S5-DOS

Digital Research
Industry	Software, Operating systems
Founded	1974; 52 years ago
Founder	Gary Kildall
Products	CP/M-86, MP/M-86, Concurrent CP/M-86, Concurrent DOS, Multiuser DOS, FlexOS, DOS Plus, DR DOS
Website	www.cpunks.org/~almis/cpm/

CP/M-86 represents a now-obsolete iteration of the CP/M operating system, engineered by Digital Research (DR) for use with the Intel 8086 and Intel 8088 processors. It retained the command structure of CP/M-80 and employed the relocatable .CMD file format for its executable programs. Digital Research also developed a compatible multi-user multitasking system named MP/M-86, which later progressed into Concurrent CP/M-86. Incorporating a PC DOS compatibility layer, this evolved into Concurrent DOS, subsequently rebranded as Multiuser DOS, with the most recent release 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 encountered multiple postponements. When IBM was searching for an operating system for its IBM PC, CP/M-86 was favored due to CP/M’s vast software ecosystem. However, negotiations between Digital Research and IBM broke down because of disagreements over IBM’s non-disclosure agreement terms and its preference for a one-time payment instead of Digital Research’s royalty-based licensing. Following talks with Microsoft, IBM opted for 86-DOS (also known as QDOS), which Microsoft acquired, modified into MS-DOS, and licensed to IBM as PC DOS. After Digital Research founder Gary Kildall threatened legal action concerning intellectual property rights, IBM offered CP/M-86 as an alternative operating system option on the PC. Andy Johnson-Laird was responsible for creating most of the CP/M-86 BIOS drivers used on the IBM PC.

The IBM PC was introduced on 12 August 1981, shipping in October bundled with three operating systems: PC DOS, CP/M-86, and UCSD p-System. Digital Research launched CP/M-86 approximately six months after PC DOS in spring 1982; porting applications from CP/M-80 posed comparable challenges for both platforms. Additionally, in November 1981, Digital Research issued a version of CP/M-86 tailored for the proprietary IBM Displaywriter system.

Certain dual-processor systems combining 8-bit and 16-bit CPUs supported specialized CP/M-86 variants capable of running both CP/M-86 and CP/M-80 software. For instance, the DEC Rainbow operated CP/M-86/80, while CompuPro System 816 utilized CP/M 8-16. The Zenith Z-100 accommodated programs designed for its 8085 and 8088 processors.

As PC clones gained prominence, Microsoft widely licensed MS-DOS. Industry analysts observed that CP/M-86 and DOS were technically similar—CP/M-86 excelled in memory management whereas DOS offered superior speed. BYTE magazine speculated that Microsoft's decision to reserve multitasking capabilities for Xenix created an opportunity for Concurrent CP/M-86.

Despite this, CP/M-86 suffered poor sales on the IBM PC due to its $240 price point compared to $40 for PC DOS; 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 combined backing from IBM, Microsoft, and Lifeboat posed a significant challenge to CP/M-86’s market position; commentator Jerry Pournelle attributed some of Digital Research’s struggles to ineffective marketing.

By early 1983, Digital Research began selling CP/M-86 version 1.1 directly to consumers at $60 per copy, promoting it as providing access to the largest available software library and bundling Graphics System Extension (GSX), previously priced at $75. The company also initiated retail distribution of CP/M-86 applications and announced in May 1983 that all its programming languages and utilities would be available in DOS versions—acknowledging PC DOS’s dominant market share but denying that this influenced their decision. Early in 1984, promotions included complimentary Concurrent CP/M-86 copies bundled with application purchases; these applications were delivered on self-booting disks that did not require loading the OS first. In January 1984, Digital Research introduced Kanji CP/M-86 aimed at nine Japanese corporations including Mitsubishi Electric and Sanyo; later Fujitsu released FM-16 computers running Kanji CP/M-86.

Although both CP/M-86 and DOS provided comparable capabilities, they were incompatible because of differences in system calls and executable file formats, necessitating distinct software versions for each platform. Their command-line interfaces performed similar tasks but used different syntax—for example, copying files utilized PIP TARGET=SOURCE under CP/M compared to COPY SOURCE TARGET in DOS.

Initially, MS-DOS and CP/M-86 operated on non-PC-compatible hardware such as Apricot and Sirius systems by adapting OS calls to specific hardware configurations. Nevertheless, performance-sensitive applications bypassed the OS to access IBM PC hardware directly, resulting in faster execution on PC-specific machines. This trend encouraged widespread adoption of PC-compatible architectures that imposed a memory limit of 640 KB; early MS-DOS and CP/M-86 systems did not have this restriction and could address nearly one megabyte of RAM.

Reception

PC Magazine observed that CP/M-86 appeared to be "better suited to the PC" in multiple aspects 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 was less capable and vice versa, stressing that the extent of application compatibility would ultimately influence its market acceptance. A significant limitation was CP/M-86's absence of a run-time version for software applications.

Versions

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

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	Supported 196 KB disk capacity; compatible with IBM PC hardware
IBM CP/M-86 for the IBM Personal Computer Version 1.0	2.2	April 1982	Initial launch; supported 141 KB disk capacity
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 the Apricot PC; included multitasking kernel enabling 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	Targeted Apricot Computers F-Series; incorporated FAT disk compatibility used by DOS
Personal CP/M-86 Version 2.0	4.1	From 1986 onward	For Siemens PC16-20; shared BDOS kernel with DOS Plus 1.2
Personal CP/M-86 Version 2.11	4.1	From 1986 onward	Designed for Siemens PG685

All Personal CP/M-86 variants trace their origins to CP/M-86 Plus, reflecting their derivation from its codebase.

There were also several Eastern Bloc adaptations of CP/M-86, known under titles such as SCP1700 (Single User Control Program), CP/K, and K8918-OS, developed by East German companies VEB Robotron Dresden and Energiekombinat Berlin.

Legacy

Starting in 1997, Caldera granted permission to redistribute and modify all original Digital Research materials, including source code from the CP/M family, through Tim Olmstead's "The Unofficial CP/M Web site." Following Olmstead's passing in 2001, Lineo, then the proprietor of Digital Research assets, renewed and broadened this free distribution license later that 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