If overclocking is the sport
of champions, a Black Edition AMD Phenom II X3 720 in your PC is akin to a 10
second lead on the competion. Like the Extreme Edition processors from
Intel, AMD's Black Edition chips are multiplier unlocked. That
critical bonus assures monster overclocking potential!
The AMD Phenom II X3 720 Black Edition runs at a default speed of 2.8
GHz, with its clock multiplier set to 14x. It can be overclocked
by raising the clock multiplier higher, and then raising the motherboard
reference clock speed. The reference clock generates the source signal to drive
all components on the motherboard, and with Phenom II processors it operates by
default at 200MHz.
For example: 14 (CPU multiplier) x 200 MHz
(reference clock) = 2.8GHz (CPU and memory controller speed).
As the multiplier for the Phenom II X3 720 processor is 14x, we can easily
overclock the chip just by changing this value to 15x or 15.5x. Adjusting the
multiplier to 15x automatically overclocks the CPU without modifying the
motherboard reference clock speed (akin to Intel's FSB), so the equation changes
to 15 x 200 = 3.0GHz. The benefit is that it allows us to use lower bus
speeds to attain a higher overall CPU clock speed, thus reducing
the need to run the memory as fast.
To start the memory was set to DDR2-800 mode and the motherboard
frequency was overclocked in 25MHz increments. For the time being the Phenom II
X3 720's CPU multiplier was left at 14x. The socket AM3 Phenom II X3 720
easily handled 225MHz, 235MHz, and 245MHz which yielded a
processor clock speed of 3.43GHz. Beyond this (ie 255MHz) the system became
unstable and wouldn't post.
CPU-Z 1.49 recognizes the Socket AM3 Phenom II X3 720,
overclocked settings highlighted in red.
For the next attempt we reset the motherboard reference clock back to
200MHz and changed the CPU multiplier from 14x to 15x, then set about increasing
the Bus speed once more. Without much effort the motherboard was once again
running at 245MHz, resulting in an overclocked speed of 3.67GHz for the AM3
Phenom II X3 720 Black Edition (default is 2.8GHz). To get beyond this point
PCSTATS increased CPU vCore from 1.3V to 1.525V and this allowed us to boost
motherboard reference clock speed from 245MHz to 250... 255.. and 260MHz...
nope. Since the 260MHz Bus speed wouldn't POST we lowered things back to 255MHz,
or a CPU speed of 3.82GHz! That's a 1200MHz overclock on the Phenom II X3 720
Black Edition CPU!
Unfortunately, while the system would POST just fine, Vista blue screened at
that speed. Eventually after a few minutes of trying different voltage mods,
PCSTATS settled on an overclocked speed of 15x multiplier, 245MHz motherboard
reference clock for an overclock of 3.675GHz. We tried a few settings
above this, but stability could not be guaranteed. That's quite a nice healthy
overclock of 875MHz above the stock clock speed of 2.8GHz!
It's time to take off the kid gloves and see how fast this triple-core
processor really is!