Power consumption can be an interesting topic when you're building a home server system that runs 24/7. To estimate the maximum power consumption of your CPU you can look at the Thermal Design Power or TDP values that are provided by the CPU manufacturer. Common values include 45W, 65W and 95W.
TDP not a magic bullet
However, TDP itself won't tell you how much power the chip consumes; it's a thermal specification to describe what amount of heat the casing/environment would need to be able to dissipate, in order for it not to overheat (stay below Tmax value).
Also, TDP does not even accurately predict maximum power consumption; three chips clocked slightly different of eachother but belonging to the same family might all three share the same TDP, but still the higher clocked version will consume more power when fully stressed.
Idle power consumption is what you should look for!
Instead of looking for TDP or maximum power consumption, for a 24/7 server what you actually want is a very low idle power consumption. Idle means when you're not really doing anything, which is where all the modern power saving technologies come into play!
Advanced power saving
Modern CPUs of both AMD / Intel are very low idle power. Intel has the best manufacturing process, able to sell 32nm High-K Metal Gate CPUs that have very low leakage and thus low idle power consumption, even when turning some power saving techniques completely off. AMD relies heavily on its Cool'N'Quiet technique, which both throttles clock frequency and voltage, but is very successful at reducing idle power consumption as well; as long as this power saving technique is activated in both BIOS and Operating System.
What to look for?
The result of all this power saving is that a six-core AMD chip uses less idle power consumption than an older AMD Sempron, with much less sophisticated power saving and older production process. Most modern CPUs of both AMD (45nm) and Intel (32nm) would be a good choice. The AMD Phenom with its higher caches would consume a bit more than the Athlons, but it's not much. Any modern CPU should be <10W at idle.
Platform power
With CPU power kept at a low, the platform power is up next. This includes the motherboard, memory, chipset, graphics, network, controllers, etc. The more modern platform generally the lower/better the idle power consumption.
An interesting note here is the earlier Atom platforms, where the CPU consumed only a couple watts, while the chipset did more than 10 times that amount, so these platforms actually consume more idle power than recent AMD six-core systems are capable of! Same story for Intel 32nm and efficient chipsets; though Intel platform has more power consuming chipsets at the moment.
What's up next?
In the not-too-distant horizon we can see interesting storage platforms based on AMD Zacate platform (the AMD competition to Intel Atom) and Intel Sandy Bridge architecture, which adds significant performance gains and like AMD Fusion, combines CPU and GPU in one die/package.
If you're looking for a low idle power system, the AMD Zacate platform should be very interesting to you. Platform power is as low as 9 Watts as measured on a beta-board thus far. This sounds very promising and would both pack reasonable performance, high performance I/O with very low idle power. You would be able to get a 1.2GHz dualcore or 1.6GHz dualcore with gigabit ethernet, PCI-express 2.0 x16 and 6x SATA/6Gbps at your disposal; all this for a few watts? It almost sounds unbelievable!
Feel free to share your thoughts.
TDP not a magic bullet
However, TDP itself won't tell you how much power the chip consumes; it's a thermal specification to describe what amount of heat the casing/environment would need to be able to dissipate, in order for it not to overheat (stay below Tmax value).
Also, TDP does not even accurately predict maximum power consumption; three chips clocked slightly different of eachother but belonging to the same family might all three share the same TDP, but still the higher clocked version will consume more power when fully stressed.
Idle power consumption is what you should look for!
Instead of looking for TDP or maximum power consumption, for a 24/7 server what you actually want is a very low idle power consumption. Idle means when you're not really doing anything, which is where all the modern power saving technologies come into play!
Advanced power saving
Modern CPUs of both AMD / Intel are very low idle power. Intel has the best manufacturing process, able to sell 32nm High-K Metal Gate CPUs that have very low leakage and thus low idle power consumption, even when turning some power saving techniques completely off. AMD relies heavily on its Cool'N'Quiet technique, which both throttles clock frequency and voltage, but is very successful at reducing idle power consumption as well; as long as this power saving technique is activated in both BIOS and Operating System.
What to look for?
The result of all this power saving is that a six-core AMD chip uses less idle power consumption than an older AMD Sempron, with much less sophisticated power saving and older production process. Most modern CPUs of both AMD (45nm) and Intel (32nm) would be a good choice. The AMD Phenom with its higher caches would consume a bit more than the Athlons, but it's not much. Any modern CPU should be <10W at idle.
Platform power
With CPU power kept at a low, the platform power is up next. This includes the motherboard, memory, chipset, graphics, network, controllers, etc. The more modern platform generally the lower/better the idle power consumption.
An interesting note here is the earlier Atom platforms, where the CPU consumed only a couple watts, while the chipset did more than 10 times that amount, so these platforms actually consume more idle power than recent AMD six-core systems are capable of! Same story for Intel 32nm and efficient chipsets; though Intel platform has more power consuming chipsets at the moment.
What's up next?
In the not-too-distant horizon we can see interesting storage platforms based on AMD Zacate platform (the AMD competition to Intel Atom) and Intel Sandy Bridge architecture, which adds significant performance gains and like AMD Fusion, combines CPU and GPU in one die/package.
If you're looking for a low idle power system, the AMD Zacate platform should be very interesting to you. Platform power is as low as 9 Watts as measured on a beta-board thus far. This sounds very promising and would both pack reasonable performance, high performance I/O with very low idle power. You would be able to get a 1.2GHz dualcore or 1.6GHz dualcore with gigabit ethernet, PCI-express 2.0 x16 and 6x SATA/6Gbps at your disposal; all this for a few watts? It almost sounds unbelievable!
Feel free to share your thoughts.
