Editing Disk formatting (section)

=== Low-level formatting (LLF) of hard disks ===
[[File:IBM PC XT 10 meg MFM low level format.jpg|thumb|Low-level format of a 10-megabyte [[IBM Personal Computer XT|IBM PC XT]] hard drive]]

Hard disk drives prior to the 1990s typically had a separate [[disk controller]] that defined how data was encoded on the media. With the media, the drive and/or the controller possibly procured from separate vendors, users were often able to perform low-level formatting. Separate procurement also had the potential of incompatibility between the separate components such that the subsystem would not reliably store data.<ref group="lower-alpha">This problem became common in PCs where users used RLL controllers with MFM drives; [https://web.archive.org/web/20180609221448/http://webpages.charter.net/dperr/diskguid.txt "MFM drives should not be used on RLL controllers.".]</ref>

User-instigated low-level formatting (LLF) of [[hard disk drives]] was common for [[minicomputer]] and [[personal computer]] systems until the 1990s. [[IBM]] and other mainframe system vendors typically supplied their hard disk drives (or media in the case of removable media HDDs) with a low-level format. Typically this involved subdividing each track on the disk into one or more blocks which would contain the user data and associated control information. Different computers used different block sizes and IBM notably used [[Count Key Data|variable block sizes]] but the popularity of the IBM PC caused the industry to adopt a standard of 512 user data bytes per block by the middle 1980s.

Depending upon the system, low-level formatting was generally done by an operating system utility. IBM compatible PCs used the BIOS, which is invoked using the MS-DOS [[DEBUG (DOS Command)|debug]] program, to transfer control to a routine hidden at different addresses in different BIOSes.<ref>[http://support.microsoft.com/kb/60089 Using DEBUG to Start a Low-Level Format], Microsoft</ref>

==== Transition away from LLF ====

Starting in the late 1980s, driven by the volume of IBM compatible PCs, HDDs became routinely available pre-formatted with a compatible low-level format. At the same time, the industry moved from [[Hard disk drive interface#BSDI|''historical (dumb) bit serial interfaces'']] to modern (intelligent) [[Hard disk drive interface#BSI|''bit serial interfaces'']] and [[Hard disk drive interface#WSI|''word serial interfaces'']] wherein the low-level format was performed at the factory.<ref>{{cite web|publisher=The NOSPIN Group, Inc.|url=http://freepctech.com/pc/001/007.shtml|title=Low level formatting an IDE hard drive|website=FreePCTech.com|archive-url=https://web.archive.org/web/20120716043736/http://freepctech.com/pc/001/007.shtml|archive-date=July 16, 2012|access-date=December 24, 2003}}</ref><ref>{{cite web|website=The PC Guide. Site Version: 2.2.0 - Version Date: April 17, 2001|url=http://www.pcguide.com/ref/hdd/geom/formatUtilities-c.html|title=Low-Level Format, Zero-Fill and Diagnostic Utilities|access-date=May 24, 2007|archive-url=https://web.archive.org/web/20190103014814/http://www.pcguide.com/ref/hdd/geom/formatUtilities-c.html|archive-date= January 3, 2019}}</ref>  Accordingly, it is not possible for an end user to low-level format a modern hard disk drive.