Disk formatting: Encyclopedia II - Disk formatting - Formatting a floppy disk

Disk formatting - Formatting a floppy disk

Disk formatting - 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 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.

Disk formatting - High-level formatting

On the other hand, high-level formatting is unique to a file system. In the case of MS-DOS (FAT12), 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.

Adapted from the Wikipedia article "Formatting a floppy disk", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki