Early Digital Research CP/M Source Code

By the time personal computers based on microprocessors began to emerge in the mid-1970s, programmers had been writing operating systems for about twenty years. Big mainframe computers had operating systems that were huge and complicated, created from hundreds of thousands of lines of code. But other operating systems, designed to fit in the small memory of minicomputers, were tiny. That was the kind that the PCs could use. Computer Scientist Gary Kildall created just such an operating system in 1974 for a small computer called the "Intellec-8" that Intel had designed to showcase their new microprocessors. It was called "CP/M".