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 KB of RAM compared to the 12 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. In October 1983 (officially 1 November 1983) 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. 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. PC 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 DOS 3.2 added support for 3½-inch double-density 720 KB floppy disk drives, supporting the IBM PC Convertible, IBM's first computer to use 3½-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. At the same time, IBM released its next generation of personal computers, the IBM Personal System/2 (PS/2). PC DOS 3.3, released with the PS/2 line, added support for high density 3½-inch 1.44 MB floppy disk drives, which IBM introduced in its 80286-based and higher PS/2 models.