[nb 1] 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.

The IBM PC was announced on 12 August 1981, and the first machines began shipping in October the same year, ahead of schedule.

BYTE speculated that Microsoft reserving multitasking for Xenix "appears to leave a big opening" for Concurrent CP/M-86.

[13] BYTE warned that IBM, Microsoft, and Lifeboat's support for DOS "poses a serious threat to" CP/M-86,[5] and Jerry Pournelle stated in the magazine that "it is clear that Digital Research made some terrible mistakes in the marketing".

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 accessed the IBM PC hardware directly 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.

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.

[26][25] Caldera permitted the 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" since 1997.

[27][28][29] After Olmstead's death on 12 September 2001,[30] the free distribution license was refreshed and expanded by Lineo, who had meanwhile become the owner of those Digital Research assets, on 19 October 2001.