CP/M

IBM’s scramble to deliver a PC forced a decision point: they needed an OS fast not to lose the market to Apple or Atari.

Gates offered CP/M, but IBM turned him down, so Microsoft created MS-DOS in a week from scratch.

That move cemented software as a standalone layer that could be licensed repeatedly—no ownership of hardware, just access to the operating system.

Fast forward, and Windows became the de facto platform with Office riding alongside, creating an ecosystem where almost every application ran on Microsoft's stack.