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Disk formatting is the only process of preparing the layout of data how to store in a hard disk or other storage medium and we call this layout: the file system (FAT, NTFS, UFS, etc.). 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 partitioned, divided into logical sections 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, but High-level format will not destroy the data itself, just only erase the header record of the data which may be recovered later in some cases. 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 ("shredded"). Low-level formatting, below, is frequently confused with "zero-writing" of "fill-zero" 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 which overwrites the partition with Hex F6 (zeros) *. 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, however no disk wiping software guarantees 100% destruction of stored data. Only physically destroying the hard drive itself along with the magnetic particles will guarantee complete security.
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. The 1.44MB naming is somewhat misleading, as it's made by calculating the capacity with both powers of two and powers of ten (1.44 * 1024 * 1000 = 1,474,560). 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. (Sectors are actually physically 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 media; for example, large records can be used to cut down on interrecord gap size. Linux supports a variety of sector sizes, and DOS and 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 (FAT 16), the writing 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.
Technical Review
PC CLINIC Technician:
Low-level formatting erases all data including MBR (Master Boot Record - The 1st sector of a disk, it's a record of partitions and where the boot loader is located.), data header (Keeps track of what data is recorded in that sector, because in many cases, a file will split its information up throughout one or more sectors.) and data area (The place where your data is really saved). So, with low-level formatting, data cannot be recovered. The process of low-level formatting a hard disk is extremely time consuming. It's only good for hard disk capacity below 2GB. (low-level formatting a 4GB hard disk may take more than 13 hours). High-level formatting only rewrites the MBR with the new partition info and rewrites data header as empty space but the data still remains until new data overwrites the old data. (The reason why the data can be recovered, but folders' names may be lost and data-recovery programs will generate new folder names using random numbers and letters for those folders recovered.) Thehe process of high-level formatting is still time consuming in formatting a large capacity hard disk (e.g. 40GB may take 2 hours or more to finish depending on the hard disk specification).
Quick Formatting
Quick Formatting only rewrites the MBR and the first few sectors of the disk and marks them as available; however, the data is left intact (so we can recover all data and folder names). Currently, almost all technicians use quick format when formatting a new hard disk, using low-level and high-level format only when the disk is having problems.
Many Partitioning Tools using quick format like Windows XP bootdisk, Partition Magic, EZdrive, etc.
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Formatting in DOS
Later versions of the DOS FORMAT command had several options that were often misunderstood.- FORMAT /Q: the "quick format", which merely blanked the directory and FAT
- FORMAT /U: the "unconditional format", which actually rewrote the low level formatting of the disk
Some versions of DOS had an uncodumented FORMAT /AUTOTEST option; if done, the usual warning line is not given and DOS begins to format right away. The WM/FormatC macro virus uses this command to format C: as soon as a document is opened.
Formatting using other programs
Several freeware and shareware programs existed which allowed considerably more control over formatting, including the option to create formats similar to DMF, examples being a program called FDFORMAT, NFORMAT and 2M. A user could format high-density 3 1/2" disks with capacity up to 2 MB. Options included:- Change cluster size: While Microsoft defaulted to 2 sectors per cluster on low density media and 1 on high density, this could be altered by most alternative formatters, with no significant compatibility issues.
- Head/track sector skew: By moving the sector numbering forward at side change and track stepping to allow for mechanical delay, sequential transfer could be optimized.
- Interleave sectors: Not usually required, unless using a minimum sector gap when increasing the number of sectors per track.
- Sectors per track: While a normal 1.44MB format uses 18 sectors per track, it was possible to increase this to a maximum of 21
- Extra tracks: Most drives could tolerate extension to 82 tracks, though while some could handle more, there was a risk of jamming others.
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 MFM pattern on the disk, so that sectors of bytes could be successfully written to it. With the advent of RLL 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 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 RLL 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. The NOSPIN Group
References
- The NOSPIN Group, Inc. (n.d.). Low level formatting an IDE hard drive. Retrieved December 24, 2003 from *
See also
External links
- Secure Deletion of Data from Magnetic and Solid-State Memory by Peter Gutmann
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"Disk formatting"