Intel 486DX4 Microprocessor

Despite the name, the Intel 486DX4 microprocessor does not run internally at four times the memory bus speed, but rather at triple the external clock speed. Since Intel reserved the "DX3" designation for a 2.5 times clock multiplier that never reached the marketplace, they had to create the newer moniker, the "DX4". Although Intel never produced one, clone makers such as Advanced Micro Devices (AMD) and Cyrix sold 5x86 central processing units (CPUs) that were actual clock quadruplers.