

Process States
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Process States

Although each process is an independent entity, with its own program counter and internal state, processes sometimes have to interact with other processes. One process may produce some output that another process uses as input. In the shell command

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