If you are reading this, you probably at least know the basics of what a computer is. Electronic computers were created in the early 1940s, though various mechanical and electromechanical predecessors exist. The first personal computers appeared in 1974 or so. In the 21st century, CPUs started being produced at over 1000 MHz, or 1 GHz in clock frequency. It appears that the maximum clock is around 3 or 4 GHz, because faster CPUs would generate an excessive quantity of heat due to the density of the transistor elements within and their individual power requirements, so multi-core processors with wide, high-speed intercommunication busses have been invented to get around this problem.