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Organization of the file system

All computer applications require storing and updating information. Possibilities of RAM for data storage is limited. First, the memory is usually loses its contents after power, and secondly, the volume of data often exceeds its capacity. Moreover, it is desirable to have information in a non processes. Therefore adopted store data on external media (usually drives), in units called files. Most computer systems provided to external memory (secondary), high capacity, which can store huge amounts of data. However, the characteristics of access to such devices differ significantly from access to the basic characteristics of memory. To improve efficiency in the use of these devices have been developed for specific data structures and algorithms. Files from a user's perspective Introduction Background data management systems for external memory begins with the tapes yet, but today they have become with the advent of magnetic disks. Until then, each application itself to tackle the problem of naming and structuring data in the external memory. It is difficult to maintain records of several external storage media permanently stored information. The Historical step was the move to centralized management systems files. The file management system assumes the allocation of external memory, display file names in the address of the external memory and access to data. File system is part of the operating system, the appointment of which is to organize effective work with the data stored in external memory and the user interface is convenient when working with these data. Organize storage of information on a magnetic disk is not easy. This requires a good knowledge of the device controller disc features his work registers i.t. e. (usually this is the system I / O component of the OS, called the driver disk). To save the user from the complexities of computer equipment and interaction with fashion was clear abstract model of a file system. Operation record or reading the file conceptually simpler than low-level operation with the device. The basic idea of using external memory is as follows. OS divides it into fixed-size blocks, such as 4096 bytes. From the point of view of each user's file consists of a set of individual elements, called records (for example, the characteristics of a facility). Each file stored as a sequence of blocks (not necessarily adjacent); every integer unit keeps records. In some OS (MS-DOS) address blocks containing data file can be organized into a coherent list and made into a separate table in the memory. In other operating system (Unix), address file data blocks are stored in a separate external memory unit (so-called index or index node). This admission is called indexation and is the most common for applications that require random access to records files. The index file is a list of items, each of which contains a number of blocks in the file and an indication of the location of the block. In modern OS files unstructured usually a sequence of bytes (length record equals 1) and reading the next byte
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