I think your conflating OoO and speculative execution. It was OoO which the itanium architects (apparently) didn't think would work as well as it did. OoO and b

I think your conflating OoO and speculative execution. It was OoO which the itanium architects (apparently) didn't think would work as well as it did. OoO and being able to build wide superscaler machines, which could dynamically determine instruction dependency chains is what killed EPIC. Speculative execution is something you would want to do with the itanium as well, otherwise the machine is going to be stalling all the time waiting for branches/etc. Similarly, later itaniums went OoO (dynamically scheduled) because it turns out, the compiler can't know runtime state.. https://www.realworldtech.com/poulson/ https://www.realworldtech.com/poulson/ Also while googling for that, ran across this: https://news.ycombinator.com/item?id=21410976 https://news.ycombinator.com/item?id=21410976 PS: speculative execution is here to stay, it might be wrapped in more security domains and/or its going to just be one more nail in the business model of selling shared compute (something that was questionably from the beginning).