CP/M-86 Plus

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

CP/M-86 represents a discontinued iteration of the CP/M operating system developed by Digital Research (DR) specifically for the Intel 8086 and Intel 8088 CPU architectures. It maintained compatibility with CP/M-80's command set, utilizing relocatable executables in the .CMD file format. Digital Research also engineered a multitasking, multi-user system compatible with CP/M-86 called MP/M-86, which later evolved into Concurrent CP/M-86. By integrating PC DOS compatibility through an emulator, this system was rebranded as Concurrent DOS, which subsequently became Multiuser DOS, with its latest iteration known as REAL/32. The operating systems FlexOS, DOS Plus, and DR DOS trace their origins back to Concurrent DOS.

History

Although Digital Research announced CP/M-86 in November 1979, its release encountered several postponements. When IBM sought an operating system for its forthcoming IBM PC, CP/M-86 was initially favored because of its extensive software ecosystem. Nevertheless, negotiations faltered due to IBM's insistence on a non-disclosure agreement and preference for a one-time payment rather than Digital Research's royalty-based pricing. Subsequently, after discussions with Microsoft, IBM opted for 86-DOS (QDOS), which Microsoft had acquired from Seattle Computer Products; Microsoft adapted it into MS-DOS and licensed it to IBM as PC DOS. In response, Digital Research founder Gary Kildall threatened legal action concerning intellectual property rights, prompting IBM to offer CP/M-86 as an alternative OS option for the IBM PC. Andy Johnson-Laird was responsible for developing most of the BIOS drivers required for CP/M-86 on the IBM PC platform.

The IBM PC was launched on August 12, 1981, with shipments beginning in October; it initially supported three operating systems: PC DOS, CP/M-86, and UCSD p-System. Digital Research released CP/M-86 approximately six months after PC DOS in early 1982. Porting applications from CP/M-80 presented similar challenges for both operating systems. Additionally, in November 1981, Digital Research introduced a version of CP/M-86 tailored for the proprietary IBM Displaywriter system.

Certain dual-processor machines combining 8-bit and 16-bit CPUs ran specialized CP/M-86 variants capable of executing both CP/M-80 and CP/M-86 software natively. For example, the DEC Rainbow operated CP/M-86/80; CompuPro System 816 supported CP/M 8-16; and the Zenith Z-100 could run programs designed for its 8085 and 8088 processors.

As PC clones gained popularity, Microsoft broadly licensed MS-DOS. Technical analyses found that CP/M-86 and DOS were comparable—CP/M-86 offered more advanced memory management while DOS provided superior speed. BYTE magazine observed that Microsoft's multitasking capabilities were reserved for Xenix, leaving an opportunity for Concurrent CP/M-86.

Despite this, CP/M-86’s retail price of $240 per license contrasted sharply with PC DOS’s $40 price point, resulting in significantly lower sales; surveys indicated that 96.3% of IBM PCs shipped with DOS compared to only 3.4% running CP/M-86 or Concurrent CP/M-86. By mid-1982, Lifeboat Associates—a key distributor of CP/M software—shifted its support toward DOS products. BYTE cautioned that this combined momentum threatened CP/M-86’s market viability, with commentator Jerry Pournelle attributing part of Digital Research’s difficulties to marketing shortcomings.

By early 1983, Digital Research began selling version 1.1 of CP/M-86 directly to end users at $60, promoting it as providing immediate access to a broad software library and bundling the Graphics System Extension (GSX), previously sold separately for $75. The company also expanded distribution through retail outlets. In May 1983, DRI announced DOS-compatible versions of its programming languages and utilities; while acknowledging PC DOS’s dominance in the market, they denied that this influenced their decision to develop these versions. Early in 1984, promotions included complimentary Concurrent CP/M-86 copies bundled with purchases of two CP/M-86 applications; these came as self-booting disks that did not require loading the operating system first.

In January 1984, Digital Research launched Kanji CP/M-86—a Japanese-language version developed collaboratively with nine Japanese corporations including Mitsubishi Electric and Sanyo Electric. By December that year, Fujitsu announced FM-16 series computers running Kanji CP/M-86.

While CP/M-86 and DOS shared similar functions, they remained incompatible because of differences in system calls and executable formats; consequently, separate software versions were necessary for each OS. Their command line interfaces offered comparable capabilities but employed distinct syntax—for instance, file copying used PIP under CP/M versus COPY under DOS.

Initially, MS-DOS and CP/M-86 operated on non-PC-compatible systems such as Apricot and Sirius by adapting OS calls to specific hardware configurations. However, performance-critical software often bypassed OS calls entirely to access IBM PC hardware directly—this resulted in superior performance from PC-specific applications compared to their counterparts on other platforms. This trend accelerated widespread adoption of PC-compatible hardware architectures but imposed a memory ceiling of 640 KB; early MS-DOS and CP/M-86 systems did not have this limitation and could utilize nearly one megabyte of RAM.

Reception

PC Magazine observed that CP/M-86 appeared, in multiple respects, to be more suitably designed 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 showed weaknesses and vice versa, stressing that the breadth of application compatibility would ultimately determine success. A notable limitation was CP/M-86’s absence of a run-time version for 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 BDOS kernel. Important editions 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	1981/1982
CompuView CP/M-86	Around 2.x	1982	Featured 196 KB disk capacity; compatible with IBM PC hardware
IBM CP/M-86 for IBM Personal Computer Version 1.0	2.2	April 1982	Initial launch; supported 141 KB disk capacity
IBM CP/M-86 Version 1.1	2.2	March 1983	Introduced hard disk support
CP/M-86 Plus Version 3.1	3.1	October 1983	Designed for Apricot PC, incorporated multitasking kernel managing 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	Targeted at Apricot F-Series; added FAT filesystem compatibility
Personal CP/M-86 Version 2.0	4.1	From 1986 onwards	Developed for Siemens PC16-20, shared BDOS with DOS Plus 1.2
Personal CP/M-86 Version 2.11	4.1	From 1986 onwards	Intended for Siemens PG685

All variants under the Personal CP/M-86 label are derived from the CP/M-86 Plus source code.

In addition, various Eastern Bloc adaptations existed, bearing titles such as SCP1700 (Single User Control Program), CP/K, and K8918-OS, produced by East German companies like VEB Robotron Dresden and Energiekombinat Berlin.

Legacy

Since 1997, Caldera has permitted redistribution and modification of all original Digital Research files—including source code linked to the CP/M family—through Tim Olmstead’s "The Unofficial CP/M Web site." Following Olmstead’s passing on September 12, 2001, the free distribution license was renewed and extended by Lineo, then the proprietor 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
Intel iPDS-100 Using CP/M Video