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| FAT (12-, 16-, and 32-bit) |
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Windows supports the FAT filesystem, and is by far the most simplistic filesystem supported by Windows NT family operating systems, primarily to enable upgrades from other versions of Windows, for compatibility with other operating systems in multiple-boot systems, and as a floppy diskette format, e.g., FAT12 (01h or 0x01 (up to 15MB), 06h or 0x06 (between 32MB - 2GB), 0Bh or 0x0B (up to 2047GB), FAT16 (04h or 0x4) and FAT32.
The name of each FAT format includes a number that indicates the number of bits the format uses to identify clusters on a disk. FAT12’s 12-bit cluster identifier limits the partition to storing a maximum of 212 (4096) clusters. Windows uses cluster sizes from 512-user bytes to 8-user KB in size, which limits a FAT12 volume size to 32MB. Therefore, Windows uses FAT12 as the format for all floppy diskettes, which store up to 1.44MB of data.
FAT16, with a 16-bit cluster identifier, can address 216 (65,536) clusters. For Windows, FAT16 cluster sizes range from 512-user bytes (the sector size) to 64-user KB, which limits FAT16 volume sizes to 4GB. The cluster size Windows uses depends on the size of the volume.
Note: All FAT filesystems formats reserve the first two clusters and the last 16 clusters of a volume, so the number of usable clusters is slightly less than what is theoretically possible.
A FAT volume is divided into several regions. The file allocation table file, which gives the FAT filesystem format its name, has one entry for each cluster on a volume. As the file allocation table is critical to the successful interpretation of a volume’s contents, to protect it, the FAT format maintains two copies of the table so that if a filesystem driver or consistent-checking program (such as chkdsk.exe) cannot access one (because of a bad hard disk drive sector, for example) it can read from the other.
Entries in the file allocation table define file-allocation chains for files and directories, where the links in the chain are indexes to the next cluster of the file’s data. A file’s directory entry stores the starting cluster of the file. The last entry of the file’s allocation chain is the reserved value 0xFFFF (or FFFFh) for FAT16 and 0xFFF (or FFFh) for FAT12. The FAT entries for unused clusters have a value of zero. If a file is fragmented the clusters assigned to it will not be sequential – one reason to keep fragmentation to a minimum for manual data recovery using a hex editor. Regardless, reading a file from a FAT volume can involve tediously reading large portions of a file allocation table to transverse the file’s allocation chains; another reason to keep fragmentation to a minimum.
The root directory of FAT12 and FAT16 volumes are pre-assigned enough space at the start of a volume to store 256 directory entries, which places an upper limit on the number of files and directories that can be stored in the root directory. FAT32 does not have these restriction imposed on it. A FAT directory entry is 32 bytes and stores a file’s name, size, starting cluster and timestamp (last-accessed, created and so forth) information.
FAT32 is the most recently defined FAT-based filesystem format, and it’s included in Win95 OSR2 onwards. FAT32 uses 32-bit cluster identifiers but reserves the high four bits, so in effect it has 28-bit cluster identifiers. Because FAT32 cluster sizes can be as large as 32KB, FAT32 has a theoretical possibility to address 8TB volumes. Although Windows NT family of operating systems works with existing FAT32 volumes of larger sizes (created in other operating systems) it limits new FAT32 volumes to a maximum of 32GBs (by design this is to avert volume instability and format failure near the end of the process that can arise if 32GBs is exceeded). FAT32’s higher potential cluster numbers lets it manage disks more efficiently than FAT16.
Besides the higher limit on cluster numbers, other advantages FAT32 has over FAT12 and FAT16 includes the fact that the FAT12 root directory is not stored at a predefined location on the volume, the root directory does not have an upper limit on its size, and FAT32 stores a second copy of the boot sector for reliability. A limitation FAT32 shares with FAT16 is that the maximum file size is 4GB (2^32 minus one byte) because the directories store file sizes as 32-bit vales. Addition limitations of FAT32 are: clusters cannot be 64KB or greater, a volume must contain at least 65, 527 clusters to use the FAT32 filesystem but no greater than 268,435,445. With the maximum permissible cluster size of 32KB and space for the file allocation table (FAT), this equates to a maximum volume size of 8TB, aforementioned. Some of these limitations relate to FAT32 when installing Windows XP and can be overcome within Windows XP, with some limitations still relevant regardless.
Updating the FAT table is essential and time consuming. If the FAT table is not updated regularly, it can lead to data loss. The reason that updating the FAT table is time consuming is the fact the hard disk drive read heads must be repositioned to the hard disk drive's logical track zero each time the FAT table is updated. There is no organisation to the FAT directory structure, and files are given the first open location on the hard disk drive. In addition, FAT supports only read-only, hidden, system, and archive file attributes.
For a primary partition with a FAT32 volume it is represented within the partition table of the MBR as type 0C.
