TDP 25W vs 35W: Energy Savings

Hi,

Just wondering about the energy benefit of a more efficient processor such as P8800 vs T9550. Has anyone gone from a 35W to 25W processor to find the battery life last alot longer, or is it only like afew minutes longer. Just wondering, because I'm trying to decide on the payoff between more power and battery life.

Thanks!

 

If you're running your machine at full load on battery... you'll probably see a significant difference in battery life. If you're usually just idling on battery... it won't be much of a difference. If you undervolt both processors, you can probably narrow the difference even more, especially at load.

 

Battery life won't really benefit from the lower TDP all that much (well, it WILL, however nothing to really concern yourself over with).
It's the heat output that's lower here which also translates to lower power consumption and longer lifespan of your parts.

However, if you are that worried over the battery life in contrast to the lower power consumption ratio ... then simply undervolt the CPU and be done with it.

 

If u undervolt the 35W processor , battery life will increase and energy consumption should be the same as 25W one... don't worry about this , these are just intel gimmicks... no real difference in between both of them in real life when someone tested this out.

 

If its just 25W versus 35W within the same processor family (and same manufacturing process), then there is absolutely no energy savings to buying the 35W processor versus the 25W, or vice versa, for the same load.

Now, if you can replace a 45nm processor that dissipates 35W, with a 32nm processor that dissipates 25W, then typically, you would have some savings there. If you can cut 5W off your average load, on, say, an 85Wh battery that normally lasts 4 hours -- then you potentially could get another hour out of the system.

Generally speaking, changing CPU's on laptops is a bad idea though...

 

Yes there is. Have you noticed reviews of laptops with 10+ hour idle or super long time like that and it plummets to 3-4 with usage? Well that "3-4 hour" will increase with lower TDP CPUs. Difference between "Claimed battery life" and "Actual battery life" mostly depend on higher end numbers like TDP.

And TDP is more important than you think. As you start using the laptop and install programs, actual usage power will get fairly close to TDP values.

 

Go for the cheapest , maybe a 5watt tdp difference under full cpu load , see spec comparison below.

http://ark.intel.com/Compare.aspx?ids=37130,40380,

 

Why is it a bad idea? The way I see it, it can be a good idea if you are unable to overclock, and you want better performance in CPU heavy tasks.

 

Or, put more simply, TDP is NOT a direct measure of power consumption.

TDP is an accurate measure of heat dissipation. In some, not all, cases, it is an indication of power consumption but not a wholly accurate one.

You need to dig out the real power consumption numbers for your CPUs to get an accurate comparison.

 

Hi guys, thanks for all the useful posts. I think to summarize it seems that given all things equal (clock speed, FSB, cache) I should just go with the cheaper of the two (25W vs 35W). Atleast this is what I am leaning towards.

I am also in a quandry why changing the processor is a bad idea. I have an SR series (which looks relatively easy to swap) and doesn't "the man" just do the same thing when you're looking at the same series of laptop which have different CPU options? I realize that the motherboards can be different but I don't think that is the case here.

Anyways, thanks again!

 

ScKaSx, go with a 35W chip. They are going to be exactly the same in terms of power efficiency as a 25W chip. Why is that, well Intel is wise when it comes to advertising, and marketing.
Intel does not test every single processor which they manufacture. They will make thousands of the same processor. Out of that bin, 1 is tested. If that chip is found to be 24.99Watts TDP, the entire bin is marked as a 25Watt CPU. If the chip is tested and found to be 25.01Watts TDP, the entire bin is marked as 35 Watts TDP.
Why does Intel do this, well it is simple.
Charge suckers more for the same exact good, and get away with it. They can market all they want, but it is fact that the 25 watt TDP chips do not yield lower temperatures or more battery life than the 35 watt TDP chips. You can believe those who fall for the advertisment gimmicks, or you can believe the truth, it is up to you.

K-TRON

 

K-Tron u put it accross just like i wanted to! Excellent explanation!