DX2 - technical definition

A 486 with a clock-doubled CPU. Clock doubling doubled the internal speed of the CPU without requiring any changes in 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. The 486DX2/50 had an internal speed of 50 MHz and 25 MHz externally. Intel called the DX2 a "Speed Doubler" chip.

     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