There have been a number of Pentium processor lines STARTING with the base Pentium in 1993.The of the recent Pentium entries are Pentium III and Pentium 4.

a) In a Pentium III processor, the BUS speed is generally 133 MHz (although there were a few with 100 MHz). The lowest bus speed on a Pentium IV is 400 MHz, and there are versions with much higher speeds (TOPPING at 1066 MHz for the "extreme edition").
B) The Pentium 4s are smaller than the Pentium IIIs
c) Pentium III processors had (for the most part) about 512 KB of cache. Pentium 4 processors, on the other hand, start at 512 KB. 

There have been a number of Pentium processor lines starting with the base Pentium in 1993.The of the recent Pentium entries are Pentium III and Pentium 4.

a) In a Pentium III processor, the bus speed is generally 133 MHz (although there were a few with 100 MHz). The lowest bus speed on a Pentium IV is 400 MHz, and there are versions with much higher speeds (topping at 1066 MHz for the "extreme edition").
b) The Pentium 4s are smaller than the Pentium IIIs
c) Pentium III processors had (for the most part) about 512 KB of cache. Pentium 4 processors, on the other hand, start at 512 KB.