"Paul" <(E-Mail Removed)> wrote in message
news:itrufo$f5a$(E-Mail Removed)...
> GT wrote:
>> CPU TDP question:
>> Why are the e6300, e6400 and e6600 all rated at 65w TDP? As I understand
>> it, the heat output is based on the CPU architecture multiplied by the
>> CPU clock speed and CPU vCore squared (roughly). With these 3 chips (and
>> other CPU families) the only different is their speed (and cache levels),
>> so the heat should be lowest in the 6300, middle in the 6400 and top in
>> the 6600?
>>
>> I expect that the TDP is just a max rating to enable users to select the
>> correct cooler and the slower chips in reality produce less heat than the
>> faster ones, but can someone confirm this?
>>
>> In short, if I take an e6400 and overclock it from its stock 2.16GHz up
>> to the 2.4GHz stock speed of the e6600, then would the heat output match
>> that of a stock e6600?
>
> CPUs are plopped into "bins", for the purposes of the TDP number.
> Everything in the same bin, might benefit from the same retail cooler.
>
> Say I was looking in the Intel catalog, and saw this.
>
> 2.1GHz TDP=65W
> 2.2GHz TDP=65W
> 2.3GHz TDP=65W
>
> 2.4GHz TDP=89W
> 2.5GHz TDP=89W
>
> What that would tell me, is the one just before the transition,
> is nearest to being really representative. So the 2.3GHz has a real
> TDP rating of 65W, while the slower ones don't actually get that hot.
>
> The 2.4GHz one is in the next set of bins, and draws much less than
> 89W. It could be drawing 65W or a little more. But guessing at it,
> really doesn't tell us what is going on. Measurements are more
> illuminating.
>
> When they include a heatsink fan in the retail CPU box, the first
> three will come with the same cooler. The last two, will have a
> slightly beefier cooler.
>
> The accuracy and intent of TDP has changed over the years.
> On my Northwood processors, the actual power might be very close
> to the TDP. Maybe even a couple watts above it.
>
> My Core2 processors are on the low side. I think my 3GHz Core2
> 65W, might have measured 45W. Another Core2 I've got, measures
> 36W or so. And that is measured on the ATX12V cable, so the real
> power as measured at the socket itself, is lower. (Vcore emits
> some heat, and isn't 100% efficient.) Those measurements are
> done with something like Prime95 running.
>
> For small overclocks, it is probably sufficient to use a simple
> ratio, or other rule, and assume nothing is going to burn up.
>
> If you wanted a more accurate method, you'd
>
> 1) Measure the stock consumption like I did.
>
> 2) Use FCV**2 equation, to estimate the new power rating.
>
> Frequency scaling is directly proportional. Taking the
> ratio of your two frequencies, I get 1.11x, which means
> 11 percent more power due to frequency.
>
> The voltage term is V_squared. If the original Vcore was
> 1.3V and to keep the processor stable, you needed 1.35V,
> then take the ratio of 1.35/1.3 and square the result to
> get 1.078. That means 7.8% more power, comes from the
> extra voltage I used in the overclock.
>
> Taking both factors into account = 1.11 * 1.078 = 1.197
> or close to 20% more power.
>
> So if the original power was 40W, and you overclocked with
> a bit more Vcore (tested for stability and found it necessary),
> the estimated power would be 40W * 1.2 = 48W roughly. You could
> then clamp on the ammeter, and verify it.
>
> So then the next natural question would be, "is the retail
> heatsink/fan good enough for 48W ?". No data is available
> to answer that :-) You can't link the third party coolers Intel
> buys, to any data. No theta_R is available. We have to assume
> the cooler is "good enough" in some sense, but we don't know
> how good.
>
> Overclocking does have its limits. The most extreme I've heard
> of, is overclocking the D 805 to 4GHz. When the increased Vcore
> is taken into account, power consumption is around 200W. This
> exceeds the rating of the 2x2 power connector on the motherboard.
> And has caused foam plastic to melt, in the vicinity of the
> Vcore regulator. So there are a few overclocks of that nature,
> where it pays to keep your calculator handy. Smokin good fun...
>
> *******
>
> The story on the AMD side is even more puzzling. In that AMD
> announced some time ago, that it planned to cheat on power
> numbers. I don't remember the details, and I'm not
> interested in looking it up :-) That's the problem with TDP,
> is it is politically charged, and a marketing brownie point.
> Too much honesty, isn't good for business. Actual measurements
> are the only way to add realism to the picture.
>
> Paul
Thanks Paul. I was asking with a view to under-volting and possibly
under-clocking for a media centre PC. I have used the formula before to
calculate power/heat, but was just wondering about the TDP classification.
You have confirmed what I thought - the TDP is just a group thing for a
family of processors, the actualy power/heat varies based on vCore and
Frequency. Thanks.
