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Formatting FAT 12 is usually only for small discs of no more than 16 MB to use clusters of more than 4 KB. For the same reason, it is considered that the FAT 16 drive with the best for no more than 512 megabytes, and large disk best FAT32, which can use 4 KB clusters with disks up to 8 GB and only drive more began using 8 16 and 32 KB. The maximum size of the FAT 16 restricted 4 GB, this volume is 65,536 clusters of 64 KB each, and the maximum size FAT32 virtually unlimited-232 clusters of 32 KB. Table FAT in fixed razryadnosti indicators index is a variable amount depending on the volume of data on the disk. Deleting a file of the FAT file system in the first bit of a directory entry recorded a special sign indicating that the entry is free, and all indications index file is stored sign free "cluster". Other data in a directory entry, including the number of the first cluster file remain intact, leaving chances to restore mistakenly deleted files. There are many tools to restore deleted files FAT outlet user names deleted files missing from the first character name, clobbered after the release notes. Obviously, the well can be restored only files that are located in consecutive disk clusters, as in the absence of a coherent list of randomly located identify cluster remote file is not possible (without examining the contents of clusters performed by "manually"). Backup FAT always synchronized with the primary copy of any transaction files, so the backup can be used to cancel the malfunctioning of the user unwell in terms of the system is correct. Backup can be used only when the main memory sectors are physically damaged and not read. FAT is used in the method of storing contact information on the files is not very reliable, with the gap list of indicators index in one place, for example because of the failure in the software code OS because of the external electromagnetic disturbances, loss of information on all subsequent file clusters. FAT12 file systems FAT16 and operated with filenames consisting of 12 characters on the scheme of "8.3". In version FAT16 Windows NT was introduced a new type of directory entry-long "name", which allows the use of names to 255 characters in length, with each character long name stored in a byte Unicode. Name of scheme "8.3", now called short (not to confuse it with a simple filename, also sometimes called short), still stored in 12-byte file name field in a directory entry, a long name placed on the portion 13 characters in one or more records, following directly behind the main directory listing. Every character in Unicode format encoded by two bytes, and 13 characters occupy 26 bytes, and the remaining 6 disqualified under proprietary information. Thus there are two of the file name is short for compatibility with older applications, not understanding the long names in Unicode, and the long, easy-to-use name. FAT32 file system also supports the short and long names. FAT12 file systems FAT16, and received a large spread through the use of operating systems MS-DOS and Windows 3.x, the largest operating system first decade era of personal computers. For this reason, these filesystems are supported today, and other operating systems such as UNIX, OS / 2, Windows NT/2000, and Windows 95/98. However, because of ever-increasing volumes of hard disks, as well as increasing demands for reliability, these file systems quickly pushed out as FAT32 system, first appeared in Windows 95 OSR2, and other types of file systems. The physical organization and s5 ufs Filesystems s5 (won title of System V, descent named several versions of UNIX operating system developed at Bell Labs, the company AT & T) and ufs (UNIX File System) used very close to the physical model. This is not surprising, as the system is the development of ufs s5. Filesystem ufs empowers s5 to support large disks and files, as well as increase its reliability. ATTENTION In this section, instead of the term "cluster" will use the term "unit" as per UNIX file systems. Location file system s5 disk illustrates rice. 7.15. Section disk where the file system is divided into four areas: boot block; super (superblock) contains the most general information about the file system: the size of the file system, the size of the field descriptor index number descriptor index, a list of free blocks and the list of free index descriptors, and other administrative information; area index descriptors (inode list), the order in which the index descriptors which corresponds to their rooms; area data, which are as ordinary files, files and directories, including root; special files in the file system only records in the catalog and index descriptors special format, but the location of the data is not. The main physical characteristics of the file system is s5 office filename of the characteristics stored in a separate structure, called descriptor index (inode). S5 in the descriptor index size is 64 bytes and contains data on the type of file, the address information, file access privileges, and some other information: ID holder file; type; the file may be conventional file, directory, a special file, as well as conveyor or symbolic links; access to the file; Provisional characteristics: the last modification of files, the last of the file, the last modification index descriptor; The number of references to this descriptor index equal to the number of aliases file; targeted information (address structure considered above under "physical organization and address file"); The file size in bytes. Each descriptor index number is, who is a unique file name. Index descriptors are located in a special area of the disk in strict accordance with their numbers. Match complete character filenames and their unique name with a hierarchical directory. The system maintains a list of rooms free index descriptors. When you create a file number allocated to him from the list, and the destruction of a file descriptor index number of returns to the list. Writing on file in the directory consists of only two fields: character file name and index number descriptor. For example, in Fig. 7.16 is the information contained in the directory / user. Filesystem not impose special restrictions on the size of the root, because it is located in the area and can grow as a normal file. Access to the file is through the consistent view of the supply chain catalogues of the full file name, and their index descriptors. Search ends after all the characteristics of the index specified file descriptor.
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