FSB and Power Draw? (Same clock)

[friend'scatdied]

I want to get my Q9550 to run with as low of a power draw as possible. I'm going to be squeezing the Q9550 and an HD 5850 (which I will also undervolt as aggressively as possible) to a Shuttle 300W 80 Plus PSU (2 12V rails, 14A each for 28A total).

The lowest it will run is 1.025v in the BIOS, which translates to a vDrop of 0.98-0.99v in-OS and vDroop of 0.96v under load. This is with stock clock speeds (333MHzx8.5, 2.83GHz). This setting is OCCT stable for 9 hours (haven't tried more). I am fairly certain these settings will draw less power than the Q9550S that I was originally intent on purchasing (whose claim to fame is a VID of 1.16). The hottest core gets to about 57'C, with the rest at 52-53'C (linpack).

However, it will also run at 400x7 (2.8GHz) with the same settings, also OCCT stable for 9 hours. From what I am told the higher FSB will give marginally better performance even with the similar clock speeds. The temperature on the hottest core is about 3'C higher than with stock, at 60'C (rest of the cores are 54'C).

(Bear in mind my setup is in a Shuttle case with only one 92mm exhaust fan, which also functions as part of the CPU heatsink/fan unit [Shuttle I.C.E. cooler, which has 3 heatpipes and a modest number of fins]. I understand that they will be higher than you would expect with such an aggressive undervolt if it were in a roomy case with good airflow.)

Given that I am prizing low power draw, will the 400x7 setting draw more overall power than the 333x8.5 setting given that all other variables are held constant? I understand that the 400MHz FSB will put more stress on the NB, which could mean greater power draw there. However NB temps were the same under linpack load, and the MCH voltage is still stock.

I'm quite tempted to go back to 333MHzx8.5 because it seems it would be "safer," and also because my system does not reboot properly when I change any FSB/memory settings (even FSB raised by 1MHz or with a reduction in the memory divider to underclock the RAM).

 

[defaultluser]

I have two things to say about your problem:

1. the FSB is only a clock line: that is to say, unless you are utilizing the extra bandwidth granted by the FSB increase, your power consumption will not increase. Allow me to explain: if the signal sent to the processor (FSB clock) is increased, and thus the signaling rate (FSB) is increased, unless you use that extra bandwidth, it means power consumption is almost the same overall. You have to USE the bandwidth to draw more power.

2. the power increase from the slightly higher FSB is nothing compared to that you save by undervolting the processor.

I really don't see why you feel you need to mess with the FSB settings, why not run it at stock?

 

[obobski]

I really don't see why you feel you need to mess with the FSB settings, why not run it at stock?

because that PSU can't handle it under any circumstances

the higher FSB will increase performance, especially if you can step your memory up to match it 1:1, basically: it can communicate with everything else faster, so it can get more done (yes, like the Nextel commerical)

I'm really doubting if you're going to see any power savings though, as defaultluser said (KEKEKE I JUST GOT IT /dork), the undervolting does quite a bit more for power consumption reduction

as far as power consumption goes overall, that chip at stock with EIST enabled will sit at 2Ghz and something like .95 vCore the majority of its time, to help with power consumption and temperatures and so on, I'd probably just leave it at stock and be done with it unless you've got issues with overheating or the thing dropping and rebooting when you load up a game (that 5850 is gonna be more likely to cause this when it loads, as its power consumption goes up by something like 8x)

 

[engiNURD]

... I'm going to be squeezing the Q9550 and an HD 5850 ... to a Shuttle 300W 80 Plus PSU (2 12V rails, 14A each for 28A total). ...

If those rails are actually separated, each rail will only have 12x14=168W available. Now, the common allocation is one rail for the CPU, and the other rail for the rest of the system. The HD5850 alone will need 188W at full load. Better investigate more on that PSU to see if it really has 2 separate rails.

... as defaultluser said (KEKEKE I JUST GOT IT /dork) ...

heh, luser was the default login name for our lab computers when I worked at a uni.