> Multi-core support... was early requirements...

Erlang's first release was in 1986. Experimental SMP support was added to the Erlang VM in OTP R11B in mid 2006[0]. That's twenty years.

If you were to go back to the time of R11B's release and asked the folks who were aware of it "Has SMP support been added early in the life of the Erlang project?", I expect you would be hard-pressed to find anyone who would answer that question with a "yes". Twenty years after a software project's first release is a pretty damn long time.

If we want to be maximally charitable to you, then we can knock that date back to when the master's thesis work was started (and abandoned) in 1998. That's still more than a decade after the initial release.

It is my understanding that SMP support was a substantial change to the VM, and has gotten more complex as it has been made to perform better and better on larger systems and workloads.

> ...clustering was early requirements...

You are apparently unaware that the way operators who used Erlang handled multi-processor machines was to run multiple independent instances of the Erlang VM and -if desired- use local-machine clustering for intra-instance communications. SMP support is not the same as UP support with local-machine clustering of otherwise-independent program instances.

> Could you be more explicit about what you think has become more complex?

A great many things. The ones that immediately come to mind are SMP, HiPE [1], BeamAsm, dirty schedulers, multi time warp, and Unicode support. You may argue that surely some of the additional complications that have been added since 1986 are not much complication. I would counter that surely some of the optimizations that have been made since 1986 have not been much optimization.

[0] <https://erlang.org/euc/08/euc_smp.pdf>

[1] Unless I'm confused about HiPE... and the native code it produces was already a thing that the Erlang VM could consume. If that's the case, than the obvious complexity of HiPE is all outside Erlang. But the caveats on section 4.1 and 4.2 and acknowledgements in section 6 of [2] make me fairly confident that HiPE was not using already-existing functionality in the Erlang VM.

[2] <https://user.it.uu.se/~kostis/Papers/erlang03.pdf>

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