Disk formatting

Disk formatting is the process of preparing a data storage device such as a hard disk drive, solid-state drive, floppy disk or USB flash drive for initial use. In some cases, the formatting operation may also create one or more new file systems. The first part of the formatting process that performs basic medium preparation is often referred to as 'low-level formatting'. Partitioning is the common term for the second part of the process, making the data storage device visible to an operating system. The third part of the process, usually termed 'high-level formatting' most often refers to the process of generating a new file system. In some operating systems all or parts of these three processes can be combined or repeated at different levels and the term 'format' is understood to mean an operation in which a new disk medium is fully prepared to store files. Disk formatting is the process of preparing a data storage device such as a hard disk drive, solid-state drive, floppy disk or USB flash drive for initial use. In some cases, the formatting operation may also create one or more new file systems. The first part of the formatting process that performs basic medium preparation is often referred to as 'low-level formatting'. Partitioning is the common term for the second part of the process, making the data storage device visible to an operating system. The third part of the process, usually termed 'high-level formatting' most often refers to the process of generating a new file system. In some operating systems all or parts of these three processes can be combined or repeated at different levels and the term 'format' is understood to mean an operation in which a new disk medium is fully prepared to store files. As a general rule, formatting a disk leaves most if not all existing data on the disk medium; some or most of which might be recoverable with special tools. Special tools can remove user data by a single overwrite of all files and free space. A block, a contiguous number of bytes, is the minimum unit of storage that is read from and written to a disk by a disk driver. The earliest disk drives had fixed block sizes (e.g. the IBM 350 disk storage unit (of the late 1950s) block size was 100 6 bit characters) but starting with the 1301 IBM marketed subsystems that featured variable block sizes: a particular track could have blocks of different sizes. The disk subsystems on the IBM System/360 expanded this concept in the form of Count Key Data (CKD) and later Extended Count Key Data (ECKD); however the use of variable block size in HDDs fell out of use in the 1990s; one of the last HDDs to support variable block size was the IBM 3390 Model 9, announced May 1993. Modern hard disk drives, such as Serial attached SCSI (SAS) and Serial ATA (SATA) drives, appear at their interfaces as a contiguous set of fixed-size blocks; for many years 512 bytes long but beginning in 2009 and accelerating through 2011, all major hard disk drive manufacturers began releasing hard disk drive platforms using the Advanced Format of 4096 byte logical blocks. Floppy disks generally only used fixed block sizes but these sizes were a function of the host's OS and its interaction with its controller so that a particular type of media (e.g., 5¼-inch DSDD) would have different block sizes depending upon the host OS and controller. Optical discs generally only use fixed block sizes. Formatting a disk for use by an operating system and its applications typically involves three different processes.