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It's worth mentioning Zen2/Zen3 AMD CPUs can be run in Linux* with kernel parameter: amd_pstate=active

This allows for the CPU to run in an extreme low-power state and scale up if needed.

• Kernel 6.5+ required

In general efficiency is a difficult metric for CPUs because there are many different definitions and factors that are involved.

If you want a low electricity bill:
There are boards with an intel N100 (TDP 6W).

There are some ARM chips that go down to microamps in low power mode and draw only 1 Watt at full power but might drive you nuts trying to run Linux on them.

Another poster sent you an exhaustive list, but to answer your question a bit, AMD has been dominating in the performance/watt category for a while now, I'd consider a Ryzen processor. Anything made in the last few years will be more than robust for what you're describing. Hell, if you're willing to wait for delivery I bet a Raspberry Pi 5 could suffice

I'm a big fan of SuperMicro's Xeon D- series 1U short servers. Not really consumer grade, but not overly expensive either (about $1k on ebay for everything but the disk), and power consumption was not much higher than Atoms at the time I bought them.

https://ark.intel.com/content/www/us/en/ark/products/series/87041/intel-xeon-d-processor.html

I have a D-1541, 8 core (16 thread), 2100MHz @ 45W TDP, and two D-1518s, 4 core (8 thread), 2200MHz @ 35W TDP. They'll both run proxmox with a handful of containers, and another selling point was 10GbE, which is great if you're looking to upgrade your LAN.

If you're not doing much computing, then the idle power consumption is much more important than the tdp, in which case the motherboard and other hardware are more important than the CPU. For your use case, something like a tinyminimicro 1L PC or a Celeron mini PC would be good. I've personally played around with

• a dell optiples 3050 micro with an i5-7500t that idles about 6 watts
• an AliExpress n5105 mini PC that idles about 8 watts
• an AliExpress n100 3inch mini PC that idles about 5 watts
• an Asus Chromebox 3 with an i7-8550u that idles about 4 watts Any of these have plenty of juice to run some docker containers and a media server assuming you don't need to transcode multiple 4k streams simultaneously. I'm currently using the Chromebox as my proxmox server with 3-4 vms and maybe 20 docker containers/lxcs and it uses about 8-9 watts on average.

is 35W to much ?

N100 is a good low power CPU (I own one) but beware that they only have 9 PCIe lanes. Every peripheral and motherboard slot needs at least one lane and many (like NVME slots) often have more. For example, NVME normally uses 4 lanes and each NIC needs one.

So, do the math, 2 standard NVME slots and a NIC use all your lanes so there would be none for the PCIe slots.

The Asrock N100m tries to deal with this but limiting the number of lanes per device but it does so, potentially, at the expense of performance. It assigns 2 lanes to the NVME slot and it's 16 lane PCIe slot only wires 2 of those lanes. Shit should still work, but it may not be at its fullest performance.

Anyhow, beware that striving for lowest idle power may have other hidden costs if you also want flexible and high speed I/O.

As others have mentioned, TDP is a poor indicator of idle wattage.

In general, two things that are better predictors of idle wattage: newer chips and core count. Makes sense, right? Newer stuff is more efficient which is how they either cut power or jam more cores into a chip.

As many have mentioned the N100, N200, N305 have been popular, and ASRock has some mobos with that combo, but they will be lacking the connectivity you're looking for.

In terms of a CPU I would look at either newer Celeron or i3 variants (there is a reason the lower end enterprise grade servers run off them). Combine this with "industrial" motherboards ("IMB" from ASRock and Gigabyte, also "Jetway" products, etc.) which have plenty of I/O, compact form factor, and very little "wasted" on performance gaming stuff and RGB fluff. Some of those industrial motherboards also have embedded CPU options from either laptop or embedded series which would also idle super low but still be plenty for your needs while retaining Intel Quicksync for transcoding.

i5, i7 and i9 are probably too much for your workload and those extra cores will sit and eat power and do nothing for you. Same with most of the Xeons plus you probably lose QuickSync outside of a select few variants.

https://pcpartpicker.com/products/cpu/#sort=tdp&page=1

The Intel NUC's with 13th gen CPU idle at less than 10w. They have a i5-1340p CPU.