JaconKin, on 10 August 2011 - 09:38 AM, said:
What do you mean, sort of answering basic questions like what is overclocking?, what is the difference between this RAM and That?, What is SLI and Xfire?, How big of a power supply do I need etc?.
Yes, like
Power Supplies
What do I need to know?
Brand and even individual model within a brand matters. There is no standard for how manufacturers rate the total wattage for their power supplies. So you can have two power supplies both labeled as 500W but actually deliver different real world power. Some power supplies can't even deliver the wattage they're rated for!
This different way of labeling a power supply comes from the different types of power the PSU delivers. PCs have required three different voltages to be supplied to them by the rails of PSU: 3.3V, 5V, and 12V. The power in watts is calculated by taking the voltage and multiplying it by the amperage the unit is rated for. For example a power supply says it can deliver 15A (amps) on the +3.3V rail, which would equal 49.5W for the +3.3V rail. The inconsistency comes with how these different rails and their wattage are added together. Some manufacturers are content to label the final wattage as the absolute maximum power delivered (which is a major strain on the componets of the PSU). Some manufacturers are more realistic and label the final wattage the PSU can deliver safely at all times, which in turn means some 500W power supplies can deliver 600W of real power without blowing up or shutting down.
Modern PCs need most of their power to come from the +12V rail. The video card and processor almost exclusively use the +12V rail, and they are the most power hungry components in a computer system. Bad power supplies will have the wattage of the 3.3V and 5V rails account for a lot of the final total output. Good power supplies will be able to deliver a lot on the +12V rails compared to the final total output since that is the most important rail. You'll also notice some power supplies have more than one +12V rail. Since most, if not all, multiple +12V rails power supplies "artificially" split up the +12V rails, you simply can't add the +12V1, +12V2, etc rails together to find out the maximum power the PSU can deliver on the +12V rail. You have to look at the combined +12V rail number which is usually listed somewhere on the label.
So pay attention to who makes the power supply. In general you can feel safe about buying a power supply made by these guys:
Seasonic, Antec, Corsair, Enermax, PC Power and Cooling, Silverstone, OCZ, XFX.
Price is also an indicator you can use. Up to 500W expect to pay $40-$60. 500W-750W expect to pay between $60-$120. Over 850W expect to pay $120 or more. So if you see an 850W PSU going for $75... stay away! It's probably junk.
All recent good power supplies are also being rated
80 Plus Certified. So that is another indicator of the quality of the power supply. Make sure you get one that is 80 Plus, Bronze, Silver, or Gold. So if you see an Antec power supply that is not rated 80 Plus, then good chances it's a very old design and you should avoid it.
So how much power do I need?
A quick way to figure this out is to use an
online PSU calculator. They will give you a rough estimation. Just keep in mind the figures they show assume a quality power supply. If you want to estimate yourself, then you will need to put some work into it. First you'll need to estimate how much power your system will draw and then you'll need to look at the power supply and what it can deliver on the +12V rails.
Since the video card and processor are the two biggest hogs, you need to find out what they actually need. To get real-world numbers for the video card, check out the latest review at
Techpowerup. They measure how much power the video card is drawing only. If you're going to be
gaming then you need to look at the
Peak graph. If you're going to do
GPGPU work like Folding@Home then you should look at the
Maximum graph. We'll use the GTX 460 as an example here, and it draws 130W while gaming. To get real world numbers for the processor, check the latest review at
Lost Circuits. They only test how much power the processor is using. We'll use the the 2500K as an example, and it uses 46W under load.
To account for the power to the rest of the system, use 50W as an estimation. So 130W + 46W + 50W = 226W. Now you do not want the power supply to be running at its maximum capacity, so add 25% to the total we just figured. 226W * 1.25 = 283W. If you divide 283W by 12V, you get 24A. You need to make sure the power supply is rated to deliver at least 24A on the +12V rail (or combined +12V rails). You can find out what the PSU can do by looking at the label on the power supply, as seen in
Example 1 and
Example 2. The first example states the max load for 12V1 and 12V2 is 384W, so this power supply is good enough for our example gaming system. The second example doesn't explicitly state the max load, but you'll notice it has 432W directly under +12V1 and +12V2 numbers, so that means 432W is what those two +12V rails can deliver combined.
Another way to get a rough estimation is to simply look at the TDP of the video card and processor. This is a safe estimate as TDP should be higher than what you'll normally see in the real world. You can get the TDP of the video card at
GPU Review under "
Max Power Draw" and the TDP of the processor at
CPU-World under "
Thermal Design Power (W)".
It doesn't hurt to have a power supply bigger than what you need. So play it safe if you're not comfortable or you're unsure and get a power supply more than you think you need. Power supplies will only output the wattage the system components require. It's like plugging your TV into your wall outlet. The TV doesn't blow up because it's only drawing the power it needs and not the maximum power your house circuit can provide.
What if I'm overclocking?
Overclocking throws off all the estimations. Overclocking raises the requirements on the power supply. Since you can overclock a little or a lot, how much more power you need depends on how far you are going to overclock. Changing the voltages plays a very signficant role and has the biggest impact. If you're overclocking the processor at stock voltages then add 40W to the base estimation. Likewise if you're overclocking the video card at stock voltages add another 40W. If you're increasing the voltage, you can easily add another 100W, or more, for
each the processor and video card, meaning an estimated additional 200W would be needed. So it's definitely recommended to estimate on the high side when picking out a power supply for an overclocked system.
What if I want to know more?
If you want to know more, check out some power supply reviews. These reviewers go in depth and examine all aspects of the power supply. You will learn a lot by reading their reviews and articles.
Hardware Secrets
Techpowerup
Jonny Guru