CP/M-86/80
| Industry | Software |
|---|---|
| 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 processors. It maintained compatibility with CP/M-80 by using identical system commands, while executable files employed the relocatable .CMD file format. Digital Research also engineered a multi-user, multitasking operating system compatible with CP/M-86, known as MP/M-86, which later evolved into Concurrent CP/M-86. Following the integration of a PC DOS compatibility emulator, this platform was renamed Concurrent DOS and subsequently rebranded as Multiuser DOS, with its latest iteration being REAL/32. The operating systems FlexOS, DOS Plus, and DR DOS trace their origins back to Concurrent DOS.
History
Initially slated for release in November 1979, Digital Research's CP/M-86 experienced multiple postponements. When IBM sought an operating system for its forthcoming IBM PC, CP/M-86 was considered the primary candidate due to CP/M’s extensive software ecosystem. However, negotiations between IBM and Digital Research faltered over disagreements regarding IBM's non-disclosure agreement and its preference for a one-time payment instead of Digital Research’s proposed royalty-based model.
Consequently, IBM partnered with Microsoft, which had acquired 86-DOS (also known as QDOS) from Seattle Computer Products. Microsoft adapted this into MS-DOS and licensed it to IBM under the name PC DOS. Upon discovering this development, Digital Research founder Gary Kildall threatened legal action over alleged intellectual property infringement, prompting IBM to offer CP/M-86 as an alternative operating system option on the IBM PC. Andy Johnson-Laird was responsible for developing most of the BIOS drivers required for CP/M-86 on the IBM PC.
The IBM PC was launched in August 1981 and became available in October with three operating system choices: PC DOS, CP/M-86, and UCSD p-System. Digital Research's CP/M-86 was released approximately six months after PC DOS, arriving in spring 1982. Transitioning applications from CP/M-80 to either platform presented similar challenges. Additionally, in November 1981, Digital Research introduced a version tailored for the proprietary IBM Displaywriter.
Certain dual-processor systems combining 8-bit and 16-bit architectures supported specialized versions of CP/M-86 capable of running both CP/M-80 and CP/M-86 software. For instance, the DEC Rainbow utilized CP/M-86/80, while the CompuPro System 816 operated CP/M 8-16. The Zenith Z-100 was capable of executing programs designed for both its 8085 and 8088 CPUs.
As PC clones gained popularity, Microsoft extensively licensed MS-DOS. Technical evaluations revealed that although CP/M-86 offered superior memory management capabilities compared to DOS, it lagged behind in speed. BYTE magazine observed that Microsoft's focus on multitasking through Xenix created an opportunity for Concurrent CP/M-86.
However, with a price point of $240 per license versus $40 for PC DOS, CP/M-86 sales were significantly lower; surveys indicated that 96.3% of IBM PCs shipped with DOS, while only 3.4% included CP/M-86 or Concurrent CP/M-86. By mid-1982, Lifeboat Associates—a leading vendor of CP/M software—shifted its support toward DOS. BYTE cautioned that this alliance posed a substantial threat to the future viability of CP/M-86, while analyst Jerry Pournelle criticized Digital Research’s ineffective marketing strategies.
In early 1983, Digital Research began selling version 1.1 of CP/M-86 directly to consumers at a reduced price of $60 per copy. This edition was promoted as providing access to the largest professional software library and bundled Graphics System Extension (GSX), previously sold separately for $75. The company also expanded its distribution network through retail outlets. By May 1983, Digital Research announced DOS-compatible versions of all its programming languages and utilities, acknowledging PC DOS’s market dominance but denying that this influenced their product decisions.
In early 1984, Digital Research offered complimentary copies of Concurrent CP/M-86 with the purchase of two CP/M-86 applications; these applications were distributed on self-booting disks that did not require prior loading of the operating system. That same January marked the introduction of Kanji CP/M-86—a Japanese-language variant developed collaboratively with nine Japanese corporations including Mitsubishi Electric and Sanyo Electric—with Fujitsu releasing FM-16-based hardware running this OS before year-end.
Although CP/M-86 and DOS provided comparable functionalities, they were incompatible due to differences in system calls and file formats; consequently, software had to be developed separately for each environment. Their command-line interfaces were functionally similar but syntactically distinct—for example, copying files used PIP TARGET=SOURCE under CP/M versus COPY SOURCE TARGET in DOS.
At first, MS-DOS and CP/M-86 operated on non-PC-compatible machines such as Apricot and Sirius computers by adapting OS calls to specific hardware configurations. Nevertheless, performance-critical software frequently bypassed operating system calls in favor of direct hardware manipulation—particularly in gaming—resulting in better performance on genuine IBM PC hardware. This trend encouraged market adoption toward fully IBM PC–compatible systems but imposed a memory limitation of 640 KB; earlier computers without this constraint could access nearly one megabyte of RAM.
Reception
According to PC Magazine, CP/M-86 appeared to be more suitably designed for the PC in several respects compared to DOS; nonetheless, its significantly higher cost—approximately six times that of DOS—deterred users who were not engaged in assembly language programming. CP/M-86 demonstrated strengths in areas where DOS was less capable, and the reverse was also true, with the breadth of application support serving as a decisive factor. A significant limitation of CP/M-86 was the absence of a run-time version for software applications.
Versions
CP/M-86 releases are identified by two version numbers: one indicating the overall operating system (displayed during startup) and another representing the BDOS kernel version. The following versions are documented:
| Operating System | BDOS Version | Release Date | Remarks |
|---|---|---|---|
| CP/M-86 1.0 for AST Research | 2.2? | Circa 1981 | |
| CP/M-86 1.0 for Altos Computer Systems ACS 16000/ACS 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 | Approximately 2.x | 1982 | Disk capacity of 196 KB; compatible with IBM PC hardware |
| IBM CP/M-86 for IBM Personal Computer Version 1.0 | 2.2 | April 1982 | Initial launch; supported disks with 141 KB capacity |
| IBM CP/M-86 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 handling up to 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 F-Series; incorporated FAT disk compatibility aligned with DOS |
| 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 | For Siemens PG685 |
All Personal CP/M-86 editions cite CP/M-86 Plus as their origin, signifying derivation from that codebase.
In addition, several Eastern Bloc adaptations existed under various designations such as SCP1700, CP/K, and K8918-OS, developed by East German companies including VEB Robotron Dresden and Energiekombinat Berlin, illustrating localized versions of the CP/M-86 platform.
Legacy
Starting in 1997, Caldera permitted the redistribution and modification of all original Digital Research files—including the CP/M source code—through Tim Olmstead's "The Unofficial CP/M Web site". Following Olmstead's passing in 2001, the free distribution license was renewed and expanded on October 19, 2001, by Lineo, then proprietor of Digital Research assets.
See also
Further reading
- The Byte Guide to CP/M-86 authored by Mark Dahmke (1984, McGraw-Hill, ISBN 978-0-07-015072-0)
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