What's the effect of the Graphic card setting on an FSB overclock?

ericvaughn26

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Dec 9, 2016
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Let me just state one caveat to my question. I know my hardware is relatively ancient, but it's all I have. I have a Dell OptiPlex 755 with a Core 2 Quad CPU Q8400. I was running a Nvidia GeForce 6800, and I was able to overclock my Core 2 Quad from 2.6Ghz to 3.0Ghz with almost no CPU temp increase. My old Nvidia bit the dust, and I bought an older Dell ATI Radeon HD 4550, which greatly improved the graphics across the board. But . . . now I can't overclock at all. Nothing changed except for the graphic card swap. Even a 01 increase in frequency crashes the computer. What gives?
 
It is probably becouse there is a higher power draw from the new GPU and you are hitting the power supply limit with the overclock.....Just my thoughts and it could be something else..

What power supply?

Hopefully someone else can jump int.
 
What OC method were you using? Which size Opti 755 do you have? Some of the smaller ones have a PCIe slot power limit that may be coming into play here. Those support the Q9650 95W CPU so 3Ghz shouldn't be an issue. How are you powering the GPU? Optis don't have PCIe power cables. Does that GPU need one?
 

ericvaughn26

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Dec 9, 2016
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Thanks for the replies.

I am using the same overclocking app (setfsb) on both cards.
I have the 755 Desktop model
It has one PCIe slot rated (printed right next to the slot) as a 25 watt limit.
My new DELL ATI Radeon HD 4550 is rated the same 25 watts. The previous display card Nvidia GeForce 6800 is old enough that I'm having trouble finding a spec sheet online, but it worked with no issues other than being slow. But it was still 2 or 3 times faster than the imbedded graphic controller. The new DELL ATI Radeon HD 4550 is magnitudes faster than the GeForce 6800. Neither card requires a separate power connection.

Oh, I forgot to mention that I have an external 400 watt Power Supply, meaning I bought a PS harness that extended the length of the 400 Watt PS's cables enough for me to place the PS on the desk outside the rear of the computer. It performs just fine. Probably more than I need, but the 260 watt Power Supply that comes with this computer worried me so much, I just went ahead and installed the 400 Watt PS. I installed a large case fan where the power supply used to be to retain any air flow that the PS's fan might have provided.

I think that's it.

Eric
 
You can get that OC with a piece of tape on the Q6600.
http://www.tomshardware.com/answers/id-2125877/tape-mod-bsel-mod-intel-q6600.html
Some people report success ignoring the 25W limit. But the risk is up to you. If it's all you have it might not be worth it.
That optiplex has a 95W CPU limit, and with those GPUs 260W is more than enough. But if you already have 400W then good for you.
Here's a secret Optiplex DT mod. The right angle PCIe riser to run a short full height GPU in those.
https://www.ebay.com/itm/0G5459-Dell-GX755-PCI-PCI-E-Riser-Board-Genuine/173339956989?hash=item285bddd6fd:g:84oAAOSw4A5Y2Va0
 
The trick is to start with a CPU that has a low FSB. Unless you have one of the X38, or X48 chipset MB that support 400fsb then no. Also the pinmod would be a different pin. The Q8400 is already 333fsb, the tape would do nothing.
In Quad cores 266 fsb=65nm quads, and 45nm=333fsb. In the Dual cores a 45nm 266fsb E7500 can be taped to 3.66GHz.
Just to be thorough yes the QX6850 is 333fsb and 65nm, and a total wasye fo time compared to the QX9650.
 

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