deus maximus said:
Hi,
Can I easily o/c the 3.4 GHz Prescott on this board with
memory SPD 2.5 2 3 5 ? I have tried it at 3.5GHz but it is
unstable .It seems any increase in bus speed, even if I put
memory at 400MHz in bios is unstable. Is there more I can
easily do ?
Get a copy of CPUZ from
www.cpuid.com and verify the
frequencies being used. Make sure when you set the
memory speed, that the control is doing what you think
it is doing. On my P4C800-E, the DDR settings are
scaled by the amount of the FSB overclock. While your
BIOS may be attempting to show the true speed, check with
CPUZ and make certain.
There are three dividers available on that generation of
Northbridges. They are 1:1, 5:4, 3:2. If you RAM is
having problems, then the 5:4 ratio will drop the RAM
speed a bit with respect to the FSB.
FSB Ratio Memory
FSB800 1:1 DDR400
FSB800 5:4 DDR320
FSB800 3:2 DDR266
If you were to lift the FSB from FSB800 to FSB1000, the 5:4
divider would give a resultant DDR400. If you were to go
from FSB800 to FSB1200 (not likely), the 3:2 divider would
give you a resultant DDR400. By using the dividers, it is
possible to keep the RAM closer to its clock rating, as you
increase the FSB.
When overclocking, at some point you'll need a little
extra voltage for Vcore and VDimm. Setting VDimm to 2.7V
or so, should be safe with just about any memory. To go
higher than that, consult the manufacturer's spec sheet to
see what range they use. (Some chips, like Winbond BH-5,
are known to be tolerant of extreme voltage. Other chips
will burn up overnight at such voltages, so knowing the
type of chips is important when selecting a voltage. As
a rule, Asus motherboards don't give such dangerous voltages,
and you'd need something like an OCZ DIMM booster to get
into real trouble.)
To see the effect of processor voltage on overclockability,
try this database. Select your processor type, to see some
posted overclocking results:
http://www.cpudatabase.com/index.cfm?action=search
What I like to do with this data, is a scatter plot of voltage
on the X axis and frequency on the Y axis. Plot all the data
shown for your processor, throw out the ridiculous values,
then draw a best fit line through the remaining data points.
That will show you roughly how many hundreds of megahertz an
increase of 50mV or 100mV on the processor will buy you.
A processor datasheet from this page, will show you the
"Absolute Max" for the various processors. While Asus BIOS
generally don't allow huge overvolting on Vcore, it is a
good idea to understand how much room you have with respect
to the voltage.
http://developer.intel.com/design/Pentium4/documentation.htm
Paul
