Why is Ivy Bridge system idle power consumption so much lower on mobile vs desktop?

[Fjodor2001]

Hi,

An Ivy Bridge based laptop (or Ultrabook) can have a system idle power consumption as low as 5 W (not counting the display power consumption). However a corresponding desktop Ivy Bridge system will have a system idle power consumption of around 30 W.

So how come there's such a huge difference in idle power consumption, even if both computer have about the same hardware (SSD, RAM, and only use IGP)?

Does anyone have a clue where the extra 25 W are wasted on the desktop computer?

 

[dma0991]

The motherboard alone should be accounted for the 25W difference.

 

[blastingcap]

Motherboards with more power phases and more and more capable connections, ranging from SATA-6 to many more USB 2/3 connectors, PCIe etc. You can actually save a bit of idle power simply by disabling some of those controllers and ports if you don't need them.

For more info: http://www.bit-tech.net/hardware/pcs/2010/02/24/energy-efficient-hardware-investigated/4

 

[LOL_Wut_Axel]

Apart from the motherboards there's also the CPU itself. On idle, a mobile Ivy Bridge CPU will run at 800MHz, and a desktop model will run at 1600MHz. Consequently, the voltage will be lower as well. All of these things mean much lower power consumption.

Using my Kill-a-Watt my SB-equipped laptop is measured at 8W on idle. My desktop, 70W.

 

[Lonyo]

Actually you can get a desktop down to 20w or so without much effort.
That's still significantly more than a laptop, but as mentioned above, a laptop doesn't have a lot of the things a desktop does. When you're talking about 15w, even fans start to play a big part, we're talking maybe 2w more for fans on a desktop vs laptop, even if they are on low speed mode.
Strip out the motherboard, add a more power optimised chipset (lower voltage etc), go for the CPU with the best power characteristics etc, and that last 15w is something the end user can't achieve, but Intel/AMD can.

 

[Puppies04]

I agree with the other comments in this thread, also laptop HDDs tend to have much more agressive power saving features than their desktop couterparts. Be aware if you are comparing a desktop I7 or I5 to a laptop one you may not be on a level playing field. The criteria for the I5 or I7 name changes quite dramatically depending on which platform it is designed.

 

[BonzaiDuck]

I agree with the other comments in this thread, also laptop HDDs tend to have much more agressive power saving features than their desktop couterparts. Be aware if you are comparing a desktop I7 or I5 to a laptop one you may not be on a level playing field. The criteria for the I5 or I7 name changes quite dramatically depending on which platform it is designed.

I have an idea what good SSD power-consumption can be. Not familiar enough with the conventional 2.5" laptop drive. At one time, I contemplated building a RAIDed set with some -- but didn't.

I have to buy a laptop sooner or later. I could boast about how I might have built an early laptop prototype back when the Osborne 1 was released. Some might laugh, but I can stand proud while laughing at myself.

I've put off buying a laptop, since I don't travel much anymore. Probably, I'd like a tablet or I-pad to take to the grocery, but that, too, could be overkill. I'm "plotting an optimal acquisition" . . . .

 

[Ken g6]

Another reason could be the power supplies. Power supplies generally aren't efficient under 20% of their rated wattage. Generally, a desktop PSU will be 300W or more, while a laptop may be 60W or less.

 

[AtenRa]

Some Ultrabooks only have a single DIMM memory, that could save 5-10Watts over a dual memory DIMM configuration.

 

[ShintaiDK]

Some Ultrabooks only have a single DIMM memory, that could save 5-10Watts over a dual memory DIMM configuration.

1 DIMM doesnt save that much at all. Not even close.

 

[hans007]

unplug every fan in your desktop.

get a solid state power supply like a pico psu 120 (which is 97% efficient like a laptop psu). even a 80plus psu is probably only like 80% efficient at a lower power state like idle. i dont think it even has to be 80% to be 80 bronze.

so 17% differential at say 20W is another nearly 2W

and itll probably cut it down a lot.

the motherboard electronics and things like fans use some power. i mean a fan that uses say .15 amps at 12v is still like over 2W.

 

[coffeejunkee]

The motherboard alone should be accounted for the 25W difference.

This.

Another reason could be the power supplies. Power supplies generally aren't efficient under 20% of their rated wattage. Generally, a desktop PSU will be 300W or more, while a laptop may be 60W or less.

And this.

Apart from the motherboards there's also the CPU itself. On idle, a mobile Ivy Bridge CPU will run at 800MHz, and a desktop model will run at 1600MHz. Consequently, the voltage will be lower as well. All of these things mean much lower power consumption.

Using my Kill-a-Watt my SB-equipped laptop is measured at 8W on idle. My desktop, 70W.

Not sure about this, desktop cpu's almost completely turn themselves off due to c-states.

A guy on a Dutch forum has modded his pc so it uses only 8.5W idle. Proof: http://ssj3gohan.tweakblogs.net/blog/6081/10w-i3-systeem-nu-voor-maar-85w!-1.html. English summary of the project: http://ssj3gohan.tweakblogs.net/blog/6112/85w-core-i3-based-desktop-computer-(english).html. Basically desktop motherboards could be much more power efficient if manufacturers weren't so lazy/cost conscious.

 

[Lonyo]

This.



And this.



Not sure about this, desktop cpu's almost completely turn themselves off due to c-states.

A guy on a Dutch forum has modded his pc so it uses only 8.5W idle. Proof: http://ssj3gohan.tweakblogs.net/blog/6081/10w-i3-systeem-nu-voor-maar-85w!-1.html. English summary of the project: http://ssj3gohan.tweakblogs.net/blog/6112/85w-core-i3-based-desktop-computer-(english).html. Basically desktop motherboards could be much more power efficient if manufacturers weren't so lazy/cost conscious.

They would also end up being more expensive, so it's not just about the manufacturers being cost conscious. Most end users don't care enough about power use to pay the premium required for a lower power motherboard.

 

[AtenRa]

1 DIMM doesnt save that much at all. Not even close.

Core i7 920 @ 3.8GHz
Noctua NH-14 (dual Fan)
ASUS Rampage II Gene
ASUS HD6950 1GB at 881MHz
3x 4GB Kingston 1333MHz @ 1451MHz 1.65v
Intel 320 120GB SSD
SeaGate 2TB SATA-3
SONY BluRay
3x 120mm system fans
Enermax Revolution 850W 80+

3x DIMMs = 132W idle
2x DIMMs = 129W idle
1x DIMMs = 127W idle

Its not 10 watts but depending on the platform and your memory (frequency, voltage) you can see 2 to 5 Watts difference from a single to dual DIMM configuration in idle.

 

[Yuriman]

^ That's why I opted for 1.25v DDR3 1600. It adds up.

 

[Lonbjerg]

For the same reason as the performance is lower om mobile compared to desktop...quite logical, eh?

 

[Fjodor2001]

For the same reason as the performance is lower om mobile compared to desktop...quite logical, eh?

Can someone please hand over the Nobel prize to this genius right away?

 

[jacktesterson]

Can someone please hand over the Nobel prize to this genius right away?

Exactly

That gap is also closer than ever before. The i7's are in stock 2500k performance range now, not too shabby for a notebook.