ARM CPUs carry a typical TDP of <5W or so, give or take. A "fast" ARM CPU typically hits about 2.0GHz and might have four cores or so packed into a die, and each core is highly efficient (especially at idle). Some ARM chips can sort of compete with an old Core Duo depending on the benchmark. But all of them are designed for rather small TDPs compared to say, a desktop x86 CPU (which can consume well over 100W depending on the make and model).
I know of the exponential relationship between switching (clock) speed and power, etc., but:
- Why are there no high-TDP ARM chips?
- If it's because of performance or high-power efficiencies, how would one compare to a modern day Ivy Bridge or Steamroller?
- And ultimately (edit: from a technical perspective, disregarding funds), what is limiting manufacturers from cranking ARM to >90W? Die size? Performance? Architectural limitations?
I hope this is the right subforum for this. I've been wondering this for awhile and finally figured I'd create an account here to ask. I have some EE and a little CompE background so don't hold back (until I start complaining). Thanks in advance!
EDIT: General answers I've compiled so far:
Wording or points subject to change as conversation evolves
- Diminishing performance returns: ARM is not as efficient as x86, and remains most efficient at low power. Reduced power to performance efficiency at higher clockspeeds would overshadow net performance gains.
- Die size to cooling ratio: ARM typically has a tiny die and pumping 100W through 1.5mm^2 or similar is just not feasible--it's a soldering iron.
- Limited Parallelism: Scaling isn't as easy as just slapping a bunch of cores together, you need to feed them properly. Serial workloads suffer greatly.
- Beyond clockspeed: Current ARM arches don't have the same level of branch prediction/caching/etc as the x86 competition.
- Design: A high-TDP ARM CPU would be worth it only if it were designed from the ground up to work as such, similar to what NVIDIA is doing with Project Denver, or more "advanced" cores like the A15.
- Demand/funding: I dislike this answer because it's not what I'm after, but ok. There's little marketing demand and research into high-TDP ARM.
And here are some things that we might still be disputing:
- ISA: ARM isn't designed to do "as much" at the ISA level as x86 is.
- RISC vs CISC: We can bring this up but many argue that line is blurring.
- It might be worth noting ARM's current lack of 64-bit compatibility or similar hardware limitations for theoretical performance or resource limits.