CP/M-86

Digital Research
Industry	Computer software
Founded	1970s
Founder	Gary Kildall
Headquarters	United States
Products	CP/M, CP/M-86, MP/M-86, Concurrent CP/M-86, Concurrent DOS, Multiuser DOS, REAL/32, FlexOS, DOS Plus, DR DOS

CP/M-86 was a version of the CP/M operating system developed by Digital Research (DR) specifically for the Intel 8086 and Intel 8088 processors, which has since been discontinued. It preserved compatibility with CP/M-80 command structures and employed the relocatable .CMD file format for its executable programs. Digital Research also produced a multi-user, multitasking operating system compatible with CP/M-86 called MP/M-86, which later evolved into Concurrent CP/M-86. The addition of a PC DOS emulator led to its rebranding as Concurrent DOS, which eventually transformed into Multiuser DOS, with REAL/32 being the most recent iteration. The OS families of FlexOS, DOS Plus, and DR DOS all originated as offshoots of Concurrent DOS.

History

Although originally slated for release in November 1979, Digital Research’s CP/M-86 experienced several postponements. IBM, in search of an operating system for its upcoming IBM PC, initially favored CP/M-86 due to its broad software ecosystem. However, negotiations stalled primarily because IBM insisted on a non-disclosure agreement and preferred a single payment rather than Digital Research’s royalty-based licensing model. Consequently, IBM turned to Microsoft, who licensed 86-DOS (later renamed MS-DOS) from Seattle Computer Products; this was adapted and marketed as PC DOS.

Upon learning of this arrangement, Digital Research’s founder Gary Kildall threatened legal action over intellectual property concerns. In response, IBM offered CP/M-86 as an alternative operating system option on the PC. The majority of CP/M-86 BIOS drivers for the IBM PC were created by Andy Johnson-Laird.

When the IBM PC launched in August 1981, CP/M-86 was available alongside PC DOS and UCSD p-System. However, Digital Research’s release of CP/M-86 for the IBM PC came six months after PC DOS in early 1982; porting applications between CP/M-80 and either OS presented similar challenges. Additionally, in November 1981, Digital Research introduced a CP/M-86 version for the IBM Displaywriter.

Certain dual-processor systems combining 8-bit and 16-bit processors supported specialized versions of CP/M-86 capable of running both CP/M-80 and CP/M-86 applications. Examples include the DEC Rainbow running CP/M-86/80 and CompuPro System 816 operating CP/M 8-16; the Zenith Z-100 was another system supporting software for both processor types.

With the emergence of IBM PC clones, Microsoft widely licensed MS-DOS. Although technically more advanced in memory management capabilities, CP/M-86 operated slower than DOS. BYTE magazine observed that Microsoft’s strategic focus on multitasking through Xenix left room for Concurrent CP/M-86 to compete.

Nevertheless, priced at $240 per license compared to PC DOS’s $40, CP/M-86 struggled commercially; surveys indicated that over 96% of IBM PCs shipped with DOS installed. By mid-1982, key distributors such as Lifeboat Associates had shifted their support predominantly to DOS. Industry commentators and BYTE criticized Digital Research for ineffective marketing strategies.

By early 1983, Digital Research began selling CP/M-86 version 1.1 directly to end users at $60 per copy, emphasizing its extensive software catalog and bundling the Graphics System Extension (GSX). The company also expanded retail distribution and announced plans in May 1983 to release DOS-compatible versions of its programming languages and utilities—acknowledging DOS’s market dominance but denying it influenced their decision-making.

In early 1984, Digital Research promoted Concurrent CP/M-86 by offering free copies bundled with two applications. That January also saw the launch of Kanji CP/M-86 aimed at Japanese corporations such as Mitsubishi Electric and Sanyo; Fujitsu subsequently announced FM-16 systems running this Kanji variant.

While functionally similar, CP/M-86 and DOS were incompatible due to differences in system calls and executable file formats, requiring distinct versions of software for each platform. Their command-line interfaces provided comparable functions but varied syntactically—for example, file copying used PIP under CP/M-86 whereas DOS employed COPY.

Initially, MS-DOS and CP/M-86 operated on non-PC-compatible machines like Apricot and Sirius by adapting OS calls to specific hardware configurations. However, performance-sensitive applications often bypassed OS calls to directly access hardware on IBM PCs, resulting in faster execution on PC-specific software and encouraging adoption of hardware conforming to IBM PC standards. This standardization imposed a memory limit of 640 KB—earlier MS-DOS and CP/M-86 implementations could address nearly one megabyte before this limitation emerged.

Reception

PC Magazine observed that CP/M-86 "appears in several respects better suited for the PC" compared to DOS; nevertheless, its cost—being six times greater—deterred users who were not engaged in assembly language programming. The review underscored CP/M-86's advantages in areas where DOS underperformed, and vice versa, stressing that the extent of application compatibility would ultimately determine success. However, the absence of a run-time version for applications was considered a limitation for CP/M-86.

Versions

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

Operating System	BDOS Version	Release Date	Remarks
CP/M-86 1.0 for AST	Approximately 2.2	Circa 1981
CP/M-86 1.0 for Altos ACS 16000/8600	Approximately 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	Between 1981 and 1982
CompuView CP/M-86	Around 2.x	1982	Compatible with IBM PC hardware; supports disks up to 196 KB
IBM CP/M-86 for IBM PC Version 1.0	2.2	April 1982	Initial launch; disk capacity of 141 KB
IBM CP/M-86 for IBM PC Version 1.1	2.2	March 1983	Introduced support for hard drives
CP/M-86 Plus Version 3.1	3.1	October 1983	Designed for Apricot PC; multitasking kernel capable of managing four concurrent tasks
Personal CP/M-86 Version 1.0	3.1	November 1983	Targeted at Siemens PG685
Personal CP/M-86 Version 3.1	3.3	January 1985	For Apricot Computers F-Series; incorporated FAT file system support
Personal CP/M-86 Version 2.0	4.1	From 1986 onward	For 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 labeled as Personal CP/M-86 are derived from the CP/M-86 Plus codebase, indicating a shared lineage.

In addition, various East Bloc adaptations of CP/M-86 existed under designations such as SCP1700 (Single User Control Program), CP/K, and K8918-OS, developed by East-German companies like VEB Robotron Dresden and Energiekombinat Berlin, demonstrating localized implementations of the operating system.

Legacy

Since 1997, Caldera has authorized the distribution and modification of all original Digital Research files, including source code from the entire CP/M family, through Tim Olmstead's "The Unofficial CP/M Web site." Following Olmstead's passing in 2001, the free distribution license was renewed and extended by Lineo, then proprietor of Digital Research's intellectual property, on October 19, 2001.

External links

The Unofficial CP/M Website – authorized distributor of original Digital Research software
The comp.os.cpm FAQ
Intel iPDS-100 Using CP/M - Video