SCP.SYS
| 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 was a version of the CP/M operating system developed by Digital Research (DR) specifically for the Intel 8086 and Intel 8088 CPUs, which has since been discontinued. It preserved the command set of CP/M-80 and employed relocatable executables in the .CMD file format. Digital Research also developed MP/M-86, a multi-user multitasking system compatible with CP/M-86, which later evolved into Concurrent CP/M-86. With added PC DOS compatibility, this product was rebranded as Concurrent DOS, eventually becoming Multiuser DOS, whose most recent iteration is REAL/32. The operating systems FlexOS, DOS Plus, and DR DOS trace their origins back to Concurrent DOS.
History
Although initially slated for release in November 1979, Digital Research's CP/M-86 experienced several postponements. IBM, searching for an operating system for its new PC, initially favored CP/M-86 due to its robust software ecosystem. However, negotiations broke down over IBM's insistence on a non-disclosure agreement and preference for a one-time licensing fee, conflicting with Digital Research's royalty-based model. Subsequently, IBM engaged Microsoft and opted for Microsoft’s 86-DOS (also known as QDOS), which was rebranded as MS-DOS and licensed to IBM as PC DOS. Following this, Gary Kildall, founder of Digital Research, threatened legal action over alleged intellectual property violations, prompting IBM to offer CP/M-86 as an alternative operating system for the PC. The majority of CP/M-86 BIOS drivers for the IBM PC were created by Andy Johnson-Laird.
When the IBM PC launched in August 1981, it came with three operating system choices: PC DOS, CP/M-86, and UCSD p-System. Digital Research introduced CP/M-86 six months after PC DOS, in spring 1982. Porting applications between CP/M-80 and either of these systems was similarly complex. Additionally, a version tailored for the IBM Displaywriter was released in November 1981.
Some dual-processor machines combining 8-bit and 16-bit CPUs offered specialized CP/M-86 versions capable of running both CP/M-86 and CP/M-80 software. Examples include the DEC Rainbow with CP/M-86/80 support and the CompuPro System 816 running CP/M 8-16. The Zenith Z-100 could execute programs designed for both 8085 and 8088 processors.
As clone PCs proliferated, Microsoft widely licensed MS-DOS. Industry experts generally considered CP/M-86 and DOS to be technically comparable; while CP/M-86 provided superior memory management capabilities, DOS typically delivered faster performance. BYTE magazine observed that reserving multitasking features exclusively for Xenix created a niche for Concurrent CP/M-86.
Despite these technical merits, CP/M-86’s $240 price tag per copy—compared to $40 for PC DOS on the IBM PC—resulted in poor sales; approximately 96.3% of IBM PCs shipped with DOS, while only about 3.4% included CP/M-86 or Concurrent CP/M-86. By mid-1982, leading software publishers such as Lifeboat Associates shifted their focus toward DOS. BYTE and other industry commentators criticized Digital Research’s marketing approach.
By early 1983, Digital Research began selling version 1.1 of CP/M-86 directly to customers at $60 per copy, promoting it as granting access to the largest collection of business and educational software titles and featuring Graphics System Extension (GSX). The company also expanded distribution through third-party retailers. In May 1983, Digital Research announced plans to release DOS-compatible versions of its programming languages and utilities, acknowledging DOS’s market dominance but denying that this move was due to shortcomings in CP/M-86’s performance. By early 1984, DRI bundled free copies of Concurrent CP/M-86 with purchases of two CP/M-86 applications and marketed self-booting disks that eliminated the need to load the OS separately.
In January 1984, Digital Research launched Kanji CP/M-86—a Japanese-language edition—developed in collaboration with nine Japanese companies including Mitsubishi Electric and Sanyo. Later that year Fujitsu introduced FM-16 models running Kanji CP/M-86.
Although CP/M-86 and DOS offered similar capabilities, they were incompatible because of differences in system calls and executable file formats; consequently, software had to be developed independently for each platform. Their command-line interfaces provided analogous functions but differed in syntax—for instance, copying files required PIP TARGET=SOURCE on CP/M compared to COPY SOURCE TARGET on DOS.
Initially both MS-DOS and CP/M-86 operated on some hardware not fully compatible with the IBM PC architecture (such as Apricot and Sirius), aiming to achieve hardware independence through standardized system calls adapted to individual machines. Nonetheless, performance-sensitive applications frequently accessed IBM PC hardware directly for speed benefits, which contributed to widespread adoption of PC-compatible hardware standards. This standardization imposed a memory limit of 640 KB; earlier MS-DOS and CP/M-86 systems without this constraint could address nearly one megabyte of RAM.
Reception
PC Magazine observed that CP/M-86 appeared to be more suitably designed for the PC in several respects compared to DOS; nevertheless, its cost—being six times greater—deterred users who did not engage in assembly language programming. The review underscored CP/M-86's advantages where DOS showed limitations and vice versa, stressing that the extent of application availability would ultimately determine success, while noting the absence of a run-time version for CP/M-86 applications as a significant disadvantage.
Versions
CP/M-86 releases are identified by two version numbers: one representing the entire operating system (displayed during startup) and another designating the BDOS kernel version. Key iterations include:
| Operating System | BDOS Version | Release Date | Remarks |
|---|---|---|---|
| CP/M-86 1.0 tailored for AST Research | approximately 2.2 | circa 1981 | |
| CP/M-86 1.0 for Altos Computer Systems ACS 16000/8600 | approximately 2.2 | November 1981 | |
| CP/M-86 Version 1.1 used on IBM Displaywriter | 2.2 | November 1981 | |
| CP/M-86 1.0 for Sirius 1/Victor 9000 systems | 2.2a | 1981/1982 timeframe | |
| CompuView CP/M-86 | around 2.x | 1982 | Compatible with IBM PC hardware; supports disks up to 196 KB |
| IBM CP/M-86 for IBM PC Version 1.0 | 2.2 | April 1982 | Initial launch; disk capacity of 141 KB |
| IBM CP/M-86 for IBM PC Version 1.1 | 2.2 | March 1983 | Introduced hard drive compatibility |
| CP/M-86 Plus Version 3.1 | 3.1 | October 1983 | Developed for Apricot PC; multitasking kernel enabling up to four concurrent tasks |
| Personal CP/M-86 Version 1.0 | 3.1 | November 1983 | Designed for Siemens PG685 |
| Personal CP/M-86 Version 3.1 | 3.3 | January 1985 | For Apricot F-Series; incorporated support for FAT-formatted disks compatible with DOS |
| Personal CP/M-86 Version 2.0 | 4.1 | From 1986 onward | Intended 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 model |
All Personal CP/M-86 editions reference the CP/M-86 Plus variant, indicating their derivation from its underlying code.
Several Eastern Bloc adaptations of CP/M-86 were developed under various designations such as SCP1700 (Single User Control Program), CP/K, and K8918-OS by East German manufacturers VEB Robotron located in Dresden and Berlin.
Legacy
Since 1997, Caldera has authorized the redistribution and modification of all original Digital Research materials, including the CP/M source code, through Tim Olmstead's "The Unofficial CP/M Web site." Following Olmstead’s passing in September 2001, Lineo—then the proprietor of Digital Research assets—renewed and expanded this free distribution license in October of the same year.
See also
Further reading
- The Byte Guide to CP/M-86 by Mark Dahmke, McGraw-Hill, 1984, 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