[klodolph]

There are three metrics getting thrown around:

* Performance per dollar operating cost (performance per watt is closest to this)

* Performance per dollar capital expenditure (important for desktop systems, where operating costs are low)

* Performance per dollar TCO (sum of the above two)

The third one is the important one.

[jeffdavis]

Good summary, but after reading this thread I'm still confused.

Why ARM?

How does the ISA impact the aforementioned criteria?

Why would a phones demand a different ISA?

[Tuna-Fish]

The original choice of ARM for mobile and x86 for desktop is basically a historical accident.

The differences between modern ARM cpus and modern x86 have less to do with the ISA itself and more to do with the way ARM cpus have been designed to be low-power for decades and have worked their way up the performance scale, while x86 has been designed for performance and has only lately been emphasizing low power. These lead to different design points.

[userbinator]

Good paper about this here: http://research.cs.wisc.edu/vertical/papers/2013/hpca13-isa-...

[gaius]

Because everything today is about the heat generated by computation. In a phone, it wastes the battery and is unpleasant for the user. In the datacentre, heat determines how much computation you can do in the volume of space you have, and how much you have to spend on cooling systems (the running of which is expensive too). So datacentre operators that already have a building are facing a choice: get a new building, or make better use of the one they have.

ARM cores are typically slower in absolute terms than Intel cores, but at a given level of power, you can run more of them.