IBM and several other PC manufacturers all sold customized versions of Microsoft's MS-DOS, and that there was a competitor called DR-DOS.

Gary Kildall, whom we left several pages ago spurning IBM's offer to create the operating system for the PC, went on to finish his 16-bit operating system, called CP/M-86. Kildall sued IBM and Microsoft for copying CP/M, and eventually reached a settlement whereby IBM agreed to offer CP/M-86 in addition to PC-DOS. And IBM did offer CP/M-86, for $240 a copy, versus $40 for PC-DOS. It didn't sell well.

By 1987, Kildall had abandoned the idea of promoting CP/M in the 16-bit world. Killdall's company Digital Research eventually produced an MS-DOS clone called DR-DOS, which never, as they say, made the big bucks, but did force Microsoft to significantly lower its prices and make enhancements to MS-DOS that otherwise might never have been made. Anyone who's used edit to edit a text file has Digital Research to thank. Digital Research also produced GEM, a graphical operating system that predated and competed with Windowsmore on that shortly. DR-DOS ultimately did not survive, although various legal battles continued. In 2000, Microsoft paid Digital Research's successor company a reputed $150$200 million to settle suits over the licensing and marketing practices that drove DR-DOS under.

Besides DR-DOS, other operating systems came and went, or came and stayed, including these more popular ones:

• OS/2 IBM and Microsoft initially collaborated to create OS/2, a 32-bit protected-mode advanced operating system that was intended to eventually replace DOS. Later versions sported a user interface that served as the inspiration for Windows 95. It was incredibly reliable and seemed to be the future of PC operating systems, but in 1991 Microsoft and IBM parted ways. Microsoft went on to develop Windows NT, which begat Windows 2000 and XP (more on that in the next section). IBM doggedly tried keep OS/2 alive and didn't give up until mid-2005. It eventually found a niche as a network server operating system and as a host for industrial control systems. You may never have seen a computer running it, but you've probably been in buildings whose air conditioning systems were controlled by it. It's sad reallyhad the Microsoft/IBM partnership survived, we'd all be using OS/2 today, and we would probably have had Windows XP's reliability 10 years earlier.

• Novell NetWare Novell Corporation's NetWare operating system is a platform for file and print servers used in corporate environments. It reigned supreme in this market for many years, was exceedingly reliable and fast, and it commanded a premium price until it was displaced by Microsoft Windows NT, which significantly undercut it in price, while never matching NetWare's reliability or performance. It's still widely used in large corporate environments, primarily for its excellent directory system, and is the competitive target at which Microsoft's Active Directory is aimed. Novell is now moving its corporate network service software away from the proprietary operating system and into Linux.

• Banyan Vines Vines was another high-end network server operating system. It had user directory features that were advanced for its time, but it eventually lost its market share to Novell and withered on the (sorry for this) vine.

• UNIX Many versions of the UNIX operating system were developed for the PC architecture. UNIX was originally created as a "programmer's workbench" by computer scientists at AT&T's Bell Laboratories, and was given away free to universities during the 1970s and 1980s. The result was a generation of programmers (including your author) who were trained in this elegant but somewhat cryptic environment. PC flavors of UNIX include AT&T licensees Xenix and SCO UNIX, and clones XINU, NetBSD, FreeBSD, Linux, and several others.

• Pick - Pick was a database system that in some cases was packaged as a standalone operating system. It was one of the earliest multiuser systems for the PC architecture.

Other operating systems were developed, including a multiuser dBASE-like system that I remember seeing once, but they've faded to total obscurity.