I kind of miss add-in processor cards to allow a computer to run software from another architecture. Those devices were basically a whole computer on a card or add-on that would use the host computer for I/O with some level of integration. Stuff like the Apple IIe card for the Macintosh LC, or the MacCharlie sidecar for the original Macintosh that allowed it to run PC programs.

I bet there are modern PCI cards out there that can add a hard-to-emulate processor to a consumer/prosumer-grade system, but I'm not sure what to search for.

Honestly that's pretty close to what a usb c dock is.

Well if we're going that far, why not just connect your phone to your PC and adb shell into it?

For the Intel chips up to and including the Pentium 4 licensing a chipset would not be an issue. VIA made chipsets back when those products were new. I think there was a lawsuit about it, but VIA prevailed. You could license the chipset from them, then use it with an authentic Intel CPU.

https://en.wikipedia.org/wiki/List_of_VIA_chipsets#:~:text=V....

But to your original point: CPUs don't really fail unless abused is my understanding. The bad ones are filtered out at the factory before they ever get to consumers.

That might even be ideal insofar as the chipset is driver compatible with equivalent from the time. Via wasn't anything special but they were super common and thus decently supported IIRC.

Except Pentium 4

There is a precedent for that with the reproduction Amiga motherboards that came out a couple of years ago. Those were actually just pcbs but something more accessible would be cool.

Chinese companies are making new boards for >=Nehalem Xeons using recycled server chipsets, mostly because they're still OK for gaming on a budget.

If there was a demand they could probably do the same for older models if they can harvest enough chipsets. There were quite a few 430HX's on embedded modules that could be recycled...

This is an avenue I’d like to see more pursuit of, and not just for x86 machines — new PowerPC mac motherboards that can be fitted into standard ATX PC cases and can be powered by unmodded off the shelf PSUs would be huge.

Where will you get your supply of custom chipsets? Do you want to reverse engineer Apple's already badly documented chipsets and reimplement them on fast enough FPGAs maybe even support more modern RAMs or improved off-chip caches? It would be nice to have a mATX NewWorld Mac you can maintain for playing old MacOS games, but the farther you go into the G4 (or even worse G5) era the more advanced GPUs you would have to reimplement as well. The PPC6xx era 2D on-board graphics may be in reach of such a project, but I can't see anyone without Nvidias active support releasing a Quadro FX 4500 compatible GPU clone.

Chipsets indeed prove a challenge, but it’s not insurmountable. QEMU’s emulation of a G3 tower is a decent example of this.

There’s decent availability of PCI and AGP GPUs supported by OS 9 and early OS X, especially if you include PC variants that can be flashed to work with Mac OS, so I wouldn’t worry about video too much in the short term… just make sure the motherboard has a PCI or AGP slot.

Maybe you could do a hardware version of that the emulation community does and say "this FPGA should act like a chipset X, here's how to program it, but don't ask us for the blob."