PC running at half speed

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I have a PC here that should be 2.4GHz but I can only get it to run at
1.2GHz. It's running at 100MHz x 12 when I believe it should be running at
200MHz x 12. It appears that board supports my CPU but it's hard to tell
with there being so many P4s on the market. I have installed the latest bios
with no luck and tried different ram. All the ram is pc3200. I have tried
different CPU settings in the bios but setting it to 200Mhz FSB causes it to
not boot and I have to reset the bios.

Anyone got any ideas?

Thanks in advance,

Motherboard GA-8PE667
A cpu support list is here:

CPU 2.4GHz P4
Details here:

Re: PC running at half speed

Michael C wrote:
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The motherboard uses an 845PE Northbridge. You'll notice, in the
CPUSupport page, the FSB800 processors are "N/A" as in "Not Applicable".

If you plug an FSB800 processor into the board (which would normally
use a 200MHz input clock), one possibility is the clock generator will
supply 100MHz. 100*12 = 1.2GHz and thus your half-speed symptoms.

The fastest processor using perfectly "stock" settings on an
845PE, is a 3.06GHz/FSB533 Northbridge. It was one of the
first Northbridge processors to support Hyperthreading.

Asus has an 845PE based board as well, called the P4PE. Asus
decided to support overclocking of that chipset on their board.
The motherboard has limited hardware support at FSB800. It would
only allow a single stick of memory to be used (because the
memory would run at DDR400). A typical user result, was the
board wasn't perfectly stable at FSB800, and turning it down
just a little bit, like FSB796 (input clock 199Mhz) or the like,
would be enough to fix it. What that tells you, is the
official chipset rating of FSB533, is capable of running
a bit faster.

Whether it is wise to try cranking the clock, really depends
on whether the PCI and AGP clocks are "locked" or not. A locked
clock situation, means the PCI is 33MHz no matter what, and the
AGP is 66MHz no matter what. The bus clocks are independent of the
CPU input clock, when the "clock is locked".

In the unlocked case, the PCI and AGP clocks are divided down
from the CPU input clock. For example, 200/6 = 33.3MHz might be
a divider choice inside the clock generator for the PCI bus. The
divider in that example, "6", is maintained over a range of CPU
input frequencies. The problem comes, when the choices are too
aggressive. For example, say the clock generator went all the
way to 240MHz, and 240/6 = 40MHz for PCI. That would cause the
PCI bus to fail, and may cause an IDE drive which derives a
clock from the PCI clock, to corrupt. So when people overclock
the older motherboards, they have to be very cognisant of the
(undocumented) divider choices buried in the hardware. When
doing such testing, you don't test by booting Windows from
your hard drive. Instead, your first test is to try booting
something like a Linux LiveCD, as the CD may have no dependence
on any hard drive. And if the IDE cable clock is wrong, the CD
will survive as it is read-only.

To get past 1.2GHz, you're going to have to go into the
BIOS and change something. Your current CPU input clock
(using "Auto" presumably) is 100MHz. The BIOS may offer
133MHz, which will give you a quick boost in the right
direction. You could simply push the thing to 200Mhz,
but there is no point trying that unless you
at least strip down to one stick of PC3200 RAM. The
845PE cannot drive a heavy load at DDR400 speeds, at
least according to the advice from Asus. After all,
that is an overclocked condition for the chipset.
Intel didn't intend to run it that way.

And the options are also dependent on the clock generator
hardware chip. I'm assuming it actually has options
to run up to 200MHz.


Re: PC running at half speed

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Oh dear, I feel really silly now. :-) I just saw the CPU there and thought
that meant it was supported, I didn't even see that last column. I have to
give gigabyte full credit as they are one of the few vendors who say what
their products won't do. I have another P4 machine, I might be able to just
swap processors and hopefully both will support each processor (if I'm

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It does appear to support this feature.

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I tried 200MHz and it didn't boot. The problem is I have limited support for
memory multiplier, only 2.0 or 2.66.

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It will run up to 350Mhz in increments of 1 but I think it all sounds like
too much trouble, I'll just find a board or cpu that fit together.

Thanks for your considerable time replying.


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