Wattage difference in cpu

[Planemech]

Hi,

Can someone explain why there are two different wattages for the same cpu? I am talking about in specifics of the Q8400 and Q8400s Yorkfield. Q8400 has 95w and the Q8400s has 65w. Is one better than the other?

Thanks

[MrFancypants]

The production method influences power consumption. More modern CPUs are smaller and can be operated with less voltage.

Less wattage means a smaller eletricity bill and less heat generation, so they would be better in most cases.

[Mr. Pedantic]

Not for those ones, no. Both run at the same speed. It's just that the 8400s gets the lower power consumption by having a lower voltage.

What happens when these CPUs are made is that every single one is subtly different. Some can run faster than others, some can run at a given speed cooler than others, and some can run at lower voltages while being stable at the same speeds. The chips that can do this are binned to produce CPUs like the Q8400s. While it's likely that you could make most normal Q8400 chips run at lower voltage than the Q8400s (this is known as undervolting) the Q8400s is guaranteed that speed and voltage out of the box, and will likely be able to go even lower.

So no, apart from the TDP, both chips are exactly the same. However, the new Core i5 750s does not do the same. For some reason Intel decided not to produce the 750s out of low voltage parts, but out of slower ones. The normal 750 runs at 2.66GHz, but the 750s runs at 2.4GHz. Just something to be aware of. I don't know if this is going to be a trend, but I hope not.

[C38368]

Originally Posted by Mr. Pedantic

So no, apart from the TDP, both chips are exactly the same. However, the new Core i5 750s does not do the same. For some reason Intel decided not to produce the 750s out of low voltage parts, but out of slower ones. The normal 750 runs at 2.66GHz, but the 750s runs at 2.4GHz. Just something to be aware of. I don't know if this is going to be a trend, but I hope not.

This could be the face of things to come, and if it is then I suspect that it is due to the architectural changes Intel made from Core to Nehalem. Or, it could be that Nehalem is not as mature as Core. Remember that, as processes improve and the fab becomes "better" at producing cores, superior parts will start coming out. This allows better speed binning (up) or volt binning (down). With a new technology or architecture, with many kinks to work out still, it's more cost-effective to bin low-yield parts and sell them as a lower-spec piece.

So the "low voltage" Nahalem parts will probably get a speed boost and TDP drop sometime in the coming year, as the architecture is refined.

Also remember that a CPU isn't going to run flat-out at it's TDP, even under normal max usage. This is one reason why TAT and Orthos are used to check cooling solutions and stability: they're far more stressful than real-world usage scenarios are going to be. An 85W part will consume less power than a 95W part, but neither will consume their full TDP and the average delta will be less than the max delta.

To answer the OP's question, probably not much difference. One part is just more efficient than the other. Time was it was a crap shoot for the buyer as to whether or not their CPU would be or not. Then Intel and AMD figured that they could make more money by making minor packaging changes and selling chips accordingly (they're binned regardless).

[Red_Fist]

My take on it, first you make a chip, works fine.

Then they added crap to adjust for "green" energy saving BS so it self regulates.

The amount of voltage is not a big deal,what you want is speed, all you need is .6 volts to turn a transistor.
But if you look at the formula E*I=P or, voltage times amps equals power.

Wattage is a measure of power derived from horsepower, something like 750 watts per hour = 1 horsepower
(might be wrong)

The higher voltages, the supply offers less current, lower voltages draw more current (power output try and stay the same).

But I think they just added power saving features, I could imagine if you ran it full blast it would be as hot as the other.

Also if they wanted to get chips to work at really low voltages, we need something other than "silicon" that could be turned on at .3 volts or less.The problem with that is they have reverse leaking and won't turn off enough.

[Mr. Pedantic]

Wattage is a measure of power derived from horsepower, something like 750 watts per hour = 1 horsepower
(might be wrong)

You are wrong. 1 joule is the amount of energy required to exert a force of 1 Newton over 1 meter. 1 watt is the use af 1 joule per second. It has nothing to do with horses.

[Red_Fist]

Originally Posted by Mr. Pedantic

You are wrong. 1 joule is the amount of energy required to exert a force of 1 Newton over 1 meter. 1 watt is the use af 1 joule per second. It has nothing to do with horses.

"one watt is the rate at which work is done when one ampere (A) of current flows through an electrical potential difference of one volt (V). "

(which would be a 1 ohm non-inductive or nonreactive load, like a carbon resistor).It will change that power to an X amount of heat).That amount of heat is the work one can relate to in real world applications.

If you notice the joule is a quantity of energy, a watt is a measure of power equivalent to the amount of "WORK" one can obtain compared to something we know how much work,(like horses) can do.

[Mr. Pedantic]

That is the definition of the volt, not the joule or the watt.

[C38368]

A watt is a derived unit of power that measures the rate of energy conversion. It is the product of voltage (potential) and amperage (current). One watt is equal to one joule per second.

Horsepower and watts have nothing in common, but for the fact that they measure the same thing (rate of energy conversion). Depending on the definition, one horsepower can be equivalent to anywhere from 735.5 to 9809.5W.

Because no energy is lost to friction with electronic devices, the 95W part at full tilt will draw and generate 95W of heat; the 65W part will draw and generate 65W of heat.

[general_kerr]

No, Not All Processors Are Created Equal.

Spoiler:

It's just a matter on minute manufacturing defects that determine things like wattage, Stable Frequency, et-cetera. More Expensive Processors will have less of these defects, letting them run at higher frequencies without crashing.