FAT16 supports a maximum of 65, clusters per volume. The following table lists FAT16 size limits. A FAT32 volume must have a minimum of 65, clusters. The following table lists FAT32 size limits. In this post, I am going to talk about the 10 computer networking concepts that every professional should master. I will also include links to the main articles of each concept.
This theoretical model explains how networks behave within an orderly, seven-layered Skip to content FAT stands for File Allocation Table, is specifically, a table maintained on a hard disk by MS-DOS and Microsoft Windows operating systems that acts as a table of contents, showing where directories and files are stored on the disk.
Back to Index. The second file, File2. A small file, File3. In each case, the folder structure points to the first cluster of the file. Instead, the FAT has to be scanned as an array to find free clusters, which can lead to performance penalties with large disks. In fact, seeking for files in large subdirectories or computing the free disk space on FAT volumes is one of the most resource intensive operations, as it requires reading the directory tables or even the entire FAT linearly.
Since the total amount of clusters and the size of their entries in the FAT was still small on FAT12 and FAT16 volumes, this could still be tolerated on FAT12 and FAT16 volumes most of the time, considering that the introduction of more sophisticated disk structures would have also increased the complexity and memory footprint of real-mode operating systems with their minimum total memory requirements of KB or less such as with DOS for which FAT has been designed and optimized originally.
With the introduction of FAT32, long seek and scan times became more apparent, particularly on very large volumes. A possible justification suggested by Microsoft's Raymond Chen for limiting the maximum size of FAT32 partitions created on Windows was the time required to perform a " DIR " operation, which always displays the free disk space as the last line.
FAT32 therefore introduced a special file system information sector where the previously computed amount of free space is preserved over power cycles, so that the free space counter needs to be recalculated only when a removable FAT32 formatted medium gets ejected without first unmounting it or if the system is switched off without properly shutting down the operating system, a problem mostly visible with pre- ATX -style PCs, on plain DOS systems and some battery-powered consumer products.
With the huge cluster sizes 16 KB, 32 KB, 64 KB forced by larger FAT partitions, internal fragmentation in form of disk space waste by file slack due to cluster overhang as files are rarely exact multiples of cluster size starts to be a problem as well, especially when there are a great many small files.
Various optimizations and tweaks to the implementation of FAT file system drivers, block device drivers and disk tools have been devised to overcome most of the performance bottlenecks in the file system's inherit design without having to change the layout of the on-disk structures. They can be divided into on-line and off-line methods and work by trying to avoid fragmentation in the file system in the first place, deploying methods to better cope with existing fragmentation, and by reordering and optimizing the on-disk structures.
With optimizations in place, the performance on FAT volumes can often reach that of more sophisticated file systems in practical scenarios, while at the same time retaining the advantage of being accessible even on very small or old systems.
DOS 3. This not only helps to maintain the integrity of deleted files for as long as possible but also speeds up file allocations and avoids fragmentation, since never before allocated disk space is always unfragmented. DOS accomplishes this by keeping a pointer to the last allocated cluster on each mounted volume in memory and starts searching for free space from this location upwards instead of at the beginning of the FAT, as it was still done by DOS 2.
This mechanism is defeated, however, if an application often deletes and recreates temporary files as the operating system would then try to maintain the integrity of void data effectively causing more fragmentation in the end.
Additionally, directory entries of deleted files will be marked 0xE5 since DOS 3. Since DOS 3. Before DOS 5. Windows NT will allocate disk space to files on FAT in advance, selecting large contiguous areas, but in case of a failure, files which were being appended will appear larger than they were ever written into, with a lot of random data at the end.
Other high-level mechanisms may read in and process larger parts or the complete FAT on startup or on demand when needed and dynamically build up in-memory tree representations of the volume's file structures different from the on-disk structures.
This may, on volumes with many free clusters, occupy even less memory than an image of the FAT itself. In particular on highly fragmented or filled volumes, seeks become much faster than with linear scans over the actual FAT, even if an image of the FAT would be stored in memory. Also, operating on the logically high level of files and cluster-chains instead of on sector or track level, it becomes possible to avoid some degree of file fragmentation in the first place or to carry out local file defragmentation and reordering of directory entries based on their names or access patterns in the background.
Such features became available later. Later DOS versions also provided built-in support for look-ahead sector buffering and came with dynamically loadable disk caching programs working on physical or logical sector level, often utilizing EMS or XMS memory and sometimes providing adaptive caching strategies or even run in protected mode through DPMS or Cloaking to increase performance by gaining direct access to the cached data in linear memory rather than through conventional DOS APIs.
Write-behind caching was often not enabled by default with Microsoft software if present given the problem of data loss in case of a power failure or crash, made easier by the lack of hardware protection between applications and the system. Microsoft applied for, and was granted, a series of patents for key parts of the FAT file system in the mids. Being almost universally compatible and well-understood, FAT is frequently chosen as an interchange format for flash media used in digital cameras and PDAs.
