The availability of mini-ITX and more recently thin mini-ITX motherboards have allowed for some very small PCs to be built. There are a few limiting factors, though. Such tiny cases won't fit a graphics card inside and cooling is compromised meaning your choice of processor is also limited.
FanlessTech brought our attention to SilentPCReview Forum poster amishware, who decided to disregard conventional thinking and managed to fit the 69mm-tall Arctic Alpine 11 passive CPU cooler into a 41mm-tall acrylic case. You can immediately see how that would be a problem as the cooler is deeper than the case, but with a little modification, it works.
Yes, this setup may look a little bit unusual, but it does allow for a higher performing processor to be used without a fan spinning. In this case the cooler is sitting on top of a 2013 2.7GHz Intel Celeron G1620, which has a TDP of 55 watts (a little higher than Arctic recommends for the Alpine 11). That could easily be swapped out for a 4GHz Core i3-7300 chip (51 watts TDP) while retaining the same passive cooling setup and a big jump in performance. Of course, you'd need to upgrade the motherboard and RAM, too.
- Akasa Made a Fanless Case for Intel's Skull Canyon NUC Akasa Made a Fanless Case for Intel's Skull Canyon NUC
The full spec of this unconventional and still tiny PC includes a Gigabyte GA-B75TN motherboard, Intel Celeron G1620 processor, 8GB 1,600MHz Kingston DDR3 RAM (2 x 4GB sticks), an Arctic Alpine 11 passive CPU cooler, and a 120GB Samsung SSD 750 EVO SSD.
If nothing else, it proves that you can retain passive cooling even if space is very limited. The compromise made is the final look of the PC, and I'm sure many PC builders would have no problem with a big block of metal hanging out the side of their case if it meant silent running was achieved.