DR-DOS
DR-DOS is an MS-DOS-compatible operating system for IBM PC-compatible personal computers. It was originally developed by Gary Kildall's Digital Research and derived from Concurrent PC DOS 6.0, which itself was an advanced successor to CP/M-86. Because it changed owners several times, several later versions were produced, such as Novell DOS, Caldera OpenDOS, etc.
History
Origins in CP/M
Digital Research's original CP/M for 8-bit systems based on the Intel 8080 and Z-80 processors spawned several derivative versions, most notably CP/M-86 for the Intel 8086/8088 family of processors. Although CP/M had dominated the market, in 1981 the IBM PC brought about a massive change.
IBM originally approached Digital Research, looking for an x86 version of CP/M. However, due to disagreements over the contract, IBM scrapped the deal and signed with Microsoft, which bought its 86-DOS operating system from Seattle Computer Products to convert it into MS-DOS and IBM PC DOS. The instruction structure and API of 86-DOS mimicked CP/M so Digital Research sued. IBM agreed to sell CP/M-86 at the same time as PC DOS. However, while PC DOS was selling for $40, CP/M-86 was selling for $240.
Digital Research tried to promote CP/M-86 and its multi-user multitasking successor Concurrent CP/M-86 but eventually gave up and modified Concurrent CP/M-86 to run the same applications as MS-DOS and PC DOS.
DOS Plus was initially developed by Digital Research as a stripped down, single-user version of Concurrent DOS but it turned out to perform poorly. Digital Research made a second attempt this time creating a native system. The new operating system was released in 1988 as DR DOS.
The first DR-DOS
Since Digital Research could not compete with the dominance of MS-DOS, it decided to modify its operating system to be compatible with Microsoft's, and thus, in 1988, DR DOS 3.31 was born, compatible with Compaq MS-DOS 3.31. At that time, MS-DOS was only sold pre-installed, and DR-DOS tried to compete on two fronts: on the one hand, it went on sale in stores; on the other, it offered manufacturers cheaper licenses.
The most relevant version
The most important version of DR DOS was version 5.0, in 1990. Released to compete with MS-DOS 4.x, it included a graphical file manager (ViewMAX), and the ability to load the system into high memory on computers with a 286 processor and load devices in UMB blocks, something very useful for users who had to manage more and more hardware but were still limited to 640 KB of conventional memory, which was sometimes limited to 400 KB after installing the drivers. These features were only offered, until then, by applications like QEMM, and not by operating systems.
Competition with Microsoft
The same month that DR-DOS 5.0 appeared, the release of MS-DOS 5.0 was announced, which would ultimately be delayed until the following year. Microsoft's system featured the same memory management capabilities as DR-DOS 5.0, but its command syntax was not fully compatible (for example, DR-DOS used XDEL for what in MS-DOS 5 would be DELTREE and in Windows NT is DEL /S).
Digital Research responded with DR-DOS 6.0 in 1991. Its main features were the SuperStor disk compressor (40MB hard drives were common at the time) and the multitasking capability provided by TaskMax. Although inferior to applications like DesqView, introducing multitasking was a significant improvement over MS-DOS.
In response, Microsoft would include third-party utilities, such as a file compressor (DoubleSpace, later renamed DriveSpace due to legal issues), in its MS-DOS 6.0.
The decline
Digital Research was bought by Novell in its strategy to compete with Microsoft. As a result, Novell DOS 7.0 appeared, whose main advantage over MS-DOS was to offer a personal version of the Novell network system, a system that was beginning to lose popularity due to the appearance of Windows for Workgroups. Eventually, DR-DOS was sold to Caldera in 1996. Caldera's main interest in the product was possibly an old lawsuit against Microsoft for unfair competition, since although the product was highly binary compatible with MS-DOS, Microsoft strove to on introducing code into Windows specifically to make it incompatible with DR-DOS.
Caldera's DR-DOS 7.01 was distributed as freeware for non-commercial use, including source code, under the name OpenDOS, but in version 7.02 it reverted to a completely closed model.
In 2002, the Caldera division dedicated to DR-DOS (Caldera Thinclients, later Lineo), after releasing version 7.03 in 1999, decided to focus on Linux and sold DR-DOS to DeviceLogics, which in 2004 produced DR -DOS 8.0. Lineo's and DeviceLogics' DR-DOS have typically been licensed for use in embedded systems or for utilities that need to use a bootable disk (for example, Seagate's disk utilities).
Meanwhile, the DE-DOS enhancement project has tried to create an operating system from the open source DR-DOS 7.01.