Things change. Windows cut out 16-bit code with 64-bit Windows, so that particular half of the last "half century" is gone. Macs transitionedto different archit

Things change. Windows cut out 16-bit code with 64-bit Windows, so that particular half of the last "half century" is gone. Macs transitionedto different architectures several times, iPhones to some extend too (from armv7 to armv8, dropping arm32 support entirely relatively early after). The various Rosettas, most recently the x86-to-ARM one, showed that software emulation is always an option, and so does WoW64, which is a part of ARM Windows (and a part of x86-64 Windows, but there it's not really a software emulator). > I expect the ARM world will also be singing a similar tune in several decades' time, when backwards compatibility with ancient ARM binaries become steadily more important than pursuing the next new shiny at any cost. I am not so sure at all about that. The reason is that half to a quarter decade ago, even normal application code was very close to the metal, with MS-DOS basically being a glorified bootloader with file system services that loaded little mini-OSes calling themselves DOS applications. We are far, far away from that world. Mature abstractions make ISA transitions more and more painless for end-user application developers. The exponential advances in speed make software emulation well feasible for the remainder. High-performance stuff will want to take advantage of the new architectures anyway.