red floyd wrote:
I've got a GA-880GA-UD3H, and an Athlon II X3 455.

I'm using a stock heatsink, and a 500W power supply. Unlocking the
CPU reveals a fourth core. Given the PS and the heatsink, should I
have any issues if the CPU is unlocked/


The CPU support chart for the motherboard, handles up to 140W processors,
so that's not going to be a problem.

http://www.gigabyte.com/support-down....aspx?pid=3789

The disabled core, was probably wasting power just sitting there.
When they're disabled, it doesn't mean they're not still connected
to VCore.

There was a proposal at one time, sort of a "what-if", to turn off
power on individual cores. But to do that, might require separate
race tracks (power rail rings) on the silicon die. And I don't
really think they like that idea too much. There is a limit to how
many race tracks you can have around the edge of the die. So I would
assume the locked core was still receiving power.

They could remove the clock entirely from that core, or use clock gating,
as other means of reducing power. But on modern silicon, that doesn't
necessarily reduce the power on that core to zero either.

My expectation would be, your idle power won't change, while
your 100% load power will go up slightly. I wouldn't expect
the change to be major.

*******

You need to test the "before" and "after" cases.

Ideally, you'd want test software, which tests execution of all
possible instructions. Intel and AMD will have these in-house
(after the FDIV bug, such applications are crucial, and should be
quite detailed in what they check). I'm not aware of anything like that,
available for end users. Only the factory can thoroughly certify the core
(with test vectors for 100% of chips, or software tests as a
functional test of correctness of design).

The next best thing, is to use an app that looks for execution
errors. As an old timer, I'd use Prime95 (stress test option),
as it does some math, and knows what the answer should be.

Prime95 makes the processor hot, so it also tests the adequacy of
the cooling system.

http://www.mersenne.org/freesoft (download page)

First, you'd run Prime95 on the three cores, without unlocking
the fourth. This establishes the baseline conditions for the
processor. You check CPU temp with Speedfan (almico.com), while
Prime95 is running. Prime95 starts a test thread per core, so
there will be three test threads for the baseline run.

You shouldn't get any errors, in a four hour run of Prime95, with
your three cores. You don't want any of the test threads to stop
on an error. If the test is clean after four hours, you can
stop it (stop, and exit).

If your processor isn't stable and error free with the three
cores, then stop right there. You're not ready to unlock.
Things would only get worse if you unlocked. You need to fix
the reason for the errors first, before you go any further.

During the test run, you note the temps, and whether the cooling
in your system is good enough. Say we aim for 60C or 65C as
an upper bound for the Tcase perhaps. (Tcase and Tdie can be
different, and you have to be careful not to freak out, by
measuring the wrong one and jumping to conclusions. The die
gets hotter than the case, and some measurement methods
are measuring the silicon die, which can be 25C hotter than
the casing.) On modern systems, the temp measurement
is more likely to be the silicon die kind.

So if the three-core run is error free, and there seems
to be some cooling margin, then you're ready to unlock.

Before unlocking, you back up your Windows C: drive. That
protects you in case the fourth core causes damage to
the Registry or the like, on the Windows partition. (Doing
the Prime95 tests with a Linux LiveCD, is a way to avoid this,
but then the temperature measurement step is more complicated.)

So with Windows backed up, you enable the fourth core, and do
another Prime95 run. Did one of the test threads stop ?
Did it stop quickly ? Perhaps the fourth core really stinks.
Or, if the four hour run passes with just as much ease and
the baseline run, you're home free. (Prime95 only covers a
fraction of all the possible instructions on the processor,
so someone at the factory would laugh at this test as an
"acceptance test". But what can we do ?)

I wouldn't expect the temp rise, on a Prime95 run with the
fourth core enabled, to go that much higher. As long as you
have a bit of headroom when three cores were running, it'll
probably be OK.

As for a 500W supply, that would only be an issue, if you
had a high end video card drawing over 200W. Then you
might be concerned. If you have a low end video card,
again, I don't expect a problem. If you really wanted
to know, you'd calculate an estimate of the system
power, to be sure. If your video card has no PCI Express
connectors on the end of it, for example, you've got
nothing to worry about. Such cards are 50W or less.

Paul