In this case all file access operations at operating

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Unformatted text preview: vantages: 1. It is difficult to implement because it requires algorithms to support demand paging. 2. If used carelessly, it may substantially decrease performance instead of increasing performance. This happens when page-fault rate is very high for a process. That is, the process spends more time in swapping out and swapping in of pages than in its execution. FILE MANAGEMENT A file is a collection of related information. Every file has a name, its data, and attributes. The name of a file uniquely identifies it in the system and is used by its users to access it. A file's data is its contents. The contents of a file is a sequence of bits, bytes, lines, or records whose meaning is defined by the file's creator and user. The attributes of a file contain other information about the file such as the date and time of its creation, date and time of last access, date and time of last update, its current size, its protection features (who can access the file and in what way), etc. The list of attributes maintained for a file varies considerably from one system to another. The file management module of an operating system takes care of file-related activities such as structuring, accessing, naming, sharing, and protection of files. In this section we will discuss about the important concepts used for file management in various operating systems. File Structure Files can be structured in many ways. However, the two popular types of file structures used by operating systems are files as unstructured sequence of bytes and files as sequence of fixed-length records. The two types of file structures are briefly described below. Files as Unstructured Sequence of Bytes As shown in Figure 14.16(a), in this case the operating system treats a file as nothing more than byte sequences. That is, all file access operations at operating system level deal with the number of bytes to be read, written or skipped. No interpretation of the bytes is made by the operating system. This type of file structuring scheme provides maximum flexibility, but minimal support. That is, e...
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This document was uploaded on 04/07/2014.

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