Editing IBM PC DOS (section)

=== {{anchor|3.00|3.10|3.20|3.21|3.30}}PC DOS 3.x ===
[[File:IBM DOS 3.30 Retail Box.jpg|thumb|Retail box of IBM PC DOS 3.30]]
In August 1984, IBM introduced the [[Intel 80286]]-derived [[IBM PC/AT]], its next-generation machine. Along with this was DOS 3.00. Despite jumping a whole version number, it again proved little more than an incremental upgrade, adding nothing more substantial than support for the AT's new 1.2 [[megabyte]] (MB) floppy disks. Planned networking capabilities in DOS 3.00 were judged too buggy to be usable and Microsoft disabled them prior to the OS's release. In any case, IBM's original plans for the AT had been to equip it with a proper next-generation OS that would use its extended features, but this never materialized.<ref name="Wallace_1992"/> PC&nbsp;DOS 3.1 (released March 1985) fixed the bugs in DOS 3.00 and supported IBM's Network Adapter card on the [[IBM PC Network]]. PC&nbsp;DOS 3.2 added support for {{frac|3|1|2}}-inch double-density 720&nbsp;KB floppy disk drives, supporting the [[IBM PC Convertible]], IBM's first computer to use {{frac|3|1|2}}-inch floppy disks, released April 1986, and later the [[IBM Personal System/2]] in 1987.

In June 1985, IBM and Microsoft signed a long-term Joint Development Agreement to share specified DOS code and create a new operating system from scratch, known at the time as Advanced DOS. On 2 April 1987 [[OS/2]] was announced as the first product produced under the agreement.<ref name="Necasek_2004"/> At the same time, IBM released its next generation of personal computers, the [[IBM Personal System/2]] (PS/2).<ref name="Wallace_1992"/> PC&nbsp;DOS 3.3, released with the PS/2 line, added support for high density {{frac|3|1|2}}-inch 1.44&nbsp;MB floppy disk drives, which IBM introduced in its 80286-based and higher PS/2 models. The upgrade from DOS 3.2 to 3.3 was completely written by IBM, with no development effort on the part of Microsoft, who were working on "Advanced DOS 1.0". DOS 3.30 was the last version designed with the IBM XT and floppy-only systems in mind; it became one of the most popular versions and many users preferred it to its buggy successor.