[Q9450 / GA-EP45-DS3R] Underclocking Problems


[H]F Junkie
Jul 27, 2006
Don't ask why I want to do or try this, but I'm trying to underclock my Q9450 to 800MHz (8x100). Here is my hardware:

[Motherboard] GIGABYTE GA-EP45-DS3R Intel P45 Core 2 Quad/Core 2 Extreme/Core 2 Duo/Pentium/Pentium Extreme Socket 775 1600 MHz PC2-9600 (DDR2-1200) ATX
[RAM] G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1000 (PC2 8000) Dual Channel Kit
[CPU] Intel Core 2 Quad Q9450 Yorkfield 2.66GHz 12MB L2 Cache LGA 775 95W Quad-Core
[Case] Cooler Master RC-690-KKN1-GP Cooler Master 690 No P/S
[PSU] Corsair Memory CMPSU-750TX 750W TX750W ATX12V
[Video Card] VisionTek 900241 Radeon HD 4850 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported

BIOS Settings for Clocking:

Robust Graphics Booster = Auto
CPU Clock Ratio = 8 X
CPU Host Frequency = 100
PCI Express Frequency = 100
C.I.A.2 = Disabled
CPU Clock Drive = 800
PCI Express Clock Drive = 900
CPU Clock Skew = 0
MCH Clock Skew = 0
(RAM)Performance Enhance = Standard
(RAM)Extreme Memory Profile(X.M.P.) = Auto
(RAM)(G)MCH Frequency Latch = 400
(RAM)System Memory Multiplier (SPD) = Auto
(RAM)DRAM Timing Selectable (SPD) = Auto
(RAM)Timings = 5-4-4-12
(Voltage)CPU Vcore = 1.27500
(Voltage)MCH Core = 1.100
(Voltage)DRAM Voltage = 2.040
(Voltage)Everything Else = Normal
Limit CPUID Max. to 3 = Disabled
No-Execute Memory Protect = Enabled
CPU Enhanced Halt (C1E) = Disabled
CPU Thermal Monitor 2(TM2) = Enabled
CPU EIST Function = Disabled
Virtualization Technology = Enabled

I can adjust the multiplier from 6 to 8, and the CPU FSB from 100 to 1200. Based on this, I could set it to 6x100, but I personally prefer 8x100 for my scenario. The problem?

200x8 (1600) runs fine.

100-199 x8 will have problems.

100x8, after the motherboard tests those values, will bring me an error saying that I can't use those settings because of overvolting/overclocking being too "wrong" or something.

125x8 (1000) will work without error, the motherboard will accept these values, but at the boot screen it will show 200x8 (1600) instead of 125x8 (1000) -- even though if I go into the BIOS it will show I have 125x8 (1000) configured on the CPU. In fact, the motherboard doesn't even inform me of any problem with using 125x8 for clock settings, if there was one.

I am using 1.27500V on the CPU, and I have tried lowering the voltage to around 1.1V in attempt to get 100x8 (800) working, but the motherboard will only throw me that overclocking error message after it tests the values.

At 400x8 the RAM frequency is at 960 MHz. I think, based on the settings I have my motherboard set to, each MHz on the CPU FSB is worth 3 MHz on the RAM. And last I saw, the ratio of my clock in Everest or something was some high number like 13:21 or something. Is this a problem?

How can I efficiently be overclocked to 3.2 GHz -- and also achieve the underclock of 800 MHz that I so desire? What is bottlenecking me? And why is it that the motherboard will accept 125x8 without complaining, but still operate at 200x8? o_O

I haven't had a strange problem like this in ages. My mind is boggled and I'm wondering why things are working like the way I explained.

Irrelevant notes to self: RAM @ 2.1V for 4-4-4-12. Some have volts to 2.2V. Try for 1000MHz; 1066MHz did not work last time I tried. Someone has theirs at 1033MHz w/o problems. Someone did 4-4-3-15, another managed 1066 @ 2V. "Do not think they are 800 and unstable at 1000 because you did not bump the voltage!" "I have mine running in sync at 800MHz 4-4-3-10-1T 2.25V" Careful @ 2.25V -- should put fans on RAM if I go this high. 4-4-4-12 @ 2.2V. "Installed in a GIGABYTE GA-P35-DS3R with an Intel E8400 CPU overclocked to 4ghz with minor increase on CPU voltage. I can overclock to 4.4ghz in this combo but prefer a silent PC instead of the extra heat and noise it would take to run just a little faster. No application I run needs the extra 400mhz." -- How does someone manage to do this!?


Supreme [H]ardness
Aug 25, 2006
200x8 (1600) runs fine.

100-199 x8 will have problems.
Off hand I would guess that since the lowest per Intels specifications for that chipset FSB clock supported is 200MHz anything below that likely causes strange things to happen. I took a look at the datasheet and there is nothing about operation below 200MHz either good or bad but there are a lot of signals on the Host (cpu) side of the MCH buss that requires pretty specific timings. Still I found nothing to say it would not work just nothing that said it should work either. Sorry not much help but at least you can rule out finding an answer in the datasheet for the chipset.