Quad Core Energy Use

[stryder256]

I know that Quad core will use more energy when under heavy load, but I'm wondering when the system is under normal use (using Firefox, for instance), will there be a way to idle the extra two cores in order to save on energy usage? Or is that impossible given the design?

Also, does anyone know how much hotter it will run than the Dual Cores?

 

[QuixoticOne]

If you make use of the features that are already built into the CPU (EIST = Speed Step),
and the BIOS (ACPI = enabled), and the OS (enabling Speed Step, power conservation, etc.),
it will do a reasonably good job at using less power when the system is idle.

The CPU will switch to running at less than half speed when it is idle, the CPU voltage will lower automatically to save power at the lower frequency, and software instructions executed will see that major power consuming actions of the CPU and RAM and chipset will be turned off effectively.

You didn't specify the CPU model, but here's an example with the new generation
QX9650 CPU; because it is the brand new 45nm design it probably uses much LESS
power than most any previous dual core or quad core CPU models.
http://www.anandtech.com/cpuch...howdoc.aspx?i=3184&p=2
http://www.anandtech.com/cpuch...howdoc.aspx?i=3184&p=3

As you can see the power due to the CPU is down around 8W-10W when the system is idle at a configured 2.4GHz maximum operating frequency. The measured power consumption goes up to around 36W under load at the same frequency.

As you can also see, the loaded power consumption increases pretty linearly with frequency increases as you overclock the part between 2 GHz up to 3GHz+.

Most of the older generation of Core2 Dual and Core2 Quad CPUs have maximum allowable power consumptions of between 65W for a few of the dual core chips and 110W or so for the quad core versions.

Typical real world power consumption of these processors under heavy load at stock operating speed / voltage is usually a decent bit less than the maximum TDP figure the part is rated for by Intel.

You can look at the Intel rated Thermal Design Power here for any given stepping of any given CPU they make, and keep in mind that the usual actual figure used under load without overclocking very much will be maybe 75% of that number:
http://processorfinder.intel.com/Default.aspx

Originally posted by: stryder256
I know that Quad core will use more energy when under heavy load, but I'm wondering when the system is under normal use (using Firefox, for instance), will there be a way to idle the extra two cores in order to save on energy usage? Or is that impossible given the design?

Also, does anyone know how much hotter it will run than the Dual Cores?

 

[QuixoticOne]

Here are some actual system power consumption figures for the older
generation of Dual Core CPUs:
http://www.anandtech.com/cpuch...howdoc.aspx?i=2903&p=7

Here's the idle and load power data for a system with a Q6600 older
generation quad core CPU:
http://www.anandtech.com/cpuch...howdoc.aspx?i=3066&p=2

If you're concerned about heat / power consumption savings, I'd certainly look at getting one of the newer 45nm generation CPUs either a dual or quad core model, e.g. Q9300, Q9450, E8400, or others higher or lower in those numbering series. They have the lowest idle power consumptions of powerful desktop CPUs relative to the past models of the duals/quads.

AMD CPUs often do have better oferall idle and load power consumptions than Intels, though sometimes the actual compute performance is less on the AMD and Intel so depending on what you're doing you may find reason to trade off power consumption for compute power.

If you really just want basic computing that works at the lowest possible power consumption, look at the "mobile" family CPUs as well as dedicated platforms like the Mini-ITX platform with processors like VIA's; often times the whole motherboard+CPU+RAM of a Mini-ITX system can have a power consumption of only 5W - 15W under *LOAD*, and that reduces to under 2W when moderately idle. Of course the maximum compute performance is much less than one would get in a dual or quad core desktop PC, but it's enough for virtually all basic applications just not high performance games.
http://www.idotpc.com/TheStore...ories.asp?idCategory=2

 

[stryder256]

That was a fantastic post, Quixotic. Thank you

 

[lopri]

I have moved the thread from Motherboard Forum to the CPU & Overclocking Forum.