<i>Originally HT was supposed to be transparent.</i><p>According to whom? I don't think anyone with a clue would have suggested that. If you care about writing high-performance code, you care about the behavior of your processor. Obviously, multiplexing the execution of two program threads onto a single physical core is going to affect performance, whether in the form of scheduling differences, caching effects, etc.<p><i>they should have dropped HT and go for actual cores instead.</i><p>Well, you can do both, of course. If HT gets you better utilization of a single core, then fair enough. The question is really whether the transistors/power you burn on HT would be <i>better</i> spent on additional cores (or bigger caches, etc.).