K8918-OS

Digital Research
Industry	Software, Operating systems
Founded	1974
Founder	Gary Kildall
Products	CP/M-86, MP/M-86, Concurrent CP/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 created by Digital Research (DR) for use with the Intel 8086 and Intel 8088 CPUs. It maintained compatibility with CP/M-80 commands, utilizing the relocatable .CMD file format for executable files. Digital Research also developed a multitasking, multi-user OS compatible with CP/M-86 known as MP/M-86, which later evolved into Concurrent CP/M-86. By incorporating an emulator enabling PC DOS compatibility, this platform was rebranded as Concurrent DOS and subsequently evolved into Multiuser DOS, whose most recent edition is REAL/32. The operating systems FlexOS, DOS Plus, and DR DOS all trace their origins back to Concurrent DOS.

History

Originally slated for release in November 1979, Digital Research's CP/M-86 experienced multiple postponements. When IBM sought an operating system for the upcoming IBM PC, CP/M-86 was initially favored due to its broad software ecosystem. However, negotiations broke down because of IBM’s insistence on a non-disclosure agreement and a one-time payment demand, conflicting with Digital Research’s preference for royalties. As a result, IBM turned to Microsoft, which licensed and modified 86-DOS (also known as QDOS) from Seattle Computer Products, marketing it as MS-DOS and selling it under the name PC DOS. Upon discovering this arrangement, Digital Research founder Gary Kildall threatened to pursue legal action over alleged intellectual property violations, prompting IBM to offer CP/M-86 as an alternative operating system. The majority of CP/M-86 BIOS drivers for the IBM PC were authored by Andy Johnson-Laird.

The IBM PC debuted on August 12, 1981, and by October was available with three operating system choices: PC DOS, CP/M-86, and the UCSD p-System. Digital Research launched CP/M-86 approximately six months after PC DOS in early 1982. Transitioning applications from CP/M-80 to either OS presented similar levels of difficulty. Additionally, in November 1981, Digital Research released a version designed for the proprietary IBM Displaywriter.

Certain dual-processor machines combining 8-bit and 16-bit architectures operated specialized variants of CP/M-86 that supported both CP/M-80 and CP/M-86 software. For instance, the DEC Rainbow utilized CP/M-86/80, while the ran CP/M 8-16. The Zenith Z-100 was capable of running programs intended for both its 8085 and 8088 processors.

As PC clones gained popularity, Microsoft widely licensed MS-DOS. Industry experts observed that MS-DOS and CP/M-86 were technically comparable; although CP/M-86 offered better memory management capabilities, DOS delivered faster performance. BYTE noted that Microsoft’s emphasis on multitasking through Xenix left room in the market for systems like Concurrent CP/M-86.

Commercially, CP/M-86 struggled on the IBM PC platform due to its relatively steep pricing— per license compared to for PC DOS. Market surveys indicated that over 96% of IBM PCs shipped with DOS installed, whereas fewer than 4% utilized CP/M-86 or Concurrent CP/M-86. By mid-1982, major software distributor Lifeboat Associates had shifted its support exclusively to DOS. BYTE cautioned that this partnership posed a significant threat to CP/M-86’s viability, with analysts attributing difficulties largely to Digital Research’s ineffective marketing strategies.

By early 1983, Digital Research was selling version 1.1 of CP/M-86 directly to end users at , promoting access to an extensive catalog of business and educational applications and bundling Graphics System Extension (GSX). The company broadened its distribution through retail outlets and in May 1983 announced plans to release DOS-compatible versions of its programming languages and utilities—acknowledging DOS’s market dominance while denying it influenced their decision-making process. In early 1984, Digital Research offered complimentary copies of Concurrent CP/M-86 with purchases of two CP/M-86 software titles and marketed self-booting disks that eliminated the need to load the OS separately.

In January 1984, Digital Research launched Kanji CP/M-86 aimed at Japanese corporations such as Mitsubishi Electric Corporation, Sanyo Electric Co. Ltd., and Sord Computer Corp.. Later that year, Fujitsu introduced FM-16 computers running Kanji CP/M-86.

Although functionally similar, CP/M-86 and DOS were incompatible due to differing system call interfaces and executable file formats, necessitating distinct software versions for each platform. Their command-line interfaces also varied syntactically despite offering analogous functionalities.

Initially, both MS-DOS and CP/M-86 operated on non-PC-compatible hardware like those from Apricot and Sirius, aiming to deliver hardware-independent applications through standardized system calls customized per device. However, performance-sensitive programs frequently accessed IBM PC hardware directly to optimize speed—especially in graphics-intensive games—leading to widespread adoption of PC-compatible hardware standards. This standardization imposed a memory ceiling of 640 KB, unlike early MS-DOS and CP/M-86 systems which could address nearly one megabyte of RAM.

Reception

PC Magazine observed that CP/M-86 appeared to be "better suited to the PC" than DOS in multiple respects; nevertheless, its cost—being six times greater—deterred users who did not primarily engage in assembly language programming. The review underscored CP/M-86's advantages where DOS showed limitations, and conversely, highlighting that the extent of application compatibility would ultimately determine success. A significant drawback identified was the absence of a run-time module for applications in CP/M-86.

Versions

CP/M-86 releases are denoted by two version numbers: one representing the overall operating system (displayed during startup) and another for the BDOS kernel. Important iterations include:

Operating System	BDOS Version	Release Date	Remarks
CP/M-86 1.0 tailored for AST Research	2.2?	Circa 1981
CP/M-86 1.0 for Altos Computer Systems ACS 16000/8600	2.2?	November 1981
CP/M-86 Version 1.1 used by IBM Displaywriter	2.2	November 1981
CP/M-86 1.0 for Sirius 1/Victor 9000	2.2a	1981/1982
CompuView CP/M-86	Approx. 2.x	1982	Disk capacity of 196 KB; compatible with IBM PC hardware
IBM CP/M-86 for IBM PC Version 1.0	2.2	April 1982	Initial launch; supported 141 KB disks
IBM CP/M-86 for IBM PC 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, featuring a multitasking kernel capable of managing up to four concurrent tasks
Personal CP/M-86 Version 1.0	3.1	November 1983	Released specifically for Siemens PG685
Personal CP/M-86 Version 3.1	3.3	January 1985	For Apricot Computers F-Series; incorporated FAT-formatted disk compatibility used by DOS
Personal CP/M-86 Version 2.0	4.1	From 1986 onward	Developed for Siemens PC16-20, sharing BDOS with DOS Plus 1.2
Personal CP/M-86 Version 2.11	4.1	From 1986 onward	Targeted Siemens PG685

All versions under Personal CP/M-86 derive from the CP/M-86 Plus codebase, as indicated by their references.

In addition, several Eastern Bloc adaptations of CP/M-86 were developed under different names such as SCP1700 (Single User Control Program), CP/K, and K8918-OS, produced by East German companies including VEB Robotron Dresden and Energiekombinat Berlin.

Legacy

Since 1997, Caldera has permitted redistribution and modification of all original Digital Research files, including source code related to the CP/M family, through Tim Olmstead's "The Unofficial CP/M Web site." Following Olmstead’s passing in September 2001, this free distribution license was extended and enhanced by Lineo, then custodian of these Digital Research assets, in October of the same year.

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