From: user5857@newsgrouper.org.invalid   
      
   David Brown  posted:   
      
   > On 22/09/2025 17:28, Stefan Monnier wrote:   
   > >> But, AFAIK the ARM cores tend to use significantly less power when   
   > >> emulating x86 than a typical Intel or AMD CPU, even if slower.   
   > >   
   > > AFAIK datacenters still use a lot of x86 CPUs, even though most of them   
   > > run software that's just as easily available for ARM.  And many   
   > > datacenters care more about "perf per watt" than raw performance.   
   > >   
   > > So, I think the difference in power consumption does not favor ARM   
   > > nearly as significantly as you think.   
   > >   
   >   
   > Yes, I think that is correct.   
   >   
   > A lot of it, as far as I have read, comes down to the type of   
   > calculation you are doing.  ARM cores can often be a lot more efficient   
   > at general integer work and other common actions, as a result of a   
   > better designed instruction set and register set.  But once you are   
   > using slightly more specific hardware features - vector processing,   
   > floating point, acceleration for cryptography, etc., it's all much the   
   > same.  It takes roughly the same energy to do these things regardless of   
   > the instruction set.  Cache memory takes about the same power, as do PCI   
   > interfaces, memory interfaces, and everything else that takes up power   
   > on a chip.   
   >   
   > So when you have a relatively small device - such as what you need for a   
   > mobile phone - the instruction set and architecture makes a significant   
   > difference and ARM is a lot more power-efficient than x86.  (If you go   
   > smaller - small embedded systems - x86 is totally non-existent because   
   > an x86 microcontroller would be an order of magnitude bigger, more   
   > expensive and power-consuming than an ARM core.)  But when you have big   
   > processors for servers, and are using a significant fraction of the   
   > processor's computing power, the details of the core matter a lot less.   
      
   Big servers have rather equal power in the peripherals {DISKs, SSDs, and   
   NICs} and DRAM {plus power supplies and cooling} than in the cores.   
      
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