> I don't think there have ever been an OoO CPU without speculation.
To the extent I've looked at it, without reading original documents, the original OoO design that current systems are based on, the IBM System 360/Models 91 and 95's floating point unit using Tomasulo's algorithm https://en.wikipedia.org/wiki/Tomasulo_algorithm didn't extend to speculative execution.
No doubt because gates were dear, implemented with discrete transistors, and that processor was a vanity project of Tom Watson Jr's. And memory was slow, core except for NASA's two 95's with 2 MiB of thin film memory at the bottom, and cache was still a couple of years out, introduced with the 360/Model 85. OoO becomes compelling when you have a fast and unpredictable memory hierarchy, as we started to have in a big way in the 1990s when we returned to this technique.
Interesting. It seems that the machine did have some limited form of branch prediction, but probably the expectation was that FP kernels would be optimized to be mostly branch free, and, as you say, transistors were a premium.
To the extent I've looked at it, without reading original documents, the original OoO design that current systems are based on, the IBM System 360/Models 91 and 95's floating point unit using Tomasulo's algorithm https://en.wikipedia.org/wiki/Tomasulo_algorithm didn't extend to speculative execution.
No doubt because gates were dear, implemented with discrete transistors, and that processor was a vanity project of Tom Watson Jr's. And memory was slow, core except for NASA's two 95's with 2 MiB of thin film memory at the bottom, and cache was still a couple of years out, introduced with the 360/Model 85. OoO becomes compelling when you have a fast and unpredictable memory hierarchy, as we started to have in a big way in the 1990s when we returned to this technique.