[adrian_b]

There have been tons of proprietary CPU architectures with the same power efficiency as Arm. Only the x86 architecture is an outlier that requires an unusually complicated instruction decoder, which may degrade a little the energy efficiency.

Arm has eliminated most of the competing CPU architectures not by providing better power or energy efficiency, but by its business model of being licensable to anyone.

The ARM ISA was somewhat better than MIPS and SPARC, both of which have been handicapped by including some experimental features that have been later proved to be bad ideas. However there have been many other RISC ISAs more or less equivalent with ARM. Only the business model has extracted ARM from the crowd, not its technical advantages.

[klelatti]

You're conflating the characteristics of the ISA with the value proposition offered by the designs using it. Not the same at all.

Other historical architectures typically targeted higher performance.

Arm specifically went after low-power applications, which continues today when we see the priorities in the design of Arm and x86 cores, for example.

[adrian_b]

Arm "specifically went after low-power applications" only in comparison with x86 or in comparison with a few other architectures restricted to workstations and servers, like DEC Alpha or Intel Itanium.

Before 2000, there were at least a dozen CPU architectures that went for the same low-power applications as Arm. There were a lot of microcontroller or processor vendors and each one of them had at least one proprietary ISA, if not 2 or 3 or even more different proprietary ISAs.

More than 20 years ago, I have redesigned various kinds of communication equipment, in order to replace many other kinds of CPUs, for example Motorola MC683xx or ColdFire or IBM PowerPC CPUs, with Arm CPUs.

In none of those cases the Arm CPUs had a lower power consumption or any other technical advantage. In fact in all cases the Arm CPUs were technically inferior to the CPUs replaced by them, which has required the implementation of various hardware and software workarounds.

There was only one reason why the Arm CPUs had been selected to replace their predecessors with different architectures, and that was the lower price. Their lower price was in great part due to the fact that there already were many competing vendors of Arm CPUs, so if you did not like one of them it was easy to replace it with another vendor.

[klelatti]

I get it that you don’t like Arm but that doesn’t change the fact that low power was and is central to their value proposition - and this latter fact doesn’t preclude other firms having low power offerings.

[soulbadguy]

It's been said many time and the correlation between ISA and power efficiency have been debunked many time. ARM is power efficient because most ARM implementation are power efficient. Right now x86 AMD strix are about on par with qualcom x elites

[klelatti]

Agreed. That power efficiency is still a central part of the Arm value proposition though. Others are competing with real designs on this with Arm in laptops but not in - for example - smartphones.