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I'm looking at getting an Asus P5G41T-M LX G41 motherboard. In the manual here, it states that a minimum of 400 watt PSU is recommended. My question is, what is this figure including as I can't quite see the motherboard alone requiring 400 watts?


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up vote 4 down vote accepted

Everything else that makes up the machine, obviously: the CPU, discrete graphics card (which can often use a lot, if fitted), RAM, disk drives, optical drives, PCIe cards, case fans, etc.

Also, the figure would be for full maximum load (plus some extra capacity over that), and not just what the computer will usually be using while idling.

There are quite a few online calculators which you could use to see how much each component roughly uses, like this one.

It would be wise to get a good quality PSU with a high efficiency and not to get one much more powerful than you need, as it would be a waste of money, and slightly less efficient. PSUs are generally most efficient at 40-70% load (roughly).

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Hello paradroid, thanks for the answer. It seems nonsensical for a motherboard manufacturer to recommend a power supply as they don't have a clue what components I'm going to be running. On the other hand I can't see anywhere where the motherboard states the power it requires? Thanks. – R4D4 Dec 18 '11 at 13:29
@R4D4: Well it is a minimum that was given, and what sort of CPU, RAM, number of graphics cards, etc is known. Also, most computers built using that motherboard or any other are similar. When enthusiasts build high-performance machines they would be expected to know about PSU ratings. – paradroid Dec 18 '11 at 16:27

That is just a general minimum rating needed for a maximum setup (all hard rives and peripherals installed) but it excludes the power ration for graphics cards, s o...

One thing to consider is not just the motherboard, but if you want to get a good graphics card-- that one alone needs 400Watt + 400Watt Motherboard .. So many gaming PC's use 850Watt power supplies. (you will notice when you buy a high end GFX card they suggest using 600/800/1000Watt and this is the max for everything used)

It does not meaning uses the 850Watts constantly, it is a switched power supply and is controlled via the motherboard and/or software of your operating system. That is why it is important to enable power saving features and install the correct drivers for your OS.

So when you are not doing anything it can use as little as 50Watts.

But when gaming it jumps up to 600-800watts.

One thing to keep in mind- do not buy the cheapest pwoer supplies- because they tend to blow out when you start using the near maximum rating. I have seen this happen dozens of times, and people come back later and buy a proper PSU(you can tell by comparing the weight of the same rated PSU) The better PSU's sue high quality capicitors and coil transformers and a bit more clever technology to decrease the chance of a blow out, they also usaully come with 3 to 5 years warranty, where as chinese el-cheepo only 1 year.

Usually when i am in doubt i use one of these wall power meters and monitor the usage.

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