At the time it was assumed that other DOS licensees would be building their own architecture. There were several kinds of "DOS-compatible" computers, most notab

At the time it was assumed that other DOS licensees would be building their own architecture. There were several kinds of "DOS-compatible" computers, most notably the PC-98[0], which had MS-DOS and Windows ports but no IBM compatibility whatsoever. Several other companies would then try to clone the IBM PC; they all got shut down for copying the BIOS code. The PC clone market only kicked off once Compaq was able to write a legally distinct BIOS. Another part of the reason why Microsoft was able to sell IBM a nonexclusive license boils down to their existing business relationship. Microsoft was just their BASIC vendor and they sold BASIC to everyone. IBM wanted CP/M-86, but Digital Research was taking too long to ship it. Seattle Computer Products[1] was also making 8086-based computers but had no OS for them, so they wrote their own - QDOS. Microsoft was willing to buy QDOS and port it to the PC for IBM, which fixed IBM's biggest problem with the PC, so why wouldn't they take the license? In order for IBM to object to taking a nonexclusive DOS license, they'd have to both realize that the clone market was going to be huge, and that the IBM PC BIOS would not be enough protection against clones. Both of which were not at all certain when the IBM PC was under development. Remember, the whole point of the IBM PC was to put together something quickly because they were playing catch-up to Apple and Commodore, not to build a computing empire like IBM's enterprise business. [0] The machine Touhou started on. Also the machine so difficult to do animated graphics on that most developers made pornographic visual novels instead. Like to the point that the Japanese market would just assume PC games were porn. [1] A subsidiary of the SCP Foundation