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Logical organization of the file system One of the main tasks of the operating system is to provide the convenience of the user with data stored on the disk. This OS substitute for the physical structure of the data stored some user-friendly logical model. The logical model is materializing in the file system tree directories output on the screen utilities such as Norton Commander or Windows Explorer, the composite character file names, in command of files. The basic element of this model is a file, which, like the file system as a whole, can be characterized as the logical, and physical structure. The aims and objectives of the file system The file is named area of external memory, which can record and from which you can read the data. Files are stored in memory for power from the power supply, usually on magnetic disks. However, there is no rule without exceptions. One such exception is the so-called electronic disk when memory structure created, simulated filesystem. The main purpose of the file listed below. A lasting and secure storage. Sustainability is achieved through the use of storage devices, independent of nutrition, and high reliability is protected access to files and shared by OS software code, in which equipment failures more often than not destroy information stored in files. Share information. The files provide a natural and easy way of sharing information between applications and users from an understandable human character name and permanence stored information and the location of the file. You must have suitable means of files, including cataloguing books, files together in groups, search files on the grounds, a set of commands for creating, modifying and deleting files. The file can be created by one user, and then used most others, the creator of a file or an administrator can define access rights to the other users. These objectives are being realized OS file system. File System (FS) is a part of the operating system, including: all the files on a disk; sets of data structures used to manage files, such as directories of files, file descriptors, tables of free and working space on the disk; complex system software which implements various operations on files, such as the creation, destruction, read, write, and search for naming files. File system allows live set is simple to run it on some abstract object of the file. In doing so programmers do not have to deal with the details of the actual data on the disk buffering data and other low-level problems with long-term data storage devices. All these functions file system assumes. File system allocates disk memory, supports naming files, displays file names to the addresses in the external memory, provides access to the data supports the division, protect and restore files. Thus, the file system plays the role of the intermediate layer, masking the complexity of long-term physical storage of data, and creating programs to a simpler logical model of the warehouse, as well as providing a set of easy to use commands to manipulate files. Tasks to be resolved FS depend on the method of calculation of the overall process. The simplest type is single and FS in odnoprogrammnyh OS, which include, for example, MS-DOS. The main functions in a FS focus on the following objectives: naming files; programming interface for applications; Display the logical model of a file system on the physical organization of data; Sustainability file system crash diet, errors hardware and software. FS complex tasks in operating multiprogrammnyh single OS, which, although designed for one person, but gives him the ability to run multiple processes. One of the first operating systems of this type was the OS / 2. By the above tasks added a new challenge shared file access from multiple processes. A file in this case is a shared resource, and therefore, file systems must address all the problems associated with such resources. In particular, the FS should be provided file locking and parts, prevent races, but dead, harmonization of copies, etc. In multi-system appears another challenge: protecting a user's files from unauthorized access another user. More complex functions are FS, which operates a network OS. This topic is discussed in the last chapter of the book devoted to the management of network resources. File Types File systems supported several functionally different types of files, which typically includes regular files, files directories, special files, named conveyor displayed in the memory files, and others. Normal files, or files that contain the arbitrary nature of records in the user or which formed as a result of system and user programs. Most modern operating systems (such as UNIX, Windows, OS / 2) does not limit or control the content and structure of conventional file. The content of the file is determined by conventional application, which works with him. For example, a word processor text files consisting of a string of characters represented in any code. This may be documents, source code programs, etc. The text files can be read on screen or printed on the printer. Binary files are not using codes characters, they often have complex internal structure, such as executable code program, or archive file. All operating systems must be able to recognize at least one type of file their own executable files. The directory is a special type of files that contain background information on the systematic collection of files, grouped by users on any of the informal (for example, in one group together files containing documents of a treaty, or the files of a software package). Many operating systems in the directory might include files of any type, including other directories, thus formed tree structure, easy to find. Catalogs establish consistency between filenames and characteristics of the file system for the management of files. Among these characteristics are, in particular, information (or a pointer to another structure containing the data) on the type and location of the file on disk, file access rights and the date of its creation and modification. In all other respects, file system directories treated as ordinary files. Special files is a sham files associated with the I / O devices, which are used for unification of access to files and external devices. Special files allow the user to perform I / O operations through conventional team record in the file or read from the file. These commands are processed first program file system, and then at some point query converted operating system commands control of the device. Modern file systems support and other types of files, such as symbolic links, named conveyor displayed in the memory files. They will be considered at a later date. Hierarchical structure of the file system Users looking to file for a symbolic name. However, the ability of human memory limit the number of names to which you can apply for the name. Hierarchical organizations namespaces significantly expand those limits. That is why most file systems is a hierarchical structure in which the levels established by the fact that lower-level directory can enter
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