Unix

The Third Generation (1965-1980) ICs and Multiprogramming
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The Third Generation (1965-1980) ICs and Multiprogramming

By the early 1960s, the majority of computer manufacturers had two different, incompatible, product lines. On the one hand there were the word-oriented, large-scale scientific computers, such as the 7094, which were used for numerical calculations in science and

Protection
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Protection

Almost all computers contain great amounts of information that users often want to protect and keep confidential. This information may include e-mail, business plans, tax returns, and

System Calls for File Management
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System Calls for File Management

Many system calls relate to the file system. In this section we will look at calls that operate on individual files; in the next one we will study those that involve directories or the file system as a whole.

System Calls for Directory Management
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System Calls for Directory Management

Now we will consider some system calls that relate more to directories or the file system as a whole, rather than just to one particular file as in the previous section. The first two calls, mkdir and rmdir, create and remove

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

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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