Castreen
Said..
All Intel processors use the ISA instruction set developed back in the early 80s. First it was an 8-bit instruction set. Then there was the 16-bit. Next came the 32-bit instruction set, and the processors since the 80386 use it. Each processor model designates with the 80x 86 notations. Each model increase in features and sometimes performance. Now the x86 computer industry is advancing towards the 64-bit instruction set.
Pentium III is an 80686. Pentium 4 is an 80786.
For Pentium 4, you have to find programs that are compiled for the Pentium 4 or else the performance will be low.
8086 = 8-bit, 80186 = 8-bit, 80286 = 16-bit, 80386 = 32-bit, 80486 = 32-bit, 80586 = 32-bit = Pentium, Pentium MMX, K5, K6, K6-II, K6-III
80686 = 32-bit = Pentium Pro, Pentium II, Pentium III, Athlon, Athlon XP, Opteron*, Athlon FX-51*, Athlon FX-53*, Athlon 64*
80786 = 32-bit = Pentium 4
* = 32-bit/64-bit
If you have compiled a program for 686 architectures, only the processors equal to it or above it can execute it. If you have compiled a program with MMX/SSE/3DNOW instructions, processors that have it will be optimized and processors that do not have those instructions will not be optimized.