This is really sad. The world is heading to a duopoly x86 - arm. Alpha is dead, Mips is almost dead, PA-RISC is dead, POWER is too expensive and RISC-V is mostly nice to have.

A lot of these architecture have some drawbacks in modern times.

Alpha’s loosey-goosey memory model makes multithreaded code on SMP systems more challenging. Linux utilizes its Alpha port as a worst-case testbed for data race conditions in its kernel.

SPARC’s register windows are anachronistic and complicate the implementation of CPUs, and I’d guess also make it more difficult to build OoOE cores (so many SPARC chips are in-order, why?)

POWER isn’t so bad though. It’s open enough where you could build your own lower-cost core if you wanted. There’s nothing intrinsic to the ISA that would mandate an expensive chip other than volume constraints.

PA-RISC put up some great numbers back in the day but between the Compaq acquisition (bringing with it Alpha) and Itanium it was chronically under-resourced. They had a great core in the early 90s and basically just incrementally tweaked it until its death.

classichasclass

You could even build your own Power ISA system with Microwatt, which is fully synthesizeable and growing by leaps and bounds.

https://github.com/antonblanchard/microwatt

(Disclaimer: minor contributor)

I really liked PA-RISC. I thought it was a clean ISA with good performance at the time and avoided many of the pitfalls of other implementations. I think HP didn't want to pour lots of money into it to keep it competitive, though, and was happy to bail out for Itanium when it was viable. My big C8000 is a power hungry titan, makes the Quad G5 seem thrifty.