CP/K

Digital Research
Industry	Software
Founded	1974
Founder	Gary Kildall
Headquarters	United States
Products	CP/M, CP/M-86, MP/M-86, Concurrent DOS, Multiuser DOS, FlexOS, DOS Plus, DR DOS

CP/M-86 represents a now-obsolete iteration of the CP/M operating system, engineered by Digital Research (DR) specifically for the Intel 8086 and Intel 8088 CPU architectures. It preserved command-line compatibility with CP/M-80 and employed the relocatable .CMD file format for executable programs. Digital Research also developed a multi-user, multitasking operating system compatible with CP/M-86 named MP/M-86, which later evolved into Concurrent CP/M-86. Incorporating PC DOS emulation capabilities, this system was rebranded as Concurrent DOS, eventually becoming Multiuser DOS, whose latest release is known as REAL/32. The operating systems FlexOS, DOS Plus, and DR DOS trace their origins back to Concurrent DOS.

History

Originally slated for release in November 1979, Digital Research's CP/M-86 encountered several postponements. When IBM required an operating system for its IBM PC, CP/M-86 was initially favored due to the extensive software ecosystem surrounding CP/M. However, negotiations broke down over IBM’s insistence on a non-disclosure agreement and preference for a single payment rather than Digital Research’s royalty-based licensing model. Subsequently, after discussions with Microsoft, IBM opted for 86-DOS (also known as QDOS), an OS resembling CP/M that Microsoft had acquired from Seattle Computer Products. Microsoft adapted and rebranded it as MS-DOS for the IBM PC and licensed it to IBM as PC DOS. Following threats of legal action from Digital Research founder Gary Kildall over intellectual property concerns, IBM offered CP/M-86 as an alternative operating system option for the PC. The majority of CP/M-86 BIOS drivers for the IBM PC were created by Andy Johnson-Laird.

Upon its launch on 12 August 1981, the IBM PC was shipped starting in October with three available operating systems: PC DOS, CP/M-86, and UCSD p-System. Digital Research released CP/M-86 approximately six months after PC DOS in spring 1982; transitioning applications from CP/M-80 to either platform presented similar challenges. Additionally, in November 1981, a version tailored for the proprietary IBM Displaywriter was introduced.

Certain dual-processor systems combining 8-bit and 16-bit CPUs supported specialized versions of CP/M-86 capable of running both CP/M-86 and CP/M-80 software natively. For instance, the DEC Rainbow utilized CP/M-86/80, while the CompuPro System 816 ran CP/M 8-16. Similarly, the Zenith Z-100 could execute programs designed for both processor types.

As IBM PC clones became widespread, Microsoft broadly licensed MS-DOS. Technical evaluations revealed that although CP/M-86 provided more advanced memory management features, DOS generally delivered faster performance. BYTE magazine observed that Microsoft reserved multitasking functionality for Xenix, thereby leaving an opportunity for Concurrent CP/M-86 in that domain.

Despite its technical merits, CP/M-86 was priced at $240 per license compared to $40 for PC DOS, resulting in substantially lower sales figures; market surveys indicated that 96.3% of IBM PCs were shipped with DOS, while only 3.4% carried CP/M-86 or Concurrent CP/M-86. By mid-1982, leading software publishers such as Lifeboat Associates shifted their support toward DOS. BYTE cautioned that backing from IBM, Microsoft, and Lifeboat posed a significant threat to the viability of CP/M-86. Industry analysts criticized Digital Research's marketing strategy as ineffective.

By early 1983, Digital Research offered version 1.1 of CP/M-86 directly to consumers at $60 per copy, emphasizing instant access to a large professional software library and bundling Graphics System Extension (GSX). The company further expanded retail distribution channels. In May 1983, Digital Research announced intentions to develop DOS-compatible versions of its programming languages and utilities—acknowledging DOS’s market dominance but denying this influenced their approach. Early in 1984, promotional campaigns included complimentary copies of Concurrent CP/M-86 bundled with application software; these applications were distributed on self-booting disks that did not require manually loading CP/M-86 first.

