System Call

The Classical Thread Model
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The Classical Thread Model

Now that we have seen why threads might be helpful and how they can be used, let us examine the idea a bit more closely. The process model is based on two independent ideas: resource grouping and execution. Often it is beneficial to separate them; this is where threads

Hybrid Implementations / Scheduler Activations
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Hybrid Implementations / Scheduler Activations

Different ways have been considered to try to unite the benefits of user-level threads with kernel-level threads. One way is use kernel-level threads and then multiplex user-level threads onto some or all of the kernel threads, as shown in the following figure. When this approach is

Making Single-Threaded Code Multithreaded
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Making Single-Threaded Code Multithreaded

Many current programs were written for single-threaded processes. Converting these to multithreading is much complicated than it may at first appear. Below we will study just a few of the drawbacks.

SCHEDULING
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SCHEDULING

When a computer is multiprogrammed, it often has multiple processes or threads competing for the CPU simultaneously. This situation happens whenever two or more of them are in the ready state at the same time. If only one CPU is available, a choice has to be made which

Separate Instruction and Data Spaces / Shared Pages
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Separate Instruction and Data Spaces / Shared Pages

The majority of computers have a single address space that holds both programs and data, as shown in Figure 1(a). If this address space is large enough, everything works fine. On the other hand, it is often too small, forcing programmers to stand on their heads to fit everything

File Attributes
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File Attributes

Every file has a name and its data. Moreover, all operating systems associate other information with each file, for instance, the date and time the file was last modified and the file's size. We will call these extra items the file's attributes. Some people call them metadata. The list of

An Example Program Using File System Calls
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An Example Program Using File System Calls

In this section we will consider a simple UNIX program that copies one file from its source file to a destination file. It is listed in Figure 1. The program has minimal functionality and even worse error reporting, but it gives a reasonable idea of how some of the system calls related to

DIRECTORIES
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DIRECTORIES

To keep track of files, file systems generally have directories or folders, which in many systems are themselves files. Now we will discuss directories, their organization, their properties, and the operations that can be performed on them.

PRINCIPLES OF I/O SOFTWARE
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PRINCIPLES OF I/O SOFTWARE

Let us now turn our attention from the I/O hardware to the I/O software. First we will consider the goals of the I/O software and then at the various ways I/O can be done from the point of view of the operating system.

User-Space I/O Software
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User-Space I/O Software

Though most of the I/O software is within the operating system, a small portion of it comprises libraries linked together with user programs, and even whole programs running outside the kernel. System calls, including the I/O system calls, are usually made by library procedures.

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