Killer Doom CPU
This was when having a cpu multiplier was a new idea, before this everything ran on the same clock. With the DX50 this started to cause problems with everything at 50mhz.
The dx2/66 was 66 mhz with everything else at 33 mhz.
dx4/100 was the cpu tripled to 99mhz with a base clock of 33mhz.
No one wanted to name a cpu a DX3 so they just called it a DX4 even though it was tripled and not quadrupled.
In some benchmarks and in Doom the dx4/100 was very close to the new (and expensive) Pentium 66 and Pentium 60. Intel started holding back production of the dx4/100 to force people to go with the Pentium.
Cyrix along with AMD were lower cost alternatives to intel. I remember at Fry’s a dx2/50 CPU and MB cost about the same as an Intel 386 CPU+MB.
These were also the days when you could install 256k of level2 cache on your MB for another speed boost.
Hope this helps