Editing IBM PC DOS (section)

=== {{anchor|2.00|2.10|2.11}}PC DOS 2.x ===

Later, a group of Microsoft programmers (primarily [[Paul Allen]], [[Mark Zbikowski]] and [[Aaron R. Reynolds|Aaron Reynolds]])<ref name="Duncan_1988"/> began work on PC&nbsp;DOS 2.0. Completely rewritten, DOS 2.0 added subdirectories and hard disk support for the new [[IBM Personal Computer XT|IBM XT]], which debuted in March 1983. A new 9-sector format bumped the capacity of floppy disks to 360&nbsp;KB. The [[Unix]]-inspired kernel featured [[file handle]]s in place of the CP/M-derivative file control blocks and loadable device drivers could now be used for adding hardware beyond that which the IBM PC BIOS supported. BASIC and most of the utilities provided with DOS were substantially upgraded as well. A major undertaking that took almost 10 months of work, DOS 2.0 was more than twice as big as DOS 1.x, occupying around 28&nbsp;KB of RAM compared to the 12&nbsp;KB of its predecessor. It would form the basis for all Microsoft consumer-oriented OSes until 2001, when [[Windows XP]] (based on [[Windows NT]]) was released.<ref name="Duncan_1988"/>

In October 1983 (officially 1 November 1983)<ref name="DOS21"/> DOS 2.1 debuted. It fixed some bugs and added support for half-height floppy drives and the new [[IBM PCjr]].

In 1983, [[Compaq]] released the [[Compaq Portable]], the first 100% [[IBM PC compatible]] and licensed their own OEM version of DOS 1.10 (quickly replaced by DOS 2.00) from Microsoft. Other PC compatibles followed suit, most of which included hardware-specific DOS features, although some were generic.