In January 1984, Digital Research launched Kanji CP/M-86—a Japanese-language variant—collaborating with nine Japanese corporations including Mitsubishi Electric and Sanyo Electric. Later that year, Fujitsu introduced FM-16-based systems running Kanji CP/M-86.

Although sharing similar capabilities, CP/M-86 and DOS were incompatible due to differences in system calls and executable file formats; consequently, software needed to be developed separately for each environment. Their command-line interfaces offered analogous functions but differed syntactically—for example, copying files used PIP TARGET=SOURCE on CP/M versus COPY SOURCE TARGET on DOS.

Initially, MS-DOS and CP/M-86 operated on hardware platforms lacking full compatibility with the IBM PC architecture (such as Apricot and Sirius machines), aiming to achieve software portability through standardized system calls customized per hardware configuration. Nevertheless, performance-critical applications frequently accessed IBM PC hardware directly—favoring versions optimized specifically for the PC—which outperformed others notably in gaming titles writing directly to video memory rather than relying on OS-mediated calls. This trend led to widespread adoption of hardware architectures identical to the IBM PC design, which imposed a memory ceiling of 640 KB; earlier MS-DOS and CP/M-86 systems without this limitation could utilize nearly one megabyte of RAM.

Reception

PC Magazine observed that CP/M-86 appeared to be "better suited for the PC" than DOS in multiple respects; however, its significantly higher cost—approximately six times that of DOS—diminished its attractiveness for users who were not engaged in assembly language programming. The review underscored CP/M-86's advantages in areas where DOS showed weaknesses, and vice versa, stressing that the extent of application compatibility would ultimately influence its commercial success. A notable limitation was the absence of a run-time version for CP/M-86 applications.

Versions

CP/M-86 releases are identified by two version numbers: one representing the entire operating system (displayed during startup) and another for the underlying BDOS kernel. The following versions are documented:

Operating System	BDOS Version	Release Date	Remarks
CP/M-86 1.0 for AST	2.2?	circa 1981
CP/M-86 1.0 for Altos ACS 16000/8600	2.2?	November 1981
CP/M-86 Version 1.1 for IBM Displaywriter	2.2	November 1981
CP/M-86 1.0 for Sirius 1/Victor 9000	2.2a	1981/1982
CompuView CP/M-86	2.x?	1982	Compatible with IBM PC hardware; supports 196 KB disk capacity
IBM CP/M-86 for IBM PC Version 1.0	2.2	April 1982	Initial launch; supports 141 KB disk capacity
IBM CP/M-86 for IBM PC Version 1.1	2.2	March 1983	Introduced hard drive compatibility
CP/M-86 Plus Version 3.1	3.1	October 1983	Designed for Apricot PC; multitasking kernel enabling up to four concurrent tasks
Personal CP/M-86 Version 1.0	3.1	November 1983	Released for Siemens PG685
Personal CP/M-86 Version 3.1	3.3	January 1985	For Apricot Computers F-Series; added support for DOS FAT-formatted disks
Personal CP/M-86 Version 2.0	4.1	From 1986 onward	Targeted Siemens PC16-20; shares BDOS with DOS Plus 1.2
Personal CP/M-86 Version 2.11	4.1	From 1986 onward	Designed for Siemens PG685

All variants under Personal CP/M-86 are derived from the CP/M-86 Plus codebase, as indicated by their references.

In addition, several Eastern Bloc adaptations of CP/M-86 existed, bearing names such as SCP1700, CP/K, and K8918-OS, developed by East German companies VEB Robotron in Dresden and Berlin.

Legacy

Since 1997, Caldera has authorized the redistribution and modification of all original Digital Research materials, including source code related to the CP/M family, through Tim Olmstead's "The Unofficial CP/M Web site." Following Olmstead's passing in 2001, this free distribution license was renewed and expanded by Lineo, then the owner of these Digital Research assets, on October 19, 2001.

External links

The Unofficial CP/M Website – authorized distributor of original Digital Research software
The comp.os.cpm FAQ