http://www.techspot.com/article/874-history-of-the-personal-computer/
The personal computing business as we know it owes itself to an environment of enthusiasts, entrepreneurs and happenstance. Before PCs, the mainframe and minicomputer business model was formed around a single company providing an entire ecosystem; from building the hardware, installation, maintenance, writing the software, and training operators.This approach would serve its purpose in a world that seemingly required few computers. It made the systems hugely expensive yet highly lucrative for the companies involved since the initial cost and service contract ensured a steady stream of revenue. The "big iron" companies weren't the initial driving force in personal computing because of cost, lack of off-the-shelf software, perceived lack of need for individuals to own computers, and the generous profit margins afforded from mainframe and minicomputer contracts.
It was in this atmosphere that personal computing began with hobbyists looking for creative outlets not offered by their day jobs involving the monolithic systems. The invention of the microprocessor, DRAM, and EPROM integrated circuits would spark the widespread use of the BASIC high-level language variants, which would lead to the introduction of the GUI and bring computing to the mainstream. The resulting standardization and commoditization of hardware would finally make computing relatively affordable for the individual.
Over the next few weeks we'll be taking an extensive look at the history of the microprocessor and the personal computer, from the invention of the transistor to modern day chips powering a multitude of connected devices.
Part 1: (1947 - 1974) Foundations: Leading up to Intel's 4004, the first commercial microprocessor