62 | MAXIMUMPC | NOV 08 | http://www.maximumpc.com
Voltage Tweaks
They say no pain, no gain. But it’s really no voltage tweaks, no high overclocks.
While the risks are great, overvolting can pay some great rewards
A reader recently asked us whether heat or
voltage was more dangerous to a CPU. Hands
down, we’d say voltage is far more dangerous.
All modern CPUs have a built-in limiter that
throttles the CPU if it overheats. The same is
not true when a chip receives more voltage
than it was designed for. Clearly, this is the
most dangerous part of mucking around in the
BIOS. If you’re faint of heart and don’t like to
break things, don’t mess with voltage tweaks.
However, if you’re looking for that extra bit
of performance, voltage tweaks are oft en the
only way to get there.
Modern motherboards will let you turn
all kinds of voltage knobs, but the basics are
CPU core voltage, RAM, and chipset.
If you read our sections on memory tim-
ing and speed, there’s one very important
fact you need to know: You’ll likely need
to overvolt your high-performance RAM
modules to hit their rated speeds. DDR400
offi cially tops out at 400MHz, and DDR2 tops
out at 800MHz. Anything higher is techni-
cally beyond JEDEC specifi cation and invari-
ably requires overvoltage to hit. In fact, you’ll
notice that much of the high-performance
RAM today will include recommended volt-
age settings needed to hit the clock speed and
timings it boasts.
DDR’s spec’d voltage is 2.5 volts. DDR2’s
is 1.8 volts, and DDR3’s is 1.5 volts. To give
you an idea of how much additional voltage
you need to overclock RAM, consider this:
To get a typical DDR2 DIMM to go from
DDR2/800 to DDR2/1066,
you have to push the volt-
age to 2.20 volts. To get a
DDR3 module to reach all
the way to DDR3/1800,
you have to push two
volts. If you ask us, that’s
an awful lot of voltage,
and your modules prob-
ably aren’t going to last
several years at those
levels. On the other hand,
what enthusiast is going
to run the same RAM for
fi ve years anyway?
Which bring us to the
age-old question: “How
much voltage do I run?”For RAM, we recommend that you follow the
manufacturer’s settings, as that will be the
best indicator of the module’s overclocked
speed and voltage needs. For CPUs, it’s chip
dependent. One way to judge how far you
can push your chip’s voltage is to cruise
forums at MaximumPC.com, Anandtech.com,
HardOCP.com, or any of the numerous forum
boards out there to see what people are
running for your particular CPU. One new
development we like is the danger gradations
in some vendor’s newer BIOSes.
Older BIOSes simply let you select howmuch additional voltage to add to the CPU
without any regard for the risk. Some newer
BIOSes will actually indicate by color how
hazardous your voltage increase is. Gray is
mostly safe while red indicates nuke poten-
tial. Since we fi gure the board engineers are
basing their threat levels on lookup tables
based on the CPUs themselves, we feel pretty
confi dent cranking up CPU voltage to just
below the red zone.
BIOSes today also let you increase volt-
age to the north bridge and south bridge
separately, and in most nForce boards, even
the HyperTransport link
between the north bridge
and south bridge can be
overvolted. Do you re-
ally need to do this? We’ve
found that, yes, you do need
to goose the north bridge
voltage on occasion to get
stable upgrades, but like
CPU and RAM overvolting,
it’s quite risky and can dam-
age the board when done
without caution. Take our
previous advice: See what
works for others before
jumping in with both feet.Most high-performance RAM requires running out-of-spec voltage on the modules.How you change voltage settings will vary greatly from board to board.OLD TECH, NEW TWEAKS