> They're designed to run instructions
ARM can do a small subset of what x86_64 can do. Let's say for a minute ARM doesn't have a built in H.264 decoder (they both do, but that's the one feature popped into my head).
The x86_64 chip will be able to do execute the decoding of a H.264 file that faster and more efficiently than the ARM chip because the x86_64 has purpose designed instruction to do this or make the job easier.
Another Example. x86_64 can multiply and divide while ARM can't. Both chips can do the same work, but x86_64 can multiply 20*4 in one instruction while the ARM chip has to do 20 + 20 + 20 + 20, with each one being an addition instruction. ARM might be able to add faster than x86_64, but x86_64 will still be able to multiply faster. That's extremely simple, but when you get into more complex operations ARM has to spend more time doing what x86_64 can do.
> An i7 isn't going to run iOS more slowly than whatever Apple calls their latest ARM SoC.
an i7 will run iOS slowly because iOS is build specifically for ARM. Just like how PS3 emulators take a lot of effort to run on x86_64 chips, there is an emulation overhead.
> It _is_ going to blow its lid without a big ole heatsink brick on there and a fan too, which is why smartphones use ARM cores designed for efficiency.
Yeah, because it's designed to run at a higher thermal envelope. To get ARM anywhere near the Floating Point performance of an i7 you will need to increase the power and throw some active cooling on it.
> P.S. if anything, ARM is the "general purpose vehicle" in your analogy.
I don't think so, as seen above and below.
> x64 is all about high throughput and high power on a chip you buy and plug in.
Yes, because OSs have been designed to use as much as the chip can offer it. But I can get a 5 watt Intel CPU will will run circles around a 5 watt ARM chip.
> ARM is the one where you can get an architecture license and customize the shit out of it.
Yes, so you design it to fit your specific functions. Apple's CPUs only implement what the the engineers need it to, so they can save die space by not implementing unused instructions. You are proving my example here. ARM is the Customized Purpose built USPS Truck, while x86_64 is a general purpose F150. The USPS build their truck to fit their needs just as ARM Chips are built to meet the needs of the consumers.