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Graf, describing the hierarchy of folders can be wood or network. Catalogs are
trees, if a file is allowed to enter only in the same directory (see Figure 7.3,
b), and network - if the file can include just a few folders (Figure 7.3 in).
For example, MS-DOS and Windows directories form a tree-like structure and UNIX-network.
In the tree structure of each file is a sheet. Catalog highest level is called
the root directory, or root (root). When an organization exempt from the user
remember the names of all files, it is about to submit, which group can be
assigned a file to by the consistent view directories to locate him.
Hierarchical structure suitable for multiplayer work: each user with their files
located in a directory or directories poddereve, but all the files in the system
logically linked. Private case hierarchy is a single organization, which
includes all the files in one folder (see Figure 7.3, a). Filenames All types of
files are symbolic names. In organized hierarchical file systems are usually
used three types of name-files: simple, and relative components. A simple, or
short, symbolic name identifies the file in a single directory. Simple names
assign files users and programmers, but they must take into account the
limitations OS as a range of characters, and character name. Until relatively
recently, these borders were very narrow. For example, the popular file system
FAT length names restricted scheme 8.3 (8 characters proper name, 3-character
extension name), and the file system s5 supported many versions of UNIX OS, the
mere symbolic name could not contain more than 14 characters. However, the user
is much easier to work with long names, as they provide a simple name files
easily, clearly pointing that is contained in the file. So modern file systems,
as well as enhanced versions of existing file systems are usually simple
symbolic support for long file names. For example, the file sie- topic NTFS
and FAT32 members of the Windows NT operating system, the file name can contain
up to 255 characters. Examples of simple file names and directories: quest_ul.doc
task-entran.exe annex 254L SS at the Russian yazyke.doc installable filesystem
manager.doc In hierarchical file systems different files allowed to have the
same simple symbolic names on the condition that they belong to different
directories. So here is a scheme of "one simple file-name". For odpoznachnoy
identification file in the system used by so-called full name. The full name is
a simple conversation character names of all directories crossing path from the
root to the file. Thus, the full name is a composite, which are simple names
separated by separator in the OS. Often used as a separator or back straight
away, with no state name root. Fig. 7.3, a two files are simple main.exe name,
but their constituent names / depart / main. ehe and / user / anna / main.exe
different. In between tree file system and file its full name is mutually clear
line "one file, one full name." In the file systems of the network structure,
the file may consist of multiple directories, and therefore have several full
names; Here true that "one file, many proper names." In both cases, file clearly
identifies full name. The file may be identified relative to the name. The
relative file name is determined by the notion of "current directory." For each
user every time one of the catalog file system is ongoing, and this directory is
selected by the user teammates OS. File system captures the current directory
name, then use it as a complement to the relative names for the full file name
of education. Using relative names user identifies the file names chain
catalogues crossing route from the current directory to the file. For example,
if the current directory is the directory / user, the relative file name / user
/ anna / main.exe as follows: anna / main.exe. Some operating systems are
allowed to give the same file some simple names, which can be interpreted as an
alias. In this case, as in a network structure, "a line single file, many proper
names, because each simple filename with at least one full name. While full name
clearly identifies the file, the operating system easier to work with the file
if the files and their names are mutually clear line. To this end, it shall file
a unique name, so that the ratio of true "one file, one unique name." Unique
name coexists with one or more character names assigned to the file by users or
applications. The unique name is a numeric identifier, and is for the operating
system. An example of such a unique filename is the descriptor index number UNIX.
Mounting Generally, a computer system can have multiple disk devices. Even a
typical personal computer usually has a hard disk drive, a floppy disk drive in
and drive to the CD. Powerful same computers are usually equipped with a large
number of disk drives that are installed packages discs. Indeed, even one
physical device through the operating system can be presented in several logical
devices, in particular by disk space split into sections. The question is how to
store files in the system with few external memory devices? The first is that in
each of the devices running standalone file system, the files that are on the
same device, describes the tree of directories is not connected with the trees
of directories on other devices. In this case a unique identification file for
the user, along with a symbolic name of the file to indicate the logical
identifier devices. An example of such an autonomous existence file system is MS-DOS
operating system, which includes the full file name ID logical drive letter.
Thus, when the file located on the A drive, the user must specify the name of
the disk: A: \ privat \ letter \ uni \ let1.doc1. 1 In practice, increasingly
used the relative form of naming, which does not include the name of the drive
and chain have top-level directories specified default. Another option is the
organization file storage, in which the user can combine file systems located on
different devices in a single file system, described a single directory tree.
The operation is called moptirovaniem. Consider how the operation in the case of
UNIX OS. Among all available in the logical disk devices operating system
provides a device called a system. May has two file systems located on different
logical drives (Figure 7.4), with one disk is a system. File system, based on a
system disk, a root. To contact hierarchies files in the root file system chosen
some existing directory, in this example, the directory man. After mount folder
man becomes chrooted second file system. Through this directory is mounted file
system as a subfolder connected to a common tree (Figure 7.5). After mounting a
common file system for the user no logical difference between root and mounted
file systems, in particular the naming of files is the same as if it were from
the very beginning was united.
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