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GPU and CPU power connections

Is the connections we are making, bad for our devices?
A mistake like this can cost you a lot of money.
A GPU is a “Graphics Processing Unit”, it is located in the video card. A CPU is a “Central Processing Unit”, it is located on the main board. I, at one time had a lot of questions about there power connectors, their current rating, the cross compatibility, jumper wires and unorthodox looking configurations, and what adaptors are safe to use. I did a lot of research and found conflicting answers. I looked at how reputable the source was, and how often I saw other reputable sources give the same answer. Being an electrical technician with 35 years experience, I myself, have a good working knowledge of this subject. I pooled of this information into one easy to understand writing, then made an illustration to go with it. The purpose of this article is to save you a lot of research time, and turn you into an expert by giving you good reliable information.

The white smoke of death: As you can see by the plug illustrations in the middle of this guide, the 8 pin plug for the CPU power that plugs into the main board (ESP-12V) is completely incompatible with the PCIe graphics card’s power connection. Even though they are keyed differently; they do look very similar and it is possible to force a plug into the wrong receptacle. If you make the mistake of forcing the connection, when you apply power, you may see a white cloud form around the power supply and the graphics card or main board; the damage will be extensive. You will have permanently damaged several very expensive components that you will now need to replace. Power supply manufacturers normally mark these connectors with tags, never tear these tags off and never force the connection. If the connection is difficult to make, double check the plug keys. This is not the only mistake that you can make.

Understanding how the system is set up: In a power supply, there is only one circuit that generates 12 volt DC. Even if there are multiple rails, all 12 volt lines come from the same place. This is the same rule for the CPU and GPU inputs. All of the power comes from one point in the power supply, and goes into one point on each device. ** The way this system works is, many wires (around 16 gauge) are used, the wire system is easily customizable by adding multiple wires until the wattage availability exceeds the devices needs. ** The above rules also apply to ground. All ground connections are connected to earth ground, there is only one ground. Multiple connections only increase wattage availability. All grounds come from one point and go into one point on each device. There is one exception, grounds that go to sensor; sensor is a separate circuit within the device. ** There is no such thing as making too much wattage available, the device will only use what it needs; your only worry is not supplying enough wattage. Current starvation causes overheating, errors, and failures.

Y- Adaptors
The 6 and 8 pin adaptors and their power ratings: The 6 and 8 pin adaptors are called Y-adapters because they each have two 4 pin IDE Molex power receptacles. Sometimes they are supplied with the products that use them, and they are also readily available on the web. Each IDE Molex power plug (coming from the power supply) only has one 12 volt line. Each GPU and CPU adaptor's 12 volt line needs about 40 watts (3.3 amps) from the power supply; this is NOT standardized by PCI-SIG. For the graphics card power connectors, the 6 pin adaptor has two 12 volt lines, so it needs 80 watts (6.7 amps) , and the 8 pin adaptor has three 12 volt lines, so it requires 120 watts (10 amps). For the CPU power connectors, the 4 pin connector has two 12 volt lines, so it needs 80 watts (6.7 amps) , and the 8 pin adaptor has four 12 volt lines, so it requires 160 watts (13.3 amps) . If you are going to use any of these adaptors, you need to check the power supply and its power distribution to its rails and the available connectors. Use the above information and look in your power supply's manual to make sure that you are connecting a sufficient wattage or amperage to these adaptors. If you have to convert, you will find this useful ** amps x volts = watts ** watts/volts = amps. There are other types of adaptors than the ones shown in the picture; If it fills your power requirements and you need it, you can use it; but the ones pictured below are probably better. Some adaptors are only safe to use under certain conditions. By time you finish this guide, you should know enough to make intelligent choices.

An 18 gauge wire can handle 16 Amps (192 watts),
A Molex-8981 connector is rated for
18 AWG – 08 AMPS – 96 watts ** 16 AWG – 10 AMPS – 120 watts ** 14 AWG – 10 AMPS – 120 watts
If the Power Supply has enough power, these adaptors (in the above picture) are safe to use.
  • Connector; Some of the Molex connectors on the adaptors have two wires coming from its 12 volt pin. This is not a problem; you have 16 watts of elbow room before you exceed the connectors rating.
  • Power Supply line; I have been ask if a single power line with two Molex connectors on it, can safely connect to a GPU or CPU adaptor? If there is enough power coming from the power supply, Yes it can. A single line of 18 gauge wires connected using both Molex connectors is rated at 192 watts. The power needed from the power supply is listed under each adaptor’s picture.

Circuit path complexity: The simplest circuit path is "the power supply's circuit board / connecting wire / connector / receptacle / (graphics or main) circuit board". Every connector, adaptor, and extension you have in your computer has a probability of failing at some point in its life. With everything extra that you add, you increase that probability. The best scenario is to have a Power Supply with sufficient current that is equipped (as is) to directly connect to all of the power receptacles with-out the use of adaptors or extensions. But this is not always possible.

