Comment by KK7NIL

> The shift from 16-bit to 32-bit protected mode with the Intel 80386 processor that fundamentally altered how the processor managed memory.

I said x86 has "over 30 years of backwards compatibility". The 80386 was released in 1985, 40 years ago :)

> Intel 80286 introduced a 24-bit address bus to support more memory, but this broke the address wraparound behavior of the 8086.

This is the only breaking change in x86 that I'm aware of and it's a rather light one as it only affected programs relying on an exactly 2^16 memory space. And, again, that was over 40 years ago!

> The shift to x86-64 that Microsoft had to compensate with emulation and WOW64

No, I don't think so. A x86-64 CPU starts in 32 bit mode and then has to enter 64 bit mode (I'd know, I spent many weekends getting that transition right for my toy OS). This 32 bit mode is absolutely backwards compatible AFAIK.

WOW64 is merely a part of Microsoft's OS design to allow 32 bit programs to do syscalls to a 64 bit kernel, as I understand it.