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Organization of the file system

Assume that there is a large file containing a range of information about students, consisting of records with several fields, and a challenge in organizing quick search on one of the fields, such as the names of a student. Method of allocating disk space with the help of index nodes used in a number of operating system (Unix and a number of others, the following chapter) can serve as an example to other organizations index. In this case, OS uses a tree-organizing clusters, in which blocks that make up the file are tree leaves, and each internal node contains pointers to the file blocks are many. For large index files can be very large. In this case, create an index for the index file (intermediate level of blocks or clusters of indirect addressing). Operation to the files. The operating system must make available to the user a set of operations to work with files sold through system calls. More often than not, when dealing with the file the user is not one but several operations. First, the need to find a data file and its attributes to the symbolic name of his second, take the necessary attributes of the file in the reserved area of RAM and analyze the user to perform the required operation. Then perform the operation, followed by the release of the data file area occupied by memory. Consider the example of the basic file operations Unix OS: ? Create. Creating a file that contains no data. The essence of the call-announce that the file exists and apply a number of attributes. ? Delete. Deleting a file and the release of his employee disk space. ? Open. Before using a file should open it. The purpose of the call system to allow the system to analyze the attributes of the file and check access to the file, as well as take into RAM blocks list of the file for quick access to its data. ? Close. If the work is completed with the file, its attributes and address blocks on the disk are no longer required. In this case, the file must be closed to free up space in the interior tables file system. ? Seek. Enables specify the location of the file where there will be reading (or record) data, that is to ask the current position. ? Read. Reading data from the file. This usually happens with the current position. Users should ask volume readable data buffer and provide for them. ? Write. Writing data to a file from the current position. If the current position is at the end of a file, its size is increased, otherwise entry is a place available data, which thus lost. ? Get attributes. Provides processes they need information on the attributes of a file. As an example, make utility, which uses information on the last modification of files. ? Set attributes. Enables user to install some attributes. The most obvious example is the installation of a regime of access to the file.
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