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Virtual File Systems
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Virtual File Systems

Several different file systems are in use - often on the same computer - even for the same operating system. A Windows system may have a main NTFS file system, but also a legacy FAT-32 or FAT-16 drive or partition that includes old, but still needed, data and occasionally a

Journaling File Systems
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Journaling File Systems

While log-structured file systems are an interesting idea, they are not extensively used, in part due to their being highly incompatible with existing file systems. However, one of the ideas inherent in them, robustness in the face of failure, can be easily applied to more conventional

Log-Structured File Systems
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Log-Structured File Systems

Changes in technology are putting pressure on current file systems. Particularly, CPUs keep getting faster, disks are becoming much bigger and cheaper (but not much faster), and memories are growing exponentially in size. The one parameter that is not improving by leaps and

Shared Files
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Shared Files

When various users are working together on a project, they often need to share files. As a result, it is often convenient for a shared file to appear simultaneously in different directories belonging to different users. Figure 1 shows the file system of DIRECTORIES Figure 2, again,

Implementing Directories
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Implementing Directories

Before a file can be read, it must be opened. When a file is opened, the operating system uses the path name supplied by the user to locate the directory entry. The directory entry provides the information required to find the disk blocks. Depending on the system, this information

FILE SYSTEM IMPLEMENTATION
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FILE SYSTEM IMPLEMENTATION

Now it is time to turn from the user's view of the file system to the implementor's view. Users are concerned with how files are named, what operations are allowed on them, what the directory tree looks like, and similar interface issues. Implementors are interested in how files and

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.

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,