Note: Unlike the FAT filesystem volume, which contains areas specifically formatted for use by the filesystem, an NTFS volume stores all filesystem data, such as bitmaps and directories, and even the system bootstrap, as ordinary files. Moreover, NTFS guarantees that user data will be consistent and available immediately after a write-through operation or a cache flush, even if the write subsequently fails.
See: File Allocation Table (FAT), Filename, and Terabyte. |
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| Fault Tolerance |
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The ability of computer hardware or software to ensure data integrity when hardware failures occur: to withstand hardware failure. Many levels of tolerance exist, and fault tolerance can be applied to several components and systems. Fault-tolerant features appear in many server operating systems and include mirrored volumes, RAID-5 volumes, and server clusters. RAID stands for Redundant Array of Independent or Inexpensive Disks and is a multi-hard disk drive storage subsystem for data replication.
See: Dynamic Volume. |
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| FDISK.EXE |
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The name of the disk-partitioning program used under several operating systems, e.g., DOS, Windows 9x and Millennium, to create the Master Boot Record (MBR) and allocate partitions for the operating system’s use.
See: Master Boot Record (MBR), and Partition. |
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| File |
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A collection of information kept somewhere other than in random-access memory (RAM) - also known as physical memory, consisting of many blocks of data. With larger files being made up of hundreds if not thousands of blocks of data or more
See, Data, and Sector. |
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| File Allocation Table |
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A filesystem used in DOS and other Windows operating systems to organise and mange files. The file allocation table is a data structure, held near the outer edge of a disk that Windows creates when a volume is formatted using the FAT or FAT32 filesystem. Windows stores information about each file in the file allocation table so that it can retrieve the file later.
In other words, the central structure in the FAT12/16 and FAT32 filesystem is the file allocation table – its position and size can be determined from (defined by) the boot sector. A volume is divided into clusters of one or more sectors. For each cluster an entry is kept in the FAT. For the NTFS filesystem it is the Master File Table (MFT), there is no file allocation table.
A FAT entry in the FAT32 filesystem allows for 32 bits (although only 28 bits are used).
The file allocation table, which gives the FAT filesystem format its name, has one entry for each cluster on a volume. As the file allocation table is critical to the successful interpretation of a volume’s contents, the FAT format maintains two copies of the table so that if a filesystem driver or consistent-checking program (such as Chkdsk) cannot access one (because of a bad hard disk drive sector, for example) it can read from the other.
See: FAT (12-, 16-, and 32-bit), Filesystem, Master File Table (MFT), and NTFS (New Technology File System).
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| File Attribute |
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Information held in the attribute byte of a file’s directory entry.
See: Attribute (Resident & Non-Resident). |
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| Filename |
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The name given to the disk file. Both NTFS and FAT (Windows 9x onwards) allow each filename in a path (directory path) to be as many as 255 characters long. Filenames can contain Unicode characters as well as multiple periods and embedded spaces. However, the FAT filesystem supplied with DOS is limited to the traditional 8 (non-Unicode) characters naming convention for its filename, followed by a period ( . ) or separator and up to a 3-character extension. All filenames must be created with the ASCII character set. The filename must begin with either a number or letter and contain any characters except, (. " / \ [ ] : ; | = ,). The filename cannot contain any spaces and there are certain names that are reserved and converted to uppercased format, e.g., CON, AUX, COM1, COM2, COM3, COM4, LPT1, LPT2, LPT3, PRN, and NUL.
The relationship between 32-bit Windows (Windows) application and DOS Windows applications means that filenames that the Windows subsystem can create on an NTFS volume will not be visible on DOS and 16-bit Windows applications. The group includes filenames longer than the 8.3 format of DOS names, those containing Unicode (international) characters, those with multiple period characters or a beginning period, and those with embedded spaces. When a file is created with such a name, NTFS automatically generates an alternative, DOS-style filename for the file. The DOS filenames are fully functional aliases for the NTFS files and are stored in the same directory as the long filename. The NTFS name and the generated DOS names are stored in the same file record and therefore refer to the same file. The DOS name can be used to open, read from, write to, or copy the file. If a user renames the file using either the long filename or the short filename, the new name replaces both the existing names. If the new name isn’t a valid DOS name, NTFS generates another DOS name for the file. Note: If a file has both an NTFS name and an auto-generated DOS name, a user can delete the file without problems. The filename attribute within the file record of the MFT is always a resident attribute.
Under the registry root key HKEY_CLASS_ROOT – (HKCR) a key exists for every registered filename extension.
