[3] SCP wanted to offer the 8086-version of CP/M that Digital Research had initially announced for November 1979, but it was delayed and its release date was uncertain.

[citation needed] Microsoft purchased a non-exclusive license for 86-DOS from Seattle Computer Products[9] in December 1980 for US$25,000.

[citation needed] In May 1981, it hired Tim Paterson to port the system to the IBM PC,[3] which used the slower and less expensive Intel 8088 processor and had its own specific family of peripherals.

IBM watched the developments daily,[3] submitting over 300 change requests before it accepted the product and wrote the user manual for it.

[3][10][11] It met IBM's main criteria: it looked like CP/M,[2] and it was easy to adapt existing 8-bit CP/M programs to run under it, notably thanks to the TRANS command which would translate source files from 8080 to 8086 machine instructions.

The deal was spectacularly successful, and SCP later claimed in court that Microsoft had concealed its relationship with IBM in order to purchase the operating system cheaply.

Nonetheless, Kildall confronted IBM and persuaded them to offer CP/M-86 with the PC in exchange for a release of liability.

Perhaps the most sensational claim came from Jerry Pournelle, who said that Kildall personally demonstrated to him that DOS contained CP/M code by entering a command in DOS that displayed Kildall's name,[12][nb 1] but Pournelle never revealed the command and nobody has come forward to corroborate his story.

[16] The court ruled in summary judgment that no defamation had occurred, as the book's claims were opinions based on research or were not provably false.

The Western Digital FD1771-based Cromemco and Tarbell boards supported one-sided, single-density soft-sectored drives.

Under 86-DOS, the reserved sectors area is significantly larger (whole tracks), and therefore the prototypical FAT ID 0xFE (and 0xFF) is located elsewhere on disk, making it impossible for MS-DOS to retrieve it, and even if it would, the hard-coded disk profile associated with it would not take this larger reserved sectors region under 86-DOS into account.

[nb 2] Disk formats supported by one of the last versions developed by Tim Paterson at Microsoft, MS-DOS 1.25 [21][26][27][28] (March 1982) for the SCP Gazelle computer with SCP controller or Cromemco 16FDC controller (by default, this version only supported the MS-DOS-compatible variants of the 8.0 in formats with a single reserved sector but it could be built to provide two extra drive letters to read and write floppies in the previous SCP 86-DOS 8.0 in disk formats since 0.42 as well): In 1984 Seattle Computer Products released an OEM version of MS-DOS 2.0 for the SCP S-100 computer with SCP-500 Disk Master Floppy controller.