DOS is a family of disk operating systems primarily consisting of MS-DOS and a rebranded version under the name IBM PC DOS which were introduced in 1981, as well as some later compatible systems from other manufacturers: DR-DOS (1988), ROM-DOS (1989), PTS-DOS (1993), and FreeDOS (1998). MS-DOS dominated the x86-based IBM PC compatible market between 1981 and 1995. 

Dozens of other operating systems also use the acronym "DOS", including the mainframe DOS/360 from 1966. Others are Apple DOS, Apple ProDOS, Atari DOS, Commodore DOS, TRSDOS, and AmigaDOS. 

IBM PC DOS (and the separately sold MS-DOS) and its predecessor, 86-DOS, resembled Digital Research's CP/M—the dominant disk operating system for 8-bit Intel 8080 and Zilog Z80 based microcomputers. DOS instead ran on Intel 8086 16-bit processors. Starting with MS-DOS 1.28 and PC DOS 2.0 the operating system incorporated various features inspired by Xenix, Microsoft's variant of Unix. 

When IBM introduced the IBM PC, built with the Intel 8088 microprocessor, they needed an operating system. Seeking an 8088-compatible build of CP/M, IBM initially approached Microsoft CEO Bill Gates (possibly believing that Microsoft owned CP/M due to the Microsoft Z-80 SoftCard, which allowed CP/M to run on an Apple II). IBM was sent to Digital Research, and a meeting was set up. However, the initial negotiations for the use of CP/M broke down; Digital Research wished to sell CP/M on a royalty basis, while IBM sought a single license, and to change the name to "PC DOS". Digital Research founder Gary Kildall refused, and IBM withdrew.
what oprocessor did IBM use int heir PC?
who did IBM initially approach?
why did they talkk to him?
what card might have given that impression?
what did that do?
what does DOS stand for?
name 2 main versions?
when were they introduced?
which market did MD-DOS dominate?
what years?
what year was FreeDOS launched?
what launched in 1988
which  mainframe OS uses the acronym?
how many Apple versions were there?
name one
16-bit
16-bit
Bill Gates
 Bill Gates
possibly believing that Microsoft owned CP/M
possibly believing that Microsoft owned CP/M
the Microsoft Z-80 SoftCard
the Microsoft Z-80 SoftCard
allowed CP/M to run on an Apple II
allowed CP/M to run on an Apple II
disk operating systems
 disk operating systems
MS-DOS and  IBM PC DOS
MS-DOS and a rebranded version under the name IBM PC DOS 
in 1981
 in 1981
the x86-based IBM PC compatible market
the x86-based IBM PC compatible market
1981 and 1995
1981 and 1995
1998
1998
DR-DOS
DR-DOS
DOS/360
DOS/360 
Two
Apple DOS, Apple ProDOS
Apple ProDOS
Apple ProDOS