I have a _very old_ PN40 from Asus -- this is a full PC with an intel Celeron, a SATA SSD and about 8GB of RAM that idles at 1.7W (serving websites via GB Ethernet) as measured _at the wall_. This is just standard PC Linux distro with zero customization (other than `powertop --auto-tune`).
For comparison, the latest RPI4B without the SSD and with 1/8 RAM idles at 3.5ishW on the wall. Even the older RPI3 I could never get below 2W, and that is without any peripherals (no display, no Wifi, no eth, min USB) and significant tuning.
On the other hand the PN40 + components cost significantly more (probably close to 10x), and the CPU performance itself is not that good these days.
https://raspi.tv/2019/how-much-power-does-the-pi4b-use-power...
- The Odroid H2+ x86 board claims about ~4W idle power: https://www.hardkernel.com/shop/odroid-h2plus
- This measurement of idle power on the Raspberry Pi 4 says it uses ~3.4W: https://www.tomshardware.com/reviews/raspberry-pi-4
in the past as a relatively cheap x86 CPU. ($9.62 per unit)
However, it's a 400MHz 486 with some backports (1st generation Pentium, no MMX even) and broken LOCK prefix so that software specifically needed to be recompiled for it.
And at 2.2 W too, it never ended up succeeding anywhere, with no successor.
The right era pentium had the same LOCK prefix issue (we used to call it the F00F bug)
Edit: Thanks for link; I must have anchored on the instruction set and ignored that it was using the 486 pipeline.
"The new x86 CPU uses an old-school 486 scalar pipeline and the original Pentium instruction set with some modern enhancements"