PDP-11 was a major source of inspiration for m68k architecture designers. The influence can be seen in multiple places, starting from the orthogonal ISA design down to instruction mnemonics.

It is quite likely that not allowing the misaligned access was also influenced by PDP-11.

PDP-11, m68k – to name a few, did not allow misaligned access to anything that was not a byte.

Neither are RISC nor modern.

If I'm not mistaken, microcode is a thing at least on Intel CPU's, and that is how they patched Spectre, Meltdown and other vulnerabilities – Intel released a microcode update that BIOS applies at the cold start and hot patches the CPU.

Maybe other CPU's have it as well, though I do not have enough information on that.

> In Linux the default swap behaviour is to also swap out the memory mapped to the executable file, not just memory allocated by the process […] I believe both Windows and macOS don't swap out code pages, so the applications remain responsive, at the of (potentially) lower swap efficiency

Linux does not page out code pages into the swap. You might be conflating page reclamation with swapping instead.

In Linux, executable «.text» pages are mapped[0] as file-backed pages, not anonymous memory, so when the kernel needs to reclaim RAM it normally drops those pages and reloads them from the executable file on the next page fault once they are accessed again (i.e. on demand) rather than writing them to swap.

In this particular regard, Linux is no different from any other modern UNIX[1] kernel (*BSD, Solaris, AIX and may others).

[0] Via mmap(2) in argv[0], essentially.

[1] Modern UNIX is mid-1990's and onwards.

> In 1970 it might have been the only way to provide a flexible API, but nowadays we have a great variety of extensible serialization formats better than "struct".

Actually, fork(2) was very inefficient in the 1970's and for another decade, but that changed with BSD 4.3 which shipped an entirely new VMM in 1990 in 4.3-Reno BSD, which – subsequently – allowed a CoW fork(2) to come into existence in 4.4 BSD in 1993.

Two changes sped fork (2) up dramatically, but before then it entailed copying not just process' structs but also the entire memory space upon a fork.