Side note: The universal naming convention (UNC) is used for naming files and other resources beginning with two backslashes (\\), indicating that the resource exists on a network computer. UNC names conform to the \\servername\sharename syntax, where servername is the server’s name and sharename is the name of the shared resource. In other words, a shared directory should be in the form of \\servername\sharename. The UNC name of a directory or file can also include the directory path after the sharename, by using the following syntax: \\servername\sharename\directory\filename. Problems can arise if care is not taken to ensure that the directory path does not exceed 32 characters for backup programs, for example.
See: American Standard Code for Information Interchange (ASCII), Attribute (Resident & Non-Resident), FAT (12-, 16-, and 32-bit), File Reference, File Record, Master File Table (MFT), and Universal Naming Convention (UNC). |
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| File Record |
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The row in the Master File Table (MFT) of a NTFS filesystem supported by Windows NT family operating systems corresponding to a particular disk file. The file record is identified by its file reference. NTFS stores files as a collection of attribute/value pairs, one of which is the data it contains, otherwise known as the unnamed data attribute. Other attributes that comprise a file include the filename, timestamp information, and possible additional named data attributes. Each file attribute is stored as a separate stream of bytes within a file – reading and writing attribute streams rather than files themselves. NTFS supplies these attributes operations: create, delete, read (range byte), and write (byte range). The read and write services normally operate on the files unnamed data attribute. However, a caller can specify a different data attribute by using the named data stream syntax. Attributes, in fact, correspond to numeric type-orders, which NTFS uses to order the attributes within a file record. The file attribute in an MFT record are ordered by these types of codes (numerically in ascending order), with some attribute types appearing more than once – if a file has multiple data attributes or multiple filenames.
See: Filename, File Reference, Master File Table (MFT), and NTFS (New Technology Filesystem). |
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| File Reference |
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A 64-bit value that identifies a file on an NTFS volume. The file reference consists of a file number and a sequence number. The file number corresponds to the position of the file’s file record in the Master File Table (MFT) minus one (1) (or to the position of the base of the record minus one (1)) if there is more than one file record. The file reference sequence number, which is incremented each time the MFT file record position is reused, enables NTFS to perform internal consistency checks.
See: Base File Record, File Record, Master File Table (MFT), NTFS (New Technology Filesystem), and Volume. |
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| Filesystem |
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In an operating system, the overall structure in which files are named stored and organised but it is the filesystem drivers (FSDs), of which there are two – local manages volumes directly connected to the computer and Network which allows users to access data volumes connected to remote computes, that manages the filesystem. Although FSDs run in kernel mode they differ in a number of ways from standard kernel-mode drivers. Perhaps most significant, they must register as an FSD with the I/O Manger and they must interact more extensively with the Memory Manager (of which FSDs are heavily reliant upon). For more enhance performance, the FSDs also usually rely on the services of the Cache Manager (of which FSDs are heavily reliant upon). Therefore FSDs use a superset of the exported Ntoskrnl functions that standard drivers use, and can be invoked through several paths.
- Local FSDs include Ntfs.sys, Fastfat.sys, Udfs.sys, Cdfs.sys, and the RAW FSD (integrated in Ntoskrnl.exe). A local FSD is responsible for registering with the I/O Manager. Once the FSD is registered, the I/O Manager can call on it to perform volume recognition when applications or the system initially accesses the volumes. Volume recognition involves an examination of a volume’s boot sector, and often a consistency check, and of the filesystem’s metadata. The first sector of every Windows –supported filesystem format is reserved as the volume’s boot sector. A boot sector contains enough information so that the FSD can both identify the volume on which the sector resides as containing the format that the FSD manages and locate any other metadata necessary to identify where metadata is stored on the volume.
When a local FSD recognises a volume, it creates a device object that represents the mounted filesystem format. The I/O Manager makes a connection through the volume parameter block (VPB – serves as a link between a volume device object and the device object that a FSD creates to represent a mounted filesystem instance for the volume) between the volume’s device object (which is created by a storage device) and the device object that the FSD created. The VPB’s connection results in the I/O Manager redirecting I/O requests targeted at the volume device object to the FSD device object. To improve performance, the local FSDs usually use the Cache Manager to cache the filesystem data including metadata. FSD also integrates with the Memory Manager so that mapped files are implemented correctly.
Local FSD also support filesystem dismount operations, which permit the system to disconnect the FSD from the volume object. A dismount occurs whenever an application requires raw access to the on-disk contents of the volume or the media associated with the volume is changed. The first time an application accesses the media after the dismount, the I/O Manager reinitiates a volume mount operation for the media.
