Here is my question:

How is it that processors based on the ARM architecture, designed for mobile devices are so much more efficient than mainframe chips?

Comparing two instruction set architectures; ARM and X86, how is it that ARM chips can run on so much less power? How is it possible for them to cram so much logic onto a single chip, and still retain the power efficiently?
Like, an ARM system on chip is an entire computer. The CPU, GPU, DSP, RF baseband and Input/ Output all on a piece of silicon. Even though each of these cores are low power, low circuit content, it still has the same amount of transistors as a desktop processor I.E Intel X86?
Where so an so million transistors in an Intel chip would be only the CPU and it's buses and memory, for an ARM chip this is the entire computer?
Can you help me understand the differences?

 

https://research.cs.wisc.edu/vertical/papers/2013/isa-power-struggles-tr.pdf

There is a large gap in pure CPU power from the top line x86 vs ARM. The simple physics are that if ARM reaches the pure general performance computing level of the X86 the Energy consumption of the chips will be similar with x86 currently being more efficient.
http://www.extremetech.com/extreme/...86-or-mips-intrinsically-more-power-efficient