During the sixties when the biggest computer company was IBM or "Big Blue" as it was known in its day, everything was mainframe, the only people that had computers were large companies.
Enter Apple-Mac with the first PC or personal computer. IBM had thought that all computers would be main frames, they were caught well and truly on the hop.
With absolutely nothing that came close to the new Apple, IBM were in a frenzy to catch up. The quickest way was to just take off the shelf components from third parties, and put them together, enter Intel, with no time for IBM to research and develop; Intels chips were thrown together to make a PC. This left IBM with only having to work on one chip, the B.I.O.S. (Basic Input Output System), this would join with the operating system which was coming from another third party, to their computer.
During this time IBM had a software problem which had to be fixed before Monday, as this was the weekend they went round to the house of their software contractor to get it fixed. They got there just in time but the contractor was just about to go for a round of golf and told them to go and come back on Monday. The IBM engineers in a flap, still had this problem to get fixed, so they phoned the new up and coming star of the computer world Bill Gates.
The old software contractor was out, Bill Gates was in, who later formed Microsoft. A marriage made in heaven, or so it seemed. The two companies worked together until a new OS was required. IBM had their eyes on their own OS2 but Bill Gates saw the light mainly coming from other platforms which already had graphical interfaces. They were the way ahead, so he went ahead and made his Windows.
This split could have been the end of Micorsoft, but IBM's Achilles heel suddenly showed. The IBM pc which wasn't really designed to do anything, except, just be there to compete with Apple Mac. Built with only off the shelf components from another companies and only one custom chip, made the IBM PC the easiest computer platform in the world to copy or clone.
With a multitude of companies now ready to jump on the IBM PC clone band-wagon, and Microsoft quite happy to sell them his Windows Operating System, the future was set.
Bill Gates had found an avenue for his Windows OS, and the clone manufacturers had found a computer platform to make, with no or little research and development costs of their own. This allowed computers to be made cheaper than before, and so the PC as we know it today quickly rose up to become the computer 90% of the computer owning world useses. All this because IBM clone computers could be made cheaper than Apple-Macs, and because the clone manufacturers were also competing with themselves.