> why not just use x86-64?
Uh, because you can't? It's not open in any meaningful sense.
The original amd64 came out in 2003. Any patents on the original instruction set have long expired, and even more so for 32-bit x86.
alt Hacker News
The original amd64 came out in 2003. Any patents on the original instruction set have long expired, and even more so for 32-bit x86.