order of business in this underclocking experiment was to determine the
lowest core voltage at which we could successfully benchmark each separate
speed grade of the Athlon64 processor. The BIOS settings of the
DFI Lanparty motherboard were used to lower the Core voltage and CPU
multiplier at each step and a combination of SuperPI, 3Dmark2001SE
and 3DMark2005 provided the benchmarks. The Prime95 burn-in
program was also used to test operating stability at each voltage
Starting at the Athlon 64 4000+'s default clock
speed of 2.4GHz, default multiplier of 12x200MHz and default core voltage of 1.5V,
the core voltage was lowered to 1.4V. This proved to be the lowest stable
voltage the processor would accept at stock speeds. A temperature reading
was taken at full load during the Prime95 test, then the set of three benchmarks
The multiplier was then dropped to 11.5x200MHz,
reducing core speed to 2.3GHz and voltage was set to 1.35V. The system
proved to be unstable at this point, so voltage was set back to 1.4V and
temperature readings and benchmarks taken.
The core speed was then dropped to 2.2GHz and core voltage
to 1.35V and we continued to stress test and benchmark the system, lowering
core multiplier in steps and determining the lowest stable voltage for each.
The results are listed below.
|Temperature under Load by
||Temperature under Load (C)
*All temperatures were measured using a Fluke digital thermometer and thermocouple
probe placed on top of the copper base of the heatsink. This gives a
good idea of the temperatures the heatsink was radiating into the
case. The ambient temperature was approximately 22 degrees Celsius.
While there was a noticeable drop in
temperature, it was not a huge one. From 2.4GHz to 800MHz, the
temperature decreased by only 6.5 degrees Celsius. To put it another
way, for a 66% drop in speed there was a 6.5 degree drop in
temperature. This makes a bit more sense if you look at the numbers
in terms of Voltage not speed; a 43% drop in voltage producing a 6.5 degree drop in temperature seems more reasonable. The largest temperature drop occurred
between 1.3V and 1.25V, where the temperature fell almost 1.6C.
The Athlon 64 4000+ can run stably at a fraction of its original
voltage and clock speed, which was interesting to see, but how much CPU
power was sacrificed in doing this?
Let's take a look at the
performance benchmarks on the next page.