Disk formatting |
Disk formatting is the process of preparing a hard disk or other storage medium for use with the file system (File Allocation Table, NTFS, Unix File System, etc.) of an operating system. A variety of utilities and programs exist for this task; pictured to the right is the iconic FORMAT.COM of MS-DOS and PC-DOS.
Large disks can be hard disk drive partitioning, divided into partition (computing)s that are formatted with their own file systems. This is normally only done on hard disks because of the unfeasibly small sizes and compatibility issues of other disk types.
Formatting a drive (or partition) destroys the computer s records of the data it contains, effectively deleting it. It s vital to make back-ups of important data beforehand, although see below. A format can be used to revert a corrupted operating system to a fresh state by reformatting the disk and reinstalling the OS, and as a drastic way of combatting a Software problem or a computer virus.
As with regular deletion, data from a format is not destroyed until overwritten and may be recoverable unless securely deleted ( shred ). Low-level formatting, below, is frequently confused with zero-writing in which every bit of data on the disk is systematically overwritten with zeros returning £the drive to a factory-fresh state.
A formatting of a disk involves two quite different processes known as low-level formatting and high-level formatting. The former deals with formatting of disk surfaces required by the disk controller hardware; the latter with software-specific information written by a specific operating system.
Formatting programs ask for confirmation beforehand to prevent accidental removal of data. In several versions of MS-DOS, there is an undocumented parameter called /autotest which allows the FORMAT program to skip the confirmation message.
There is also the undocumented /u parameter (format drive letter /u) that performs an unconditional format, overwriting the partition with Hex F6 (zeros) [http://www.mdgx.com/secrets.htm#FORMAT-U 1]. No unformatting utility can recover data from a partition that was formatted by the /u parameter. This is not the most secure way of destroying the previous data, instead use something like DBAN to destroy old data.
=Formatting a floppy disk=
==Low-level formatting==
Warning: The below information on low-level formatting of floppy disks may be technically incorrect.
The process is most easily seen with a standard 1.44MB PC floppy disk. Low-level formatting of the floppy normally writes 18 sectors of 512 bytes each on each of 160 tracks (80 on each side) of a floppy disk. That provides 1,474,560 bytes of storage on the floppy. This means that the actual storage capacity of the disk is 1.40625MB. (Sectors are actually larger than 512 bytes as they include sector numbers, CRC bytes, and other information required in order to identify and verify the sector during reading and writing. These additional bytes do not add to the overall storage capacity of the disk) Low-level formatting installs characteristics like sector numbers that are visible to, and used by, the hardware and disk controller. To further complicate the concept, different low-level formats can be used on the same medium; for example, large records can be used to cut down on interrecord gap size. Linux supports a variety of sector sizes, and DOS and Microsoft Windows support a large-record-size DMF-formatted floppy format.
==High-level formatting==
On the other hand, high-level formatting is unique to a file system. In the case of MS-DOS (File Allocation Table), the write of an initial boot record—which may just contain code to indicate the disk is not bootable—is required, as well as two copies of the file allocation table and an empty root directory.
In the case of floppy disks, both high- and low-level formatting are customarily done in one pass by user software—FORMAT.COM in the case of DOS. In recent years, most floppies have shipped preformatted from the factory as DOS FAT12 floppies. It is possible—if not always easy—to format them again to other formats.
=Formatting a hard disk drive=
==Low-level formatting==
Low-level formatting of hard disks was common in the 1980s. Typically this involved setting up the Modified Frequency Modulation pattern on the disk, so that sectors of bytes could be successfully written to it. With the advent of Run Length Limited encoding, low-level formatting grew increasingly uncommon, and most modern hard disks are embedded systems, which are low-level formatted at the factory and thus not subject to user intervention.
Early hard disks were quite similar to floppies, but the low-level formatting was generally done by the BIOS, rather than by the operating system. This was a fairly bizarre process that involved using the MS-DOS debug computer program to transfer control to a routine hidden at different addresses in different BIOSs.
Starting in the early 1990s, the low-level formatting of hard drives became more complex as technology improved to
*use Run Length Limited encoding *use different numbers of sectors per track on longer outer tracks. *encode track numbers into the disk surface to simplify hardware and increase the speed of head motion, etc.
Rather than face ever-escalating difficulties with BIOS versioning, disk vendors started doing low-level formatting at the factory. High level formatting is done on a per-partition basis, and it formats the partition to work with a specific file format.
Today, an end-user, in most cases, should never perform a low-level formatting of an IDE or ATA hard drive; disk reinitialization an IDE or ATA hard drive is much more common. [http://freepctech.com/pc/001/007.shtml The NOSPIN Group]
=References=
*The NOSPIN Group, Inc. (n.d.). Low level formatting an IDE hard drive . Retrieved December 24, 2003 from [http://freepctech.com/pc/001/007.shtml]
=External links=
*[http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html Secure Deletion of Data from Magnetic and Solid-State Memory ] by Peter Gutmann *[http://www.jegsworks.com/Lessons/lesson6/lesson6-3.htm Illustrated guide ] on Jegsworks|
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