What is a file?
- In any computer system but especially in personal computers, a file is an
entity of data available to system users (including the system itself and its
application programs) that is capable of being manipulated as an entity
(for example, moved from one file directory to another). The file must have a
unique name within its own directory. Some operating systems and applications
describe files with given formats by giving them a particular file name suffix.
(The file name suffix is also known as a file name extension.) In general, the
suffixes tend to be as descriptive of the formats as they can within the limits
of the number of characters allowed for suffixes by the operating system. In DOS
8+3 characters is allowed for a file name.
Almost all information stored in a computer must be in a file. There are many
different types of files: data files, text files , program files, directory files,
and so on. Different types of files store different types of information.
In a computer, a file system is the way in which files are named and where they
are placed logically for storage and retrieval. The DOS, Windows (95-98-Me, NT-2000-XP),
OS/2, Macintosh, and UNIX-based operating systems all have file systems in which
files are placed somewhere in a hierarchical (tree) structure. A file is placed
in a directory (folder in Windows) or subdirectory at the desired place in the
tree structure.
File systems specify conventions for naming files. These conventions include the
maximum number of characters in a name, which characters can be used, and, in
some systems, how long the file name suffix can be. A file system also includes
a format for specifying the path to a file through the structure of directories.
File systems limit the size of individual files: the newer the operation system
the larger the maximum allowed size.
- In data processing, using an office metaphor, a file is a related collection
of records. For example, you might put the records you have on each of your customers
in a file. In turn, each record would consist of fields for individual data items,
such as customer name, customer number, customer address, and so forth. By providing
the same information in the same fields in each record (so that all records are
consistent), your file will be easily accessible for analysis and manipulation
by a computer program. This use of the term has become somewhat less important
with the advent of the database and its emphasis on the table as a way of collecting
record and field data. In mainframe systems, the term data set is generally synonymous
with file but implies a specific form of organization recognized by a particular
access method. Depending on the operating system, files (and data sets) are contained
within a catalog, directory, or folder.
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