Editing Disk formatting (section)

== History ==

A [[Block (data storage)|block]], a contiguous number of [[byte]]s, 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 [[IBM 1301|1301]]<ref>{{cite web |url=http://www-03.ibm.com/ibm/history/exhibits/storage/storage_1301.html |archive-url=https://web.archive.org/web/20050426065056/http://www-03.ibm.com/ibm/history/exhibits/storage/storage_1301.html |url-status=dead |archive-date=April 26, 2005 |title=IBM&nbsp;1301 disk storage unit |date=23 January 2003 |publisher=[[IBM]] |access-date=2010-06-24}}</ref> 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 device]]s on the [[IBM System/360]] expanded this concept in the form of [[Count Key Data]] (CKD) and later [[Count Key Data#ECKD|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.<ref>{{cite web |url=http://www-03.ibm.com/ibm/history/exhibits/storage/storage_3390.html |archive-url=https://web.archive.org/web/20050124005029/http://www-03.ibm.com/ibm/history/exhibits/storage/storage_3390.html |url-status=dead |archive-date=January 24, 2005 |title=IBM 3390 direct access storage device |date=23 January 2003 |publisher=[[IBM]]}}</ref>

Modern hard disk drives, such as [[Serial attached SCSI]] (SAS)<ref group="lower-alpha">"The LBAs on a logical unit shall begin with zero and shall be contiguous up to the last logical block on the logical unit"., Information technology&nbsp;— Serial Attached SCSI - 2 (SAS-2), INCITS 457 Draft 2, May 8, 2009, chapter 4.1 Direct-access block device type model overview.</ref> and [[Serial ATA]] (SATA)<ref>ISO/IEC 791D:1994, AT Attachment Interface for Disk Drives (ATA-1), section 7.1.2</ref> drives, appear at their [[interface (computing)|interface]]s 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.<ref>{{cite web |url=http://www.anandtech.com/show/2888 |title=Western Digital's Advanced Format: The 4K Sector Transition Begins |author-first=Ryan |author-last=Smith |date=2009-12-18 |publisher=[[Anandtech]]}}</ref><ref>{{cite web |url=http://www.seagate.com/tech-insights/advanced-format-4k-sector-hard-drives-master-ti/ |title=Transition to Advanced Format 4K Sector Hard Drives |publisher=[[Seagate Technology]]}}</ref>

[[Floppy disk]]s generally only used fixed block sizes but these sizes were a function of the host's [[Operating System|OS]] and its interaction with its [[Floppy disk controller|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 disc]]s generally only use fixed block sizes.