Speculation has nothing to do with x86 in particular, although it has something to do with its general approach to execution (as opposed to e.g. the Mill CPU).

Speculation has nothing to do with x86 in particular, although it has something to do with its general approach to execution (as opposed to e.g. the Mill CPU). Speculation is part of out of order execution, which is logic to execute code passages when their inputs are ready, as opposed to strictly in program order, while maintaining the program visible effects of executing in program order. It works the same in ARM, MIPS etc. Not doing OOO execution roughly halves CPU throughput on your average code. AFAIK OOO without speculation is possible, but loses maybe half of its efficacy. Actual experts may want to correct my numbers.