A core 2 quad is just 2 core 2 duos stuck together. As such 2 cores share a cache(4megs) and the other 2 share another(4megs)
I do not think you can power down cores.
Nope, not on desktop chips. Laptop chips have much lower sleep states (C4) that can pretty much do this, though.
Speed Step(clocks down and reduces voltage) and CE1(think thats what its is called....reduces voltage) will both lower power usage..... In my case this saves about 50-60 watts at idle
You shouldn't see such a drastic difference between idle wattage draws at full speed and full Vcore vs. idle speed and idle Vcore, especially not in an Intel CPU. At best, your Core 2 Quad goes from 2.93 GHz down to 1.67 GHz at idle and drops about 0.15 volts Vcore or so. I'd imagine a wattage savings of something nearer 20 watts than 50-60 watts. Now if you are talking about running the CPU at full-load under idle settings vs. full-speed settings (via setting power properties), then you should see a big difference like that.
But once any core is loaded they all clock back up. There is still a power savings at this time...
This is true with all K8 CPUs and desktop Core 2 Duos. However, the mobile Core 2 Duos have separate C-states for each core. It isn't apparent to me if the cores clock separately or not. Cpufreq says they do, but I can't find it anywhere in the Intel literature. So even if the core clocks and voltages are the same for both cores, the idle core will have parts shut off because of the C-states and save power. The AMD 10h family processors *do* have the ability to separately clock cores, even though the Vcore is the same for all cores. I assume they will have C-states that vary per core as well.
New cpus will be able to turn off cores(I think AMD Phenom is supposed to do this) and save allot of power(well more at lease). There are also some plans for cores running independent speeds to save power as well....
The higher C-states can shut off large parts of idle cores to save power. The C6 state in the Penryn Core 2 Duo mobile chips pretty much does shut off the core.
So in short the core2 quads are not that bad on power anyway....but new intel and amd chips will be better for power and heat.....
The current Core 2 Quads are pretty bad on power, to tell the truth. The slowest one is the Q6600, with a 105-watt TDP. That is pretty warm. The faster ones go up to 130 watts, which is as hot as the hottest Pentium Ds ever were. 65 nm is great for dual-core CPUs, with 3.00 GHz units from Intel using 65 watts and AMD's 6000+ using 89 watts. But it's a little premature for high-clocking quads. Intel has some quads with reasonable TDPs, such as the 50-watt Xeon 5300LVs and 80-watt Xeon 5300 series from 1.60-2.33 GHz. AMD also has some very reasonable quads, with TDPs of 68 watts up to 1.90 GHz and 95-watt TDPs to 2.00 GHz. Sure, they can push TDPs to 125 to 130-watt levels to get a few hundred more MHz, but I think that it would be smarter to wait for smaller process nodes or greater process refinement to start pushing speeds higher rather than raising the TDP ceiling.