difference in .config options

i am puzzled by the following....:

what is the difference between custom compiling a kernel with the
processor option set for Pentium 4 (p4) and opposed to 686?

 

pentium 4 will enable the options that the cpu has possible to it that say a generic 686 won't have. If you do a cat /proc/cpuinfo. You'll see all the options that the cpu supports...a generic 686 I don't believe has sse2 sse mmx support as default.

 

kewl....thank you so much..

.so in reality....a p4 kernel can use software compiled specifically for p4 and this same software may or may not run on a 606 kernel?