All four pertain to long-filename extensions to FAT first seen in Windows 95 :. Microsoft is not the only company to have applied for patents for parts of the FAT file system. Other patents affecting FAT include:. The USPTO acknowledged that the evidence raised "substantial new question[s] of patentability," and opened an investigation into the validity of Microsoft's FAT patents. On the USPTO announced that, following the re-examination process, it had again rejected all claims of patent 5,,, and it additionally found U.
Patent 5,, invalid on the grounds that the patent had incorrect assignees. However, on the USPTO ruled that features of Microsoft's implementation of the FAT system were "novel and non-obvious", reversing both earlier non-final decisions.
In February , Microsoft filed a patent infringement lawsuit against TomTom alleging that the device maker's products infringe on patents related to FAT32 file system. As some TomTom products are based on Linux , this marked the first time that Microsoft tried to enforce its patents against the Linux platform.
In October , Microsoft filed a patent infringement lawsuit against Motorola alleging several patents including two of the FAT32 file system patents were not licensed for use in the Android operating system. Chat WhatsApp.
Main article: exFAT. Microsoft TechNet. Retrieved TXT, draft revision 2 [1], [2]. Last access dates are turned off for all drives when your computer is started in safe mode, and are not maintained for floppy disks by default. Standard ECMA 2nd ed.
ISO catalogue. ISO Reynolds, Dennis R. Adler, Ralph A. Lipe, Ray D. Pedrizetti, Jeffrey T. Parsons, Rasipuram V. Arun US Patent Microsoft Press.
ISBN Michels, Jim Kyle Undocumented DOS. Addison Wesley, second edition. DosMan Drivel. Hard Drive. ISBN , p. Berlin: Springer. In fact, the number is less than this, since h and h are not used and FF0h to FFFh are reserved or used for other purposes, leaving h to FEFh 2 to as the range of possible clusters. DOS Internals. Addison Wesley.
Wyse DOS 3. Document Q [4]. Upgrading Pre Document Q [5]. Microsoft Help and Support. December 16, Microsoft Knowledge Base. Implementation of extended attributes on the FAT file system. Also the opposite could [ Both situations [ The Linux Kernel archives.
Xbox-Linux project. The DISK. Comment: The author mentions that DOS 4. Reschke Sybex, 4th edition, 12th batch. Microsoft press. User-Prompt Guides, UK [15]. DEW Associates Corporation. ZIP collection maintained up to and distributed on many sites at the time. TXT file. The FDOS. EQU file in the machine readable source kit has equates for the corresponding directory entries. The version [ IFS Wiki and Sources. Printed in the UK, August Caldera Part No. Various non operating systems take different actions if these bits are turned on [ After [ IBM document R, [23].
Linux man page. Microsoft Systems Journal. This particular text file has a number of OCR errors; e. TechNet Magazine July Intellectual Property Licensing. Public Patent Foundation. CNET News. The Register. Retrieved 2 April File systems.
Optical disc. Standards of Ecma International. ISO standards. See also All articles with prefix "ISO". From Wikipedia, the free encyclopedia. Online Registration. Regular Lectures. Malang -- Jawa Timur :. Bandung -- Jawa Barat :. Show all in Bandung Chatting dengan Staf :.
Select Language :. Prev file command. File attribute Next. Linked list. Contents 1 Overview 1. Data Region for files and directories Jump instruction. If the boot sector has a valid signature residing in the last two bytes of the boot sector tested by most boot loaders residing in the System BIOS or the MBR and this volume is booted from, the prior boot loader will pass execution to this entry point with certain register values, and the jump instruction will then skip past the rest of the non-executable header.
See Volume Boot Record. OEM Name padded with spaces 0x This value determines in which system the disk was formatted. Some vendors store licensing info or access keys in this entry.
File system and operating system specific boot code; often starts immediately behind [E]BPB, but sometimes additional "private" boot loader data is stored between the end of the [E]BPB and the start of the boot code.
Physical drive number only in DOS 3. Then you can tell that the FAT file system is named for its method of organization - the file allocation table. It is a file system invented by Microsoft in for disk management , and it is used as the default file system in Windows before the release of NTFS. The FAT file system roughly divides the space of the logical disk into four parts, which are boot sector , file allocation table area, root directory area and data area.
Boot sector: It is also called reserved sector, and located in the first part. It includes: the boot loader code needed by the operating system to start computer, the partition table of the main boot record mbr which describes how the drive is organized, and the BIOS parameter block BPB which describes the physical outline of the data storage volume. FAT area: This section usually contains two copies of the file allocation table for redundancy checking and specifying how to allocate clusters.
Root directory area: This area is a directory table containing information about directories and files.
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