t of the MS-DOS operating system, which arose at Microsoft as a result of an order development for IBM and which was subjected to slight changes, above all to a large number of bug fixes, by IBM before delivery. Version 1.0 came onto the market in 1981, before the first MS-DOS version distributed by Microsoft itself, under the official name "IBM Personal Computer Disk Operation System 1.0", but was even then simply called "PC DOS" for short. The versions 3.30 to 5.02 ran under the official name "IBM DOS" and from version 6.1 the system was marketed as "IBM PC DOS".
Compared to generic MS-DOS editions, PC DOS had various optimizations. Some of them could only run on original IBM PCs and 100% compatible machines. The technical further development took place alternately at both Microsoft and IBM.
PC DOS was further developed to be compatible with MS-DOS (Windows 3.x) up to version 6.3 from 1993, whereby version 6.1 of MS-DOS 6.0 already differed more clearly than the previous versions and PC DOS was also marketed as an alternative for PCs from other manufacturers has been. The current versions PC DOS 7.0 (Revision 0, 1994) with REXX , PCMCIA , DPMS and XDF support, Stacker Disk Compression and a powerful text editor and help system, PC DOS 2000 (PC DOS 7.0 Revision 1, 1998) with year -2000 -Fixes and Euro support and OEM PC DOS 7.1 (2003) with LBA / FAT32 support are independent further developments by IBM, in which Microsoft no longer played a part.
DR-DOS (up to and including version 6.0 still DR DOS ) was originally developed by Digital Research as an answer to MS-DOS, since MS-DOS, originally a clone of CP / M-80 for 8086 processors, was contracted with IBM advanced to become the standard operating system for the IBM PC and the large market of compatible computers. Such a supremacy among the operating systems for microcomputers was previously held by Digital Research's CP / M operating system family, which has now been increasingly replaced by MS-DOS. DR-DOS can be seen as a further development of CP / M (here especially CP / M-86) in the direction of MS-DOS / PC DOS. In fact, through this relationship, the genesis of some (only a few) routines at the source code level can be traced back to 1976, i.e. long before the introduction of the IBM PC, even if the development of DR-DOS as such did not begin until much later has been.
The development of MS-DOS / PC DOS-compatible operating systems began at Digital Research in 1983 with the development of the DOS emulator PCMODE, an additional module for their own operating system Concurrent CP / M-86 3.1 (BDOS- Kernel 3.1). The DR Concurrent CP / M-86 was a multitasking version of the CP / M-86. With the next version of the operating system in 1984, the emulator became an integral part of the system, which was accordingly renamed DR Concurrent DOS 3.2 (with BDOS kernel 3.2). The CDOS OEM adaptation for IBM PC compatible computers was expressed by the additional designation "PC" in the name of DR Concurrent PC DOS (alias CPCDOS). This Digital Research operating system could run CP / M-86 and MS-DOS / PC-DOS-1.1 applications at the same time. Despite the similarity of names, the system must be strictly distinguished from IBM PC DOS, which as an MS-DOS OEM version offered neither CP / M-86 compatibility nor multitasking. Later versions of CDOS also supported EEMS bank switching (CDOS 86 / XM, 1986) and used the 286 or 386 protected mode (CDOS 286, 1985, or CDOS 386, 1987) for memory management and multitasking. The DOS emulator was also increasingly developed and offered compatibility with DOS 2.x / 3.x / 5.x applications. Further developments of Concurrent DOS were FlexOS and Multiuser DOS (MDOS), from which Datapac System Manager and IMS REAL / 32 developed much later. CDOS, FlexOS and MDOS were mainly used in professional environments and for industrial control tasks because of their high reliability and were not widely used on normal desktop computers.
Digital Research made several attempts to gain a foothold in the desktop market with its own MS-DOS / PC-DOS-compatible operati