Editing Hard disk drive (section)

=== Formatting ===
{{Main|Disk formatting}}
Data is stored on a hard drive in a series of logical blocks.  Each block is delimited by markers identifying its start and end, error detecting and correcting information, and space between blocks to allow for minor timing variations.  These blocks often contained 512 bytes of usable data, but other sizes have been used.  As drive density increased, an initiative known as [[Advanced Format]] extended the block size to 4096 bytes of usable data, with a resulting significant reduction in the amount of disk space used for block headers, error-checking data, and spacing.

The process of initializing these logical blocks on the physical disk platters is called ''low-level formatting'', which is usually performed at the factory and is not normally changed in the field.<ref>{{cite web|url=http://www.pcguide.com/ref/hdd/geom/formatLow-c.html|title=Low-Level Formatting|access-date=June 28, 2010|archive-url=https://web.archive.org/web/20170604064402/http://www.pcguide.com/ref/hdd/geom/formatLow-c.html|archive-date=June 4, 2017|url-status=dead}}</ref> ''High-level formatting'' writes data structures used by the operating system to organize data files on the disk. This includes writing [[Disk partitioning|partition]] and [[file system]] structures into selected logical blocks. For example, some of the disk space will be used to hold a directory of disk file names and a list of logical blocks associated with a particular file.

Examples of partition mapping scheme include [[master boot record]] (MBR) and [[GUID Partition Table]] (GPT). Examples of data structures stored on disk to retrieve files include the [[File Allocation Table]] (FAT) in the [[DOS]] file system and [[inode]]s in many [[UNIX]] file systems, as well as other operating system data structures (also known as [[metadata]]). As a consequence, not all the space on an HDD is available for user files, but this system overhead is usually small compared with user data.