I have a question about embedded ARM processors and how they actually compare to the x86 architecture.
Is there any comparison of mobile arm chips to Intel's x86 in terms of performance per watt? Like if I have say an ARM cortex A8, could that be compared to a Pentium III? at the same clock how would a P 3 stack against an A8 or an A7?

What about newer cores?
Is a Cortex A58 more or less powerful than a Core 2 Duo?

 

ARM processors are based on RISC (actually, they ARE RISC) architecture and focus on having simple instructions with fast execution and low power operation. This is exactly why you find them in mobile devices (that and because they are very cheap). x86 is a CISC architecture which focuses on having many instructions which are complex so as to make programming easier.

Performance per watt it's hard to measure because what would you consider performance? MIPS alone or the time taken to perform a complex operation. For example, if you wanted to do a large memory transfer from one place to another you could achieve this with a single instruction in x86 but you would need a big chunk of code to do the same in RISC. In that respect, the x86 will always win.

But what about power consumption? And die size? For an x86 chip they are usually very power hungry (100W easily) whereas ARM chips on the whole can get away with not even needing a heat sink. So as you use a tablet to watch youtube that tablet is considerably better (by an order of magnitude) than the x86 streaming a youtube video.

At the end of the day all that matters is the application and what it demands. You cant go comparing ARM and x86 because they are just too different from each other. A good comparison would be "whats the difference between a phenom i x 4 and a core 2 duo".

ARM should be compared to micros like PICs, AVRs and others

 

could that be compared to a Pentium III?

depending on what you are trying to compare.