CP/M-86 was a version of the CP/M operating system that Digital Research (DR) made for the Intel 8086 and Intel 8088. The system commands are the same as CP/M-80. Executable files used the relocatable .CMD file format (the same filename extension .CMD is used by Microsoft Windows for unrelated batch files). Digital Research also produced a multi-user multitasking operating system compatible with CP/M-86, MP/M-86, which later evolved into Concurrent CP/M-86. When an emulator was added to provide PC DOS compatibility, the system was renamed Concurrent DOS, which later became Multiuser DOS. The DOS Plus, FlexOS, and DR DOS families of operating systems started as derivations of Concurrent DOS.
When IBM contacted other companies to obtain components for the IBM PC, the as-yet unreleased CP/M-86 was its first choice for an operating system because CP/M had the most applications at the time. Negotiations between Digital Research and IBM quickly deteriorated over IBM's non-disclosure agreement and its insistence on a one-time fee rather than DRI's usual royalty licensing plan. After discussions with Microsoft, IBM decided to use 86-DOS (QDOS), a CP/M-like operating system that Microsoft bought from Seattle Computer. Microsoft adapted it for PC, and licensed it to IBM. It was sold by IBM under the name of PC DOS. When PC-clones came about, other companies sold it under the name of MS-DOS. After learning about the deal, Digital Research founder Gary Kildall threatened to sue IBM for infringing DRI's intellectual property, and IBM agreed to offer CP/M-86 as an alternative operating system on the PC to settle the claim.
CP/M-86 was one of three operating systems available from IBM, with PC DOS and UCSD p-System. It was released six months after DOS, and porting applications from CP/M to either operating system was about equally difficult. Digital Research released a version for the proprietary IBM Displaywriter, and on some non-IBM PC-compatible 16-bit computers like the DEC Rainbow and Zenith Z-100, CP/M-86 could natively run CP/M applications. On the IBM PC, however, at US$240 per copy CP/M-86 sold poorly compared to the $40 PC DOS; one survey found that 96.3% of IBM PCs were ordered with DOS, compared to 3.4% with CP/M-86 or Concurrent CP/M-86. In mid-1982 Lifeboat Associates, perhaps the largest CP/M software vendor, announced its support for DOS over CP/M-86 on the IBM PC.
By early 1983 DRI lowered the price of CP/M-86 to $60. Advertisements called CP/M-86 a "terrific value", with "instant access to the largest collection of applications software in existence ... hundreds of proven, professional software programs for every business and education need"; it also included their Graphics System Extension (GSX), formerly $75. In May 1983 the company announced that it would offer DOS versions of all of its languages and utilities. It stated that "obviously, PC-DOS has made great market penetration on the IBM PC; we have to admit that", but claimed that "the fact that CP/M-86 has not done as well as DRI had hoped has nothing to do with our decision". By early 1984 DRI gave free copies of CP/M-86 to those who purchased two CP/M applications, and advertisements stated that the applications were booters that did not requiring loading CP/M-86 first.
CP/M-86 and MS-DOS had very similar functionality, but were not compatible because the system calls for the same functions and program file formats were different, so two versions of the same software had to be produced and marketed to run under both operating systems. The command interface again had similar functionality but different syntax; where CP/M-86 (and CP/M) copied file
TARGET with the command
PIP TARGET=SOURCE, MS-DOS used
COPY SOURCE TARGET.
Initially MS-DOS and CP/M-86 also ran on computers not necessarily hardware-compatible with the IBM PC such as the Apricot and Sirius, the intention being that software would be independent of hardware by making standardised operating system calls to a version of the operating system custom tailored to the particular hardware. However, writers of software which required fast performance made direct calls to the IBM PC hardware instead of going through the operating system, resulting in PC-specific software which performed better than other MS-DOS and CP/M-86 versions; for example, games would display fast by writing to video memory directly instead of suffering the delay of making a call to the operating system, which would then write to a hardware-dependent memory location. Non-PC-compatible computers were soon replaced by models with hardware which behaved identically to the PC's. A consequence of the universal adoption of detailed PC architecture was that no more than 640 kilobytes of memory were supported; early machines running MS-DOS and CP/M-86 did not suffer from this restriction, and some could make use of nearly one megabyte of RAM.
PC Magazine wrote that CP/M-86 "in several ways seems better fitted to the PC" than DOS; however, for those who did not plan to program in assembly language, because it cost six times more "CP/M seems a less compelling purchase". It stated that CP/M-86 was strong in areas where DOS was weak, and vice versa, and that the level of application support for each operating system would be most important, although CP/M-86's lack of a run-time version for applications was a weakness.
A given version of CP/M-86 has two version numbers. One applies to the whole system and is usually displayed at startup; the other applies to the BDOS kernel. Versions known to exist include:
|CP/M-86 for the IBM Personal Computer Version 1.0||2.2||April 1982||Initial release for the IBM PC.|
|CP/M-86 for the IBM Personal Computer Version 1.1||2.2||March 1983||Hard drive support was added.|
|CP/M-86 Plus Version 3.1||3.1||October 1983||Released for the Apricot PC. Based on the multitasking Concurrent CP/M-86 kernel, it could run up to four tasks at once.|
|Personal CP/M-86 Version 1.0||3.1||November 1983||Released for the Siemens PG685.|
|Personal CP/M-86 Version 3.1||3.3||January 1985||A version for the Apricot F-Series computers. This version gained the ability to use MS-DOS formatted disks.|
|Personal CP/M-86 Version 2.0||4.1||1986 or later||Released for the Siemens PC16-20. This is the same BDOS used in DOS Plus.|
|Personal CP/M-86 Version 2.11||4.1||1986 or later||Released for the Siemens PG685.|
All known Personal CP/M-86 versions contain references to CP/M-86 Plus, suggesting that they are derived from the CP/M-86 Plus codebase.
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