- Remote FSDs consists of two components: a client and a server. A client-side remote FSD (named LANMan Redirector that includes the Workstation service) allows applications to access remote files and directories. The client FSD accepts I/O requests from applications and translates them into network filesystem protocol commands that the FSD sends across the network to a server-side component, which is typical of remote FSD. A server-side FSD (named LANMan Server that includes the Server service) listens for commands coming from the network connection and fulfils them by issuing I/O requests to the local FSD that manages the volume on which the file or directory that the command is intended for resides. Like local FSDs, client-side remote FSDs unusually use the Cache Manager’s services to locally cache file data belonging to remote files and directories. Nevertheless, client-side remote FSDs must implement a distributed cache coherency protocol, of which there are three subtypes, so that the data and application views when it accesses a remote file is the same as the data applications running on other computers that are accessing the same file viewed. Although server-side remote FSDs participate in maintaining cache coherency across their clients, they do not cache data from local FSDs due to the fact that local FSDs cache their own data.
NTFS, FAT32, and FAT (12 and 16) are all types of filesystem formats supported by Microsoft Windows which in turn define the way file data is stored on storage media, and they affect a filesystem’s features, e.g., a format that does not permit user permissions to be associated with files and directories cannot support security, imposes file size limits and so forth. The commonest filesystems in use today are based on a file allocation table, which keeps track of the data stored in each cluster on a hard disk drive. Several varieties of the FAT filesystem exists, e.g., FAT12, FAT16, and FAT32 – all of which are differentiated by the number of digits used in the allocation table numbers. FAT16 uses 16-bit numbers to keep track of data clusters while FAT32 uses 32-bit numbers.
To manage files on a disk and enable all applications to see a consistent interface to the filesystem regardless of the storage hardware type being used, the operating system creates several structures on that disk. These structures are the same for any operating system that supports the FAT filesystem, including Window 9x/Millennium/NT/2000/XP/Server 2003. The following list shows all the structures and areas FAT uses to manage a disk, in roughly the same order in which they appear on the media.
- Master Boot Record (MBR) and Extended Partition Boot Records (EPBR) (sectors).
- Volume Boot Record (VBR).
- Root directory.
- File allocation table.
- Clusters (allocation units in the data area).
- Diagnostic read-and-write cylinder.
A hard disk drive has all these disk-management structures, and a floppy diskette has all but the MBR, EPBR and diagnostic cylinder. The VBR through data area structures are repeated for each partition or volume on a drive. These structures are created on the hard disk drive or other high-capacity media on formatting. If one of these important structures is damaged, serious consequences can ensue. Damage to one of these sensitive structures usually causes a domino effect, limiting access to other areas of the disk or causing further problems in using the disk.
See: Allocation Unit (or Cluster), Boot Sector, Cluster (or Allocation Unit), Directory, Extended Partition, Extended Partition Boot Record (EPBR), FAT (12-, 16-, and 32-bit), File Allocation Table, Master Boot Record (MBR), Partition, Sector, Volume, and Volume Boot Records (VBR)
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| Fixed Disk (or Hard Disk Drive)< |
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Also called a hard disk drive, it is a high-capacity magnetic storage disk unit that cannot be moved from its controller hardware or housing. Made of rigid substrate material/medium (aluminium or a glass/ceramic) with a magnetic coating and used for the mass storage and retrieval of data.
See: Disc & Disk, and Data Loss and Data Recovery. |
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| Floppy Diskette |
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Flat, circular, counterclockwise rotating, removable, flexible magnetic material/medium that can store various types of information, both analogue and digital. Disk is often used in reference to magnetic storage media, e.g., floppy diskette but also fixed disks such as a hard disk drive. The term floppy refers to the flexible nature of the magnetic media only.
See: Fixed Disk (or Hard Disk Drive), and Disc & Disk. |
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| Folder |
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In a graphical user interface (GUI, spoken as GU-EE), a simulated file folder that holds documents (text, data, or graphics), applications, and other folders. A folder is similar to a DOS subdirectory.
See: GUI (Graphical User Interface, spoken as GU-EE). |
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| FORMAT.COM |
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The DOS/Windows format program that performs both low- and high-level formatting on floppy diskettes but only high-level formatting on a hard disk drive (fixed disk).
See: Disc & Disk, and Fixed Disk (or Hard Disk Drive). |
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| Formatted Capacity |
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The total number of data bytes that can fit on a formatted hard disk drive. The unformatted capacity is higher because space is lost defining the boundaries between partitions.
See: Bytes, Data, and Partition. |
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| Formatting |
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| Formatting prepares a hard disk drive, or other types of storage media, so that the computer and therefore the system can read and write to it. Checks the hard disk drive for defects and constructs on an organisational system to manage information on the hard disk drive. High-level formatting creates, among other things, the root directory and FATs and so forth. |
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| Fragmentation |
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The scattering of parts of the same disk file over different areas of the disk. Fragmentation occurs as files on a disk are deleted and new ones are added. Fragmentation degrades the overall performance of disk operations, although not severely except in extreme fragmentation cases.
See: Defragmentation. |
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| Free Space |
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Specifically, available space that can be used to create logical dos drives within an extended partition yet generally it is unoccupied but available space within a volume.
See: Extended Partition, and Volume. |
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