Power Supplies: If you do not load your power supply beyond 70% of its capacity, it will last longer and do its job better because it is in its most efficient operating range. Checking the loads to make sure you have the right power supply for the job you need it to do, is an easy way to help you computer last longer and run better. I have already done a lot of the work for you. Your part is to use this guide, your manuals, and pay attention to what you are doing. And don't forget to configure your case's airflow to where the power supply's cooling fan is being helped instead of fought (positive case pressure). Note: This only matters if the power supply draws its air from the case..

Some power supplies have more than one +12 volt rail. All 12 volt rails get there power from one circuit (the exceptions to this are few). The purpose of this power being separated into a multi rail system is to provide better protection. The logic is; three 10 amp breakers (rails) protecting a single 30 amp source are safer than one 30 amp breaker (rail); 30 amps (if shorted) can melt metal. The one big disadvantage of the multiple +12 volt rail system is, when you install any devices in your computer; you must manage the amperage load to each rail. The advantage is; it takes only a 10 amp problem to throw a breaker, this is better protection for the connected components. If your multiple rail power supply keeps shutting down, you have overloaded one rail. I prefer the simplicity of a single rail system.

The way a power supply works is: To turn the computer on, the main board supplies then maintains ground to the 5 volt GREEN wire on the 24-pin ATX power supply connector. To shut the computer off, the main board removes ground from that same GREEN wire. If the power supply has power going to it, the computer is alive (even though it’s not on). This is because 5 volts DC must be present at the GREEN wire to start the computer. As you can see, the main board is the component responsible for turning the computer on and off. When it feels an error, it removes the ground from the green 5 volts line to turn the system off. This is a safety fetcher used to minimize damage when there is a bad or incompatible component. You can find problems like this in the Event Viewer error log in the Computer Management utility. Path: Computer / Manage / System Tools / Event Viewer. If the power supply keeps turning off; an insufficient amount of power, a bad main board, or an incorrectly installed CPU cooler, is the most likely cause.

The GPU power connectors

This is a "GIGABYTE Radeon R9 280 3GB" Graphics card.

Connecting power to your graphics card: The PCIe x16 slot was design to power a video card drawing up to a maximum of 75 watts. That is adequate for most video cards, but some of the better cards, like high-end "gaming or workstation" cards, usually need quite a bit more power. The graphics cards that need more than 75 watts, have one or two additional power receptacles on them. The PCI Express auxiliary power connectors provide power directly from the power supply to the video card, they are a six-pin (2 × 3) and/or an eight-pin (2 × 4) connector. Some Main Boards have a 4 pin Molex receptacle near the PCIe graphics card slot; if you are using a 6 or 8 PCIe power connection(s), you do not need to supply power to the 4 pin Molex receptacle. This receptacle is there so that when you use a "no connector" type graphics card, you will get a good solid 75 Watts of power to the PCIe x16 slot. The six-pin connector has two 12 volt lines, and the eight-pin connector has three 12 volt lines. Each additional 12 volt input line adds about 40 watts to the 75 watts that is already at the PCIe slot. This list below is a general guide; all manufacturers do not do things exactly the same way. This is no standard set for this. Be aware that if the GPU power connectors wattage rating is close to the card's usage wattage rating, that graphics card will have a very limited over-clocking potential.

Auxiliary Power Connector Configuration for high performance graphics cards:
  • 75 Watts*******No connector
  • 155 Watts******One six-pin connector
  • 195 Watts******One eight-pin connector
  • 235 Watts******Two six-pin connectors
  • 275 Watts******One eight-pin connector + one six-pin connector
  • 315Watts******Two eight-pin connectors
  • 395 Watts******Two eight-pin connectors + one six-pin connector
If there is any combos that are not covered, each 6 pin connector adds 80 watts, and each 8 pin connector adds 120 watts.
Example: four 8 pin connectors, (4 X 120) + 75 = 555 watts

Let’s look at the pinout and discuss adaptors: The presents of a ground connection at sense A and B are used so that the graphics card can detect what types of connector(s) are attached; therefore how much total power is available. You can plug the six-pin connector into the eight-pin socket using an offset arrangement, but I would not do this. Depending on the design of the graphics card, it could either shut down or operate in a reduced functionality mode. If your existing power supply doesn’t feature the PCI Express auxiliary power connectors you need, you can use Y-adapters to convert multiple peripheral power connectors (normally used for drives) into a single six-pin or eight-pin PCI Express auxiliary power connector. The 6 pin to 8 pin PCI Express adapter will only work if the 6 pin PCI Express connector has a +12 volt wire at pin 2; although most good power supplies have this, the ATX standard is for it not to be there. Whatever adaptor you try to use, it needs to provide enough power to the GPU power connection. These adapters will not work well if the power supply is not capable of supplying the total power actually required to power all of the system tower’s components. The bottom line is, you are best off with the correct power supply; one that will easily supply enough power and directly connect to all of the devices with-out the use of adaptors. If a power supply has a connector, chances are, it has the power to support it.

On some power supplies, on the 8 pin PCIe connector, the 6th and 7th pin has a ground jumper coming from them to the 4th and 8th pins. Is this unorthodox looking cheat safe? Yes, it is very safe. The wire is the only component in this circuit that carries this extra load. An 18 gauge wire (the smallest available) will handle 18 amps or 216 watts. Its capacity is way higher than its usage will ever see. In the picture, the main wires coming from the power supply are 14 gauge, and the two grounding wires that are coming off of them are 16 gauge. The higher the gauge, the smaller the wire is.

