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Organization of the file system

The first few blocks of addresses file stored directly in the index node, thus the index for small files node keeps all the necessary information, which is copied from disk to memory, at the time of opening the file. For large files from one node addresses index points to a block of indirect addressing. This unit is composed of additional disk blocks. If this is not enough use of indirect addressing double block, which contains the address blocks indirect addressing. If this is not enough and using indirect addressing triple block. This scheme uses Unix (as well as HPFS file system, NTFS, etc.). This approach allows for fixed, relatively small amount of index node support the work with files, which can vary from a few bytes to several gigabytes. It is that for small files used only direct addressing to ensure maximum productivity. Office employed and free disk space. In modern OS used several methods used accounting disk space. Consider the most common. Recognition through the organization bit vector. Often the list of free disk blocks realized in the form of bit vector (or bit map bit vector). Each block is represented by one bit receiving value 0 or 1, depending on whether it is occupied or vacant. For example, 00111100111100011000001 .... The main advantage of this approach is relatively simple and it performs while in the first free block, or n consecutive blocks on the disk. Many computers have the bit manipulation instructions that can be used for this purpose. For example, computers families Intel and Motorola have instructions that in which you can easily locate one single bit in the word. The accounting method described free blocks used in Apple Macintosh. Unfortunately, this technique is effective only if the bit vector is placed entirely in memory, which is possible only for relatively small disks. For example, the size of 1.3 GB disk with blocks of 512 bytes needed in the table size 332 K for the management of free blocks. Integrating communication through the organization list. Another approach - link to the list of all available units, maintaining a pointer to the first free block in a special place of the disk, along keshiruya in memory of this information. The scheme is not always effective. For a list of fingerprinting to be done a lot of hits on the disk. But fortunately we need, as a rule, only the first free block. Sometimes resorting to modify the list cohesive approach, organizing storage addresses n free blocks in the first free block. The first n-1 of these units actually used. The last block is composed of other n blocks. Etc.
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