Motherboards with fanless cpu - kaby lake?

I agree that a completely fanless system is not possible unless one want the kind of performance now found in tablets or tablet PCs

But one single large, slow system fan should be possible and with decent (i.e. >current consoles) performance. The critical PC component that need cooling are:
-PSU: up to 300-400W fanless or semifanless (a backup fan that starts only when the VRM inside gets real hot) designs exist. Not critical.
-CPU: up to 15-20W fanless is easy doable. Above that, one needs large heatsinks and careful consideration when designing the case airflow. Above 45W, are these passive heasinks still practical (HTPC case should be small, maybe low height/width)?
-GPU: fanless video cards built around entry/mid level GPUs exist. Again, airflow inside must be carefully arranged to avoid GPU throttling under load. Semi passive designs (i.e. blower off below a certain threshold) exist also for high end cards.

Noise of a single large fan spun at low rpg should be very low, completely masked if said pc is put inside a cabinet. During gaming, even if the GPU has a fan that starts spinning under load, it would be less noticeable by a user than in a movie and not a big deal imho. Motherboard has arrived early. Depending on how long the Windows installation (and updating) takes, I'll may be able to share some results even tomorrow.

 

Here's an update. The process of installing and updating took longer than on other recent PC... this is something I new already, since I've used a motherboard with an embedded Atom already for a friend's HTPC.

The N3700 CPU is a dual issue, in order CPU with simple branch prediction 12(14?) stages pipeline. From an architectural point of view, there is nothing fancy about it; it's just like a 1993 Pentium with a longer pipeline to work at higher frequencies. It has four cores, paired in groups of two, each sharing a 1MB L2 cache. It has 32KB instruction and 24KB data L1 caches (odd arrangement). Intel has lowered the BCLK bus to 80MHz, to cripple it further. The GPU is a 16 pipelines 7th generation core, similar to those employed in Broadwell CPUs. It has hardware support for the most recent codecs (I think VP9/h265 only for decoding) making it an ideal choice for a low power HTPC or tablet PC. Oddly enough, Intel has kept a dual channel DDR3 interface, working at 667 or 800 MHz. As for the rest, it's x64 compatible, it supports all Intel SIMD extensions but not virtualization. It's a system on a chip capable of driving 4 PCIe 2.0 lanes (500MB/s each), 4 SATA 6Gbps channels as well as a handful of USB 3.0 ports.

While sold as a 1.6GHz CPU, with a BIOS trick it can be made to work at the nominal 'Turbo' frequency of 2.4 GHz with all cores. It has a claimed TDP of 6.5W.

After installing Windows and the updates, I only had time for a quick Cinebench 15 test and half an hour of Witcher 3... I've chosen this title because it has no DRM and can be litterally moved from one PC to the next by copying the directory (this way I also don't have to re-install mods). This is one of the reasons why I haven't bought a title from Steam in the last two years. I'd rather support GoG and developers who don't force me to have to live with DRM. But, I'm digressing....

Cinebench 15 results were a bit... discouraging to say the least: with a score of 40 (single thread) and 145 (four threads) it's far slower than any CPU I've used in the last 10 years or more...

Afterwards, I started Witcher 3 expecting a bloodbath, but -actually- it was not the case. I ran the game with these settings: 1920x1080 resolution, 'High' detail level, hairworks off, framerate capped to 30fps, vsync. These are the same settings I use on my laptop without problems for a smooth gaming experience.

Despite the slow processor and the 1x PCIe interface to the graphic card (an EVGA GTX1060 SC) the framerate never goes below 30 fps in wilderness areas. In the towns, however, the framerate fluctuates between 19 (lowest observed) and 25-26 fps. Lowering the number of characters or the detail doesn't seem to impact performance. I think the culprit here is the 1x PCIe interface; when loading menus (map, inventory, quest log, etc...) there is always a 1-2 seconds freeze possibly a consequence of loading on the graphic card memory some data.

Now let's talk about the temperatures. In the SG10 case The CPU is sitting below a slow turning 18cm fan. Even during load, the highest core temperatures registered by HWInfo are 58°. When idle, the temperature stays below 30°; ambient temperature in the room was 22°. As for the graphic card, the fan started to spin after a while, but it remains barely audible. GPU temperature, once the fan kicks in, stays below 50°: between the framerate cap and the low power CPU, the graphic processor is probably sitting idle most of the time!

I enclose some screencaps from the Witcher with the EVGA overlay statistics. It was a real pleasant surprise to see that the game is playable (with some hiccups). But both the PS4 and the XB1 don't have a much better CPU, so it follows current games must be optimized to run on multithreaded, but low power CPUs.

 

Dual issue specifically means that the processor can decode and issue a maximum of two instructions simultaneously to the following pipeline stages or functional units. Usually it means just that, a simple 'superscalar' processor like the fist Pentium.

It says nothing of the architecture, unfortunately. The P6 Pentium Pro had a decoder capable of issuing up to three instructions (but not always: one of the decoding units couldn't handle all the instructions of the x86 set).

The new Goldmont Atom is said to be a three issue, out of order processor (has Intel dug out of the archives the blueprints of their P6 derived, Pentium M processor?) but so far, the benchmarks I've seen are not very exciting: 20% more performance in best case scenarios.