SCP1700

Digital Research

Industry	Software, Operating systems
Founded	1974 (1974)
Founder	Gary Kildall
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 represents a now-obsolete variant of the CP/M operating system, engineered by Digital Research (DR) specifically for the Intel 8086 and Intel 8088 CPU architectures. It preserved the command set familiar from CP/M-80 and employed the relocatable .CMD file format for its executable files. Digital Research also developed a multitasking, multi-user operating system compatible with CP/M-86, known as MP/M-86, which later evolved into Concurrent CP/M-86. Incorporating an emulator for PC DOS compatibility, this system was renamed Concurrent DOS, subsequently rebranded as Multiuser DOS, with its most recent iteration called REAL/32. Additional operating systems such as FlexOS, DOS Plus, and DR DOS trace their origins back to Concurrent DOS.

History

Digital Research originally announced CP/M-86 in November 1979, but its release was postponed multiple times. When IBM required an operating system for the IBM PC, CP/M-86 was favored because of its broad software support. Nevertheless, negotiations between Digital Research and IBM broke down due to IBM’s insistence on a non-disclosure agreement and a single payment model, conflicting with DRI’s preference for royalties. Consequently, IBM partnered with Microsoft, who licensed and modified 86-DOS (QDOS) from Seattle Computer Products into MS-DOS and marketed it as PC DOS. After Digital Research’s founder Gary Kildall threatened legal action over alleged intellectual property violations, IBM offered CP/M-86 as an alternative OS option on the PC. The majority of CP/M-86 BIOS drivers for the IBM PC were crafted by Andy Johnson-Laird.

The IBM PC debuted on August 12, 1981, with shipments starting in October that year, providing three operating system choices: PC DOS, CP/M-86, and UCSD p-System. Digital Research launched CP/M-86 approximately six months following PC DOS in early 1982; porting applications from CP/M-80 proved similarly complex for both platforms. Additionally, a version tailored for the proprietary IBM Displaywriter was released in November 1981.

Certain specialized editions of CP/M-86 supported dual-processor configurations combining 8-bit and 16-bit CPUs, including CP/M-86/80 for the DEC Rainbow and CP/M 8-16 designed for the CompuPro System 816. The Zenith Z-100 variant accommodated programs written for both 8085 and 8088 processors.

As PC clones gained popularity, Microsoft expanded MS-DOS licensing extensively. Industry observers noted that while CP/M-86 offered superior memory management capabilities, DOS delivered faster execution speeds. BYTE magazine suggested that Microsoft’s focus on Xenix multitasking left market space open for Concurrent CP/M-86.

Nonetheless, priced at $240 per license compared to PC DOS’s $40, CP/M-86 experienced poor sales; surveys indicated that over 96% of IBM PCs shipped with DOS installed. Lifeboat Associates, a leading distributor of CP/M software, shifted their emphasis to DOS support by mid-1982. BYTE cautioned that the combined backing of IBM, Microsoft, and Lifeboat posed a significant threat to CP/M-86’s viability. Analyst Jerry Pournelle criticized Digital Research’s approach to marketing.

By early 1983, Digital Research offered CP/M-86 version 1.1 directly to customers at $60 per copy, highlighting access to an extensive software ecosystem and bundling the Graphics System Extension (GSX). The company broadened retail distribution channels and announced plans by May 1983 to release DOS-compatible versions of its programming languages and utilities—acknowledging DOS's market leadership but denying it influenced their strategy. Early in 1984 promotions included complimentary copies of Concurrent CP/M-86 with application purchases and self-booting disks that bypassed loading CP/M-86 initially. In January 1984, DRI introduced Kanji CP/M-86 aimed at nine Japanese corporations such as Mitsubishi Electric and Sanyo; Fujitsu subsequently launched FM-16 models utilizing this operating system.

While both CP/M-86 and DOS provided comparable features, they were incompatible due to differing system calls and file formats, necessitating distinct software versions. Their command-line interfaces varied in syntax despite functional parallels.

Initially, MS-DOS and CP/M-86 operated on non-PC-compatible hardware platforms like Apricot and Sirius by adapting OS calls to specific hardware configurations. However, performance-sensitive applications often circumvented OS calls to interact directly with IBM PC hardware components—resulting in faster execution on PC-specific programs. This trend contributed to standardizing hardware around the IBM PC design, which imposed a conventional memory limit of 640 KB—a constraint absent in early MS-DOS or CP/M-86 systems capable of addressing 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 cost—approximately six times that of DOS—deterred users who were not engaged in assembly language programming. The review underscored areas where CP/M-86 excelled relative to DOS and where DOS outperformed CP/M-86, concluding that the extent of application software availability would ultimately influence its market acceptance. A significant limitation identified was the absence of a run-time version for CP/M-86 applications.

Versions

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

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	Supported IBM PC compatible hardware with 196 KB disk capacity
IBM CP/M-86 Version 1.0 for IBM Personal Computer	2.2	April 1982	Initial launch featuring a disk capacity of 141 KB
IBM CP/M-86 Version 1.1	2.2	March 1983	Introduced support for hard disk drives
CP/M-86 Plus Version 3.1	3.1	October 1983	Designed for Apricot PC, included multitasking kernel allowing up to four concurrent tasks
Personal CP/M-86 Version 1.0	3.1	November 1983	Released on Siemens PG685
Personal CP/M-86 Version 3.1	3.3	January 1985	For Apricot F-Series, added compatibility with FAT-formatted disks used by DOS
Personal CP/M-86 Version 2.0	4.1	Post-1986	Targeted Siemens PC16-20, shared BDOS kernel with DOS Plus 1.2
Personal CP/M-86 Version 2.11	4.1	Post-1986	For Siemens PG685

All variants under the Personal CP/M-86 label are based on the CP/M-86 Plus codebase, indicating a common lineage.

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

Legacy

Starting in 1997, Caldera authorized the distribution and modification of 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 holding ownership of these Digital Research assets, renewed and broadened the free distribution license later that year.

Further reading

• The Byte Guide to CP/M-86 authored by Mark Dahmke (1984), published by McGraw-Hill, ISBN 978-0-07-015072-0

External links

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