Proper i5 vs i7 power consumption test

[mikemex]

Hey folks.

If you think the FrankenPad days are over, you're mistaken! Just like I did years ago with my T61 (I built it from pieces since Lenovo never offered the combination of T8300, SXGA+ and integrated graphics) I decided I wanted a nice machine Lenovo doesn't offer. Or, at least, it never offered here in Mexico.

Long history short, I purchased an X1 Carbon Gen 9 with Spanish keyboard and WWAN (features I like) but with 1145G7 and 16GB of RAM (features I don't like). Honestly, I could live with the 1145G7 but 16GB of RAM felt quite limiting. I decided long time ago that 32GB was the minimum for a new computer.

At first, my plan was to buy a new motherboard and swap it, but motherboard prices are incredibly high, specially for the high end versions. So much that I ended up purchasing a complete donor machine for about the same price. I also reasoned that it would be much easier for me to sell an entire laptop than the motherboard alone, and recover most of my cost doing so.

I did the swap and now I've got a fully featured machine: 1185G7, 32GB of RAM, 1TB P31, low power 400 nit WUXGA screen, IR camera, WWAN, Spanish keyboard... the only features I lack are the ones I don't need, such as a touch screen.

The reason I'm writing this is because I had the rare opportunity to test two different processors with exactly the same hardware (because it's a direct swap). So I did some power consumption test with the old motherboard and the new, and I found something I already knew, but still interesting: despite common sense, the i7 is more power efficient than the i5.

The test consisted on continuous playback of a video with minimum brightness and sound off. I let it stabilize for a while with HWINFO monitoring it. With their respective / original machines, the i5 seemed to consume less: 5.3 vs 5.8 watt. But after swapping the motherboard, the i7 reached the same 5.3 watt base power figure. Though, to be fair, it seems to take it a bit longer to reach that figure.

Thing is, we're still comparing a 16GB motherboard with a 32GB one. The extra 16GB sure consumes a bit, so the i7 must be actually more efficient. And I confirmed it because the System Agent wattage for the I7 is lower than with the i5. I don't know why or what it means.

All I can say is that the lowest idle consumption I've seen on this machine was 1.37w which seems to be the most power-efficient generation ever released by intel to date. Sounds too good to be true, but it is: I spent a whole 4 minutes watching the battery charge drop by 0.1 watt, which means that it lasts 40 minutes per watt (57 watt battery x 40 minutes per watt = 2280 minutes, which is 38 hours. 57 watt / 38 hours = 1.5 watt).

Conclusion: the reason the i7 seems to consume more is that it is allowed to consume more. It's how it is configured what determines it. Properly configured (I run ThrottleStop on all my machines) the i7 is not only faster, but easier on power.

P. S. For those curious, the 0.5 watt difference was mostly in the screen (500 nit "Privacy Guard" on the donor machine, which is truly brighter even on the lowest setting).

[axur-delmeria]

The sample size is too small to make a generalized conclusion. In other words, your conclusions are valid for the two X1C G9 system boards you have, but probably not for every X1C G9 out there. Other than that, good work with the test.

[mikemex]

The sample size is too small to make a generalized conclusion. In other words, your conclusions are valid for the two X1C G9 system boards you have, but probably not for every X1C G9 out there.

Yeah, you could say that. But truth is, there is nothing mysterious here: processors have always been tested during manufacturing and the best performing ones are sold as high end models to increase revenue. In the semiconductor industry power is everything: if a chip can work at a higher frequency, it is because it's more power efficient. Sometimes intel might "undercut" some i7 grade chips and sell them as i5 to meet demands, but an i7 is always a high end part. That's why it nominally has higher amounts of cores and cache: fabs disable defective parts of a chip to salvage them from scrap / increase production yields. Lower end models are a way to make room for that.

Any way you look at it, there is some (small) margin between an i5 grade chip and an i7 grade one. You can use it to increase performance, like intel usually does, or to reduce power consumption, like do.