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Unformatted text preview: vantages:
1. It is difficult to implement because it requires algorithms to support demand
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.
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.
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,
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- Spring '14