The 80486DX4 continued the trend started by the 80486DX2 toward faster clock speed processors on slower motherboards. The DX4 uses "clock tripling", where the processor runs at three times the speed of the memory bus (motherboard). Note that despite the name the DX4 does not run at four times the memory bus speed ("DX3" refers to 2.5 times the memory bus, but never became a shipping product for the 486.)
Intel's DX4 runs at two speeds: 75 MHz (for the 25 MHz bus) and 100 MHz (for the 33 MHz), with the 100 being by far the most popular. In order to keep power and heat to a manageable level the voltage of these chips is reduced to 3.3 volts.
The AMD and Cyrix versions are very similar to their DX2 cousins, in that they are 5 volt tolerant, meaning they can handle being put in a 5 volt motherboard; the Intel chip is not 5 volt tolerant and cannot be put into a 5 volt board (well, you can physically put them into the board, but you shouldn't do it! :) ). AMD and Cyrix also make a 120 MHz version that runs on a 40 MHz bus; this is relatively rare. The Intel, AMD and Cyrix versions of the DX4 chip are quite similar. One difference is that the AMD and Cyrix support write-back cache while the Intel does not; however the Intel has its level 1 cache doubled to 16 KB. All three chips support power management.
The 486DX4 was most commonly put into systems as OverDrive processors for older, slower systems. Intel did not originally make the DX4 available as a stand-alone chip, presumably since it shipped after the Pentium had already been introduced. However, they did make the chip available stand-alone later on. New 486DX4-100 systems were often made with the AMD version of the chip. The OverDrive version is generally required for older motherboards that don't support 3.3 volt power.
Like the 80486DX2, the 80486DX4 is technically obsolete, but the 100 MHz version especially has good processing power for routine applications. It is also acceptable for some other uses, but is not found in modern systems.