3 ms·
They could have wired those instructions as a NOP, rather than aliasing another opcode...
by anticensor 3y ago
They could have wired those instructions as a NOP, rather than aliasing another opcode...
- Someone 3y agoThey could, but transistors were expensive at the time. Why spend valuable space making sure all instructions are well defined? On modern CPUs designed for multi-processing and protected memory, you don’t want some instructions to accidentally cross privilege boundaries (can’t have an ‘illegal’ opcode accidentally be non-privileged and modify some privileged processor state), so you have to do some of that. Transistors also are cheap, so you can afford to.