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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

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

File Types
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File Types

Many operating systems support many types of files. UNIX and Windows, for instance, have regular files and directories. UNIX also has character and block special files. Regular files are the ones that contain user information. All the files of FILES Figure 2,

FILES
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FILES

Files are an abstraction mechanism. They provide a way to store information on the disk and read it back later. This must be done in such a way as to shield the user from the details of how and where the information is stored, and how the disks really work.

file-systems
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file-systems

All computer applications need to store and get back information. While a process is running, it can store a limited amount of information within its own address space. On the other hand, the storage capacity is restricted to the size of the virtual address space. For some

Segmentation with Paging: The Intel Pentium
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Segmentation with Paging: The Intel Pentium

In many ways, the virtual memory on the Pentium resembles that of MULTICS, including the presence of both segmentation and paging. Whereas MULTICS has 256K independent segments, each up to 64K 36-bit words, the Pentium has 16K independent segments, each holding

Segmentation with Paging: MULTICS
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Segmentation with Paging: MULTICS

If the segments are large, it may be inconvenient, or even impossible, to keep them in main memory in their entirety. This leads to the idea of paging them, so that only those pages that are really required have to be around. Many significant systems have supported paged

SEGMENTATION
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SEGMENTATION

The virtual memory discussed so far is one-dimensional because the virtual addresses go from 0 to some maximum address, one address after another. For various problems, having two or more separate virtual address spaces may be much better than having only one. For

Separation of Policy and Mechanism
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Separation of Policy and Mechanism

An important tool for managing the complexity of any system is to separate policy from mechanism. This principle can be applied to memory management by having most of the memory manager run as a user-level process. Such a separation was first done in Mach (Young et al.,

Backing Store
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Backing Store

In our study of page replacement algorithms, we saw how a page is chosen for removal. We have not said much about where on the disk it is put when it is paged out. Let us now explain some of the problems related to disk management. The simplest algorithm for allocating page