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Concept
Disk formatting
Summary
Disk formatting is the process of preparing a data storage device such as a hard disk drive, solid-state drive, floppy disk, memory card or USB flash drive for initial use. In some cases, the formatting operation may also create one or more new s. 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, dividing the device into several sub-devices and, in some cases, writing information to the device allowing an operating system to be booted from it. 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 . Some formatting utilities allow distinguishing between a quick format, which does not erase all existing data and a long option that does erase all existing data.
As a general rule, formatting a disk by default leaves most if not all existing data on the disk medium; some or most of which might be recoverable with privileged or 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 six-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 and other direct access storage devices 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.
Official source
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