PC BIOS
From Dr David Bradley (the engineer behind the IBM BIOS):
Stay Forever: Did you expect DOS-based clone machines to be available so soon – or weren’t you expecting them at all, since your BIOS should act as a "copy protection" mechanism?
Dr. Dave: Poor planning on our part. Based on the S100 experience we should have expected clones very quickly. But that would have required us to assume that the PC would be a world changing product and we were just hoping for a successful one. So we (or at least me) weren’t expecting them at all.
The BIOS as a protection mechanism was an after the fact method. And easy to work around, as Compaq and Phoenix and others quickly showed. So we could get the low hanging fruit and force the cloners to do a little bit of work.
(https://www.stayforever.de/ibm-pc-a-conversation-with-dr-david-bradley/)
Some companies (Compaq, for one) wrote their own BIOSes, but few matched IBM's. The computers suffered compatibility problems and the compatible market remained small. But in 1984, says Alan Painter, a Phoenix sales representative, "Phoenix provided the first commercially available PC-XT BIOS." Companies such as AMI followed suit, Painter says, "and that's when the PC-compatible market was created."