AMD Phenom II X2 555BE: unlocking extra cores and staying within 95W TDP?

[jaydee]

Not sure if this belongs in CPU/Overclocking, Motherboards, SFF, or General Hardware. Mods can move if they wish.

I'm interested in building a mini-ITX system with a motherboard that only allows up to 95W TDP CPUs. I really only need a fast dual-core as my most intensive program is single-threaded still, so I'm pretty set on the $88 Phenom II X2 555BE that's 3.2GHz stock. I would probably lightly overclock on stock voltage to ~3.5GHz, but not interested in overvolting and the motherboard probably wouldn't like that very much anyway.

My main question is, if I were to unlock the 3rd and or 4th core, what would that do to my TDP? Would I have to undervolt/underclock in order to keep within the motherboards power envelope? Below are links to what I'm thinking of using so you have an idea about what I'll be working with. Thanks!


ASUS M4A88T-I Deluxe AM3 AMD 880G HDMI USB 3.0 Mini ITX AMD Motherboard
http://www.newegg.com/Product/Produc...82E16813131659

AMD Phenom II X2 555 Black Edition Callisto 3.2GHz
http://www.newegg.com/Product/Produc...82E16819103846

Scythe SCSK-1100 100mm Shuriken Rev. B 3 Heat Pipes CPU Cooler
http://www.newegg.com/Product/Produc...82E16835185097

LIAN LI PC-Q11B Black Aluminum Mini-ITX Tower
http://www.newegg.com/Product/Produc...82E16811112297

 

[fffblackmage]

I think you meant PhII II X2 555BE, since that's the one that has the 3.2GHz stock freq.

Essentially, the 555BE is an 955BE but with two cores disabled.

At least looking at the wiki list of PhII processors the 555BE has a 80W TDP and the 955BE has a 125W TDP.

 

[jaydee]

You're right, I meant Phenom II X2 555BE, fixed my original post.

I see on newegg, that the AMD Phenom II X4 945 Deneb 3.0GHz is listed at 95W TDP, so does that imply that if I'm able to unlock two more cores, I can stay within the motherboards limits by bumping the clock speed down to 3.0Ghz? Or am I being too simplistic?

 

[mfenn]

You're right, I meant Phenom II X2 555BE, fixed my original post.

I see on newegg, that the AMD Phenom II X4 945 Deneb 3.0GHz is listed at 95W TDP, so does that imply that if I'm able to unlock two more cores, I can stay within the motherboards limits by bumping the clock speed down to 3.0Ghz? Or am I being too simplistic?

That's a little too simplistic. Processors are not only binned based on whether or not they exhibit errors with certain cores enabled or at certain frequencies. They also have to hit the TDP target, which generally means that they must work at or below a given voltage in a given core/frequency config.

Thus, your 555 will not necessarily fall within the 95W power envelope with all 4 cores enabled at 3.0GHz, but you could always get lucky with a good chip.

 

[jaydee]

So what happens if it exceeds 95W? Unstable? Won't get past the BIOS?

 

[fffblackmage]

I think you'll be able to POST and get to the desktop. You don't max out TDP until you load all the cores 100%. Once that happens, I'm guessing you'll get a BSOD.

More importantly, I'm wondering if the mobo could suffer any damage trying to provide more than 95W. I don't think it should as there should be some sort of protection, but I don't know anything about it. Just merely guessing.

 

[Arsynic]

There's no guarantee that the last two cores are actually functional. They bin processors for a reason. Most likely you have a defective 4 core processor where AMD disabled the two bad cores and binned it as a dual core rather than throwing the whole thing away.

 

[Rifter]

you could solve this problem by going with a 95w quad from the start and not overclocking it, you know that right?

 

[mfenn]

So what happens if it exceeds 95W? Unstable? Won't get past the BIOS?

Like blackmage said, you'll probably see instability at load. If the mobo's power distribution is really cheap (and let's face it, it is 95W max), you could potentially burn it out.

 

[VirtualLarry]

What about those 45W quad-cores? Athlon II X4 something-e or something like that.

 

[0roo0roo]

power scales poorly on amd. i remember when i was comparing x3 vs x4, they practically used the same amount of power

 

[jaydee]

you could solve this problem by going with a 95w quad from the start and not overclocking it, you know that right?

Right, but like I said, my most intensive program initially is only single-threaded (and I'm on a budget), so it would be a better value to have a 3.2Ghz Phenom II X2 for $88 (and further overclock the dual cores a little bit), than slower quad cores that will be more expensive. I'm asking about the unlocking of cores, in case I decide to video edit, game or heavily multitask in the future, but it's clearly secondary concern.

There's no guarantee that the last two cores are actually functional. They bin processors for a reason. Most likely you have a defective 4 core processor where AMD disabled the two bad cores and binned it as a dual core rather than throwing the whole thing away.

I do realize that not all CPU's unlock, but reading around web, it seems highly likely that I can get at least one more core, and fairly likely that I can unlock both. But if it doesn't happen, not a big deal.

 

[jaydee]

Like blackmage said, you'll probably see instability at load. If the mobo's power distribution is really cheap (and let's face it, it is 95W max), you could potentially burn it out.

Gotcha. The motherboard is Asus though, and it has "Core Unlocker" and "Turbo Key II", so I would think it would have burnout protection.

 

[crucibelle]

You could get a non-black edition.. that will probably keep you at 95W if you unlock 2 more cores. I know the non-black editions don't OC as well, but better safe than sorry, IMO.

 

[fffblackmage]

power scales poorly on amd. i remember when i was comparing x3 vs x4, they practically used the same amount of power

I actually tried measuring my computer's power consumption with a Kill-a-Watt meter, comparing my 550BE as a dual core and as an unlocked quad core. I can't remember what I got for power consumption under load, but idle power consumption didn't change. I was hoping to see some power savings running the cpu as a dual core...

You could get a non-black edition.. that will probably keep you at 95W if you unlock 2 more cores. I know the non-black editions don't OC as well, but better safe than sorry, IMO.

BE has nothing to do with the TDP. BE only indicates that the CPU has an unlocked multiplier.

 

[crucibelle]

BE has nothing to do with the TDP. BE only indicates that the CPU has an unlocked multiplier.

Oooh, ok... I think I might be misunderstanding what TDP really is, then. I thought the 'black edition' processors had a higher TDP than the non BE's. For example, the BE Phenom II X4's I see are 125W, while the regular ones are 95W. I'm definitely screwing something up in my head.. lol! Thanks for the info.

 

[mfenn]

Oooh, ok... I think I might be misunderstanding what TDP really is, then. I thought the 'black edition' processors had a higher TDP than the non BE's. For example, the BE Phenom II X4's I see are 125W, while the regular ones are 95W. I'm definitely screwing something up in my head.. lol! Thanks for the info.

The higher TDP is because the BEs are clocked higher, not because they are BEs. The two happen to be correlated in this case, but one doesn't necessarily imply the other.