First off, let's talk about the very few similarities between the two CPU architectures :
They both are x86 CPUs, that's how similar they can get.
And now the differences :
They're not pin-compatible, meaning that they each require a different socket, chipset, motherboard and cooling system.
Intel's Pentium4 and Celeron CPUs currently use a 478 PGA socket that replaced the short lived 423 pins socket, P4s will eventually migrate to an LGA 775 socket that is due this summer.
AMD's Athlon, Athlon XP and Duron CPUs use a 462 PGA socket, the first Athlons required a slot instead of a socket to accomodate the slow off-die L2 cache. Athlon64 and AthlonFX respectively use 754 and 940 PGA sockets, AMD just introduced their 939 PGA platform which will replace socket 754, socket 940 will therefore be reserved for AMD Opteron CPUs which are aimed at the workstation and server market.
Intel's Pentium4 was originally designed around Rambus RDRAM and a quad-pumped bus, now, P4 motherboard feature single or dual-channel DDR-SDRAM chipsets.
AMD Athlon, Athlon XP and Duron CPUs are based on the EV6 dual-pumped bus, single-channel DDR-SDRAM is enough to fullfill their bandwidth requirement but dual-channel chipsets and motherboard are the norm.
PGA 754 Athlon64 feature an on-die single-channel memory controller and are picky about memory modules, PGA 939/940 Athlon64 and FX use an improved dual-channel on-die memory controller. Socket 940 AthlonFX and Opteron processors require expensive and rare Registered DDR-SDRAM memory, CPUs based on sockets 754 and 939 both use cheaper and easely available DDR-SDRAM.
Intel and AMD both use similar yet different instruction sets on top of their common x86 code, their CPUs don't handle logic operations and cached data in the same way.
Intel chose to market their CPUs based on the frequency at which they operate, AMD uses a model based rating system, PGA775 P4s will most likely be marketed by model # as well.
Both architectures tend to equally outshine the other depending on the task being performed, even a combination of unbiased benchmarks can't tell who's the best overall, nobody agrees on a benchmarking procedure anyway, it's all about PR IMHO.
I probably forgot to mention a lot of stuff but this post is getting waaaay too long for my taste (I already edited trice for typos and omissions), please refer to <A HREF="
http://users.erols.com/chare/" target="_new">This Page</A> for more information about Intel's and AMD's CPUs.
I hope I answered your question properly, just reply if I did'nt !
Fok Speling Misstake