Up-date: There must be a baseline for you to understand a subject, so all of the above information is still important because it applies to the (up to) 2013 stuff, and almost all of the cards that are out now. This information will also help you understand the newer cards that will be coming out. These new cards listed here cost over $1000. In the Quest for GPU Supremacy, AMD and NVidia have been producing DUAL GPU Graphics Cards that have made a “unofficial PCI-SIG Standards” update a necessity. The Devil 13 is a Dual Core R9 290X 8GB graphics card and is in the first picture at the beginning of this article. It has Four 8 pin connectors and says that each connector handles 150 watts. That was the first time I had ever seen a "wattage per line" rating that was that high (50 watts per line). That was just a few months ago. Now the Dual Core R9 295X 8GB graphics card Has been released and adheres to new up-and-coming unofficial standard. This card takes a special power supply, few of them are capable of these new numbers. This card needs 112 watts per line and 336 watts for each of the two 8 pin PCIe connectors. This opens a can of worms that only an enthusiast can understand. The average novice that buys this card will connect it to an inadequate power supply in spite of the warnings. All of the compatible power supplies listed are over 1500 watts. Read about it here: http://www.amd.com/Documents/Selecting-a-System-Power-Supply-for-the-AMD-Radeon-R9-295X2-Graphics-Card.pdf
This current supply system is still not official standardized (set by PCI-SIG). When you buy a high powered graphics card, it is to your extreme advantage to follow the instructions in the user manual that comes with it.

The CPU power connector

This is an "Asus maximus vii formula" Motherboard.

In the comments below, the above main board was brought to my attention. Seeing both the 4 pin and 8 pin together is a rarity. The 4 pin supplies 155 watts, and the 8 pin supplies 235 continuous watts. For most of the newer processors, even during extreme overclocking, ether connector would work fine. If you want to, you can even connect both the 8 pin and 4 pin CPU connections, all it will do is farther increase the wattage that is available to the CPU (315 watts). But this is not necessary, the 8 pin alone, provides more than enough power for any single CPU. If I have an 8 pin CPU connector on the power supply, and an 8 pin CPU power receptacle on the motherboard, I use it. I don't care weather my CPU needs the much power, or not. I do this because there is no down side, the 8 pin is the safest way to go; if I use it, I have no limits and no worries.

The 8 pin EPS12V CPU connection was originally made for multi CPU servers, and is meant to be more stable so critical servers don't fail under load. The 8 pin CPU receptacle started being installed on higher end main boards to increase compatibility so that server power supplies that only had an 8 pin CPU connector could be used in the build. This extra compatibility was needed because a large amount of power was required to power 45nm 4 core CPUs and multiple GPUs, extra power that only server power supplies had at that time. It now has become a standard.

If your main board has a CPU power receptacle, you must install at least a 4 pin connector before the computer will even boot up. If your main board has an 8 pin CPU receptacle, power supplies with ether a 4 pin or 8 pin CPU connector can be used, the 8 pin is preferred but often not necessary (no one likes to see the empty holes). Whither you have a 4 pin or 8 pin, all ground lines come from the same place and go to the same place, and all 12 volt lines come from the same place and go to the same place. The difference between a 4 pin and an 8 pin connector is the amount of available current. There are very few exceptions to the above rules, few main board can sense whither a 4 pin or 8 pin CPU connector is used, your main board's owner's manual is the best source for this information. The four-pin connector has two 12 volt lines, and the eight-pin connector has four 12 volt lines. Each additional 12 volt input line adds about 40 watts to the 75 watts that is already at the CPU slot. The list below shows these connectors continuous out-putt rating; it is a general guide; all manufacturers do not do things exactly the same way.
  • Main Boards with no CPU power receptacle will supply 75 continuous watts
  • Main Boards with a 4 pin ATX12V CPU power receptacle can supply 155 continuous watts
  • Main Boards with an 8 pin EPS12V CPU power receptacle can supply 235 continuous watts
NOTE: The peek or maximum watts rating is much higher than the continuous watts rating.

The CPU power connector supplies power to the transistors that control and regulate the voltage that the CPU uses. If an 8 pin CPU connector is needed, but you use a 4 pin instead, you will starve these rectifiers. This current starvation will not only cause read errors and blue screens, but can also cause the rectifiers and CPU to overheat and burn up. The +12 volt CPU power connection is used only for the CPU, it does not supply power to the memory; the memory power rectifiers get their power from a +5 volt line. There are very few CPUs that normally need the extra power the 8 pin EPS12V connector will provide. For most power users, the 4 pin ATX12V connector is sufficient for the needs of most CPUs. If your CPUs wattage rating, plus over-clocking needs is estimated to be close to 155 continuous watts, use a Power Supply with an 8 pin EPS12V connector to be safe. Of Course; If your Power Supply already has an 8 pin EPS12V connector, and your main board has that receptacle, it's stupid not to use it. But