@David Bond

In about 15 years programming and sysadmin-ing I have never heard of 'superthreading'.

Traditional threaded software allows each thread to do what ever the programmer codes the thread to do: is assumes that any given thread runs on a general purpose processor and any given pair of threads do not have a relationship qua the instructions they send to their CPU modulo sync of data access. Which means if several threas want to all do floating point ops that is fine; or if they want to do all integer ops that is fine too; if they want to do some mixture that is fine also.

HT was (may be again?) a way to exploit that a P4+ CPU has more execution units than can strictly speaking be used simultaneously by single threaded code. Thus, if a programmer or compiler could conspire to issue instructions that could execute (1) on the FP unit and (2) the integer or load/store unit, then there was no reason not to send both to the processor.

But HT failed if the two above instructions had a dependency between them. HT actually had a long list of what the two instructions could not admit in terms of there relation to each other. SO HT was not threading. HT was crafted code, in much the same manner as programming CUDA or CELL is: if your algorithm fit the model then you were in business... but the model was quite restrictive, one did not just pass the compiler a switch telling it to produce HT code and magically get two threads of execution. One really had to structure one's code to meet HT's requirements regardless of the compiler option.

Few people did it: the people that just passed the compiler the option got noothing in particular for their effort: people that spent the time to understand HT model and their code got results directly related to whether thir algo's could be HT-ized. It was not a general fix, it was not even anything like an easy fix.

As for statements like "Superthreading requires all execution instructions be from the same thread", well my friend, that does not even make sense. Who is signing that cheque you get each quarter?

@lennie

I have been a fan of the 486DX2, the cx686-p166+, the AMD 586 & 686, the Pentium II, the Pentium III, the Athlon, the XEON, the Athlon 64, the Opteron, the XEON in that order.

Lately I am enamoured of those 45nm 1333MHz FSB XEONs.

I guess that makes me a Cyrix fanboy.

Marketing - HT in this case - is marketing, and should be identified as such whether it is Intel or AMD foisting it in the public.