A clock-doubled 486 CPU. The internal speed was doubled without changing the chip's external connections. For example, the 486DX2/66 had an internal speed of 66 MHz, while its external bus from the CPU to RAM ran at 33 MHz. See
Speed Doubler and
iCOMP.
DX2 CPU Internal External
486DX2/66 66 MHz 33 MHz
486DX2/50 50 MHz 25 MHz
486DX/50 50 MHz 50 MHz
DX4 CPU Internal External
486DX4/75 75 MHz 25 MHz
486DX4/100 100 MHz 33 MHz