Quote Originally Posted by Helmore View Post
And what if AMD could clock an 8 core (4 modules) Bulldozer at 5 GHz while only consuming 95 Watts? And it does this while having about 95% of the IPC of AMD's current Phenom II chips. That's what I'm getting at. IPC is only part of the story.

I'm not claiming that Bulldozer will be anything like that, just that there's more than just IPC to getting great single threaded performance.
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IPC and frequency are conflicting aproaches. You can't have both, it's one or the other. Your theoretical Bulldozer is like having a Pentium 4 with the IPC of Core 2. Pigs will learn to fly sooner than you will get such a CPU.

To get a lot of IPC you need very wide cores with lots of execution units, complex decoders able to extract the parallelism out of the instruction stream and lots of buffers to keep a mountain of data in flight through the chip. All that limits the frequency you can get. In other words, if your goal is IPC, you give up on frequency. Complex circuits clock badly and burn a lot of power.

The best example is Itanium. Extremely wide, has typically 1.5-2x the IPC of Core/Nehalem but also clocks 2x as low. That's inspite of the fact that Intel trying to reduce complexity as much as possible, by making it in-order and moved the task of finding parallelism out of the chip and into the SW ( compiler ).

The other aproach is frequency. Netburst is a fine example, make it as narrow as possible, have half or two thirds of the execution units of other CPUs, but clock as high as possible. Do some clever stuff to hide cache miss penalty and raise unit utilizsation ( SMT ) and you have a speed racer design. IPC can't be high, you have fewer decoders which are simpler, few execution units and miss rate penalties are huge.

Middle aproach is a beefed up Nehalem, the current one leans more to the fat core, high IPC, than speed racer. Altough if you optimize it by hand as Intel does, you can get some impressive frequency too. But that's only possible if you have a few hundreds years of manhours available.