>> I mean server and backend systems, HPC systems

In HPC x86-64 (in fact, Intel x86-64) is the only thriving architecture: here is the breakdown from the last Top500:

- 445 systems are Intel x86-64

- 21 systems are AMD x86-64

- 19 systems are IBM Blue Gene/Q. IBM discontinued the Blue Gene line, so these systems would be replaced with something else as they age.

- 7 systems are IBM Power 7. There are no IBM Power 8 systems on the list.

- 7 systems are SPARC-based. AFAIK all of them are Fujitsu systems installed in Japan, and they are not accessible to researchers outside of Japan.

- 1 system is based on Chinese ShenWei architecture.

- There are no ARM (neither ARMv7 nor ARM64) systems on the list.