Organization of the file system
ASCII files contain text strings that can be printed, viewed on the screen or
edit ordinary text editor.
Another type of binary files-files, means that this is not ASCII files. Usually
they have some internal structure. For example, workable Unix file has five
sections: header, text, data, and symbolic bits reallokatsii table. OS performs
file only if it has the desired format. Another example might be a binary file
backup.
Typing files is not too strict.
Normally, applications, working with files, file type to recognize his behalf in
accordance with generally accepted agreements. For example, files with the
extensions. C,. Pas,. Txt-ASCII files, files with the extensions. Exe-,
executable files with the extensions. Obj,. Zip-binary, etc.
Apart from the name of the OS is often linked to each file, and other
information, such as modification date, size, etc. These other characteristics
are called the attributes of the files. The list of attributes may vary from one
operating system to another. It may include: attributes protection, password,
the name of the creator, flags secrecy, arhivnosti, sistemnosti, binarnosti,
type of access, length record, key position, time, date, size, etc.
This information is usually stored in the directory structure (see section
realization directories), or other structures that provide access to the data
file. Access to files In order to use the information stored in files, it should
be read in memory of the computer. There are several ways to access files.
Early OS provide only one-way serial access (model tape). Record OCR in order of
receipt. Current position readers can be returned to the top of the file (rewind).
However, magnetic disks and drums appeared files with direct access (random).
For spetsifitsirovaniya point where must begin reading are used two ways: from
the start, or with the current position, which gives seek operation.
Serial access based on the model of tape and works as a consistent access
devices, as well as direct. This is the most common model. The Organization of
direct access essential for many applications, such as for database management
systems.
Not all systems support both (consistent and direct) access method. Serial
emulate easy access through direct, but the realization of the direct access via
serial would be very inefficient.
In addition to direct and consistent, there are other methods of access.
Typically, they include construction of the index file and based on the direct
access method. To search for records at the outset makes the index, which is the
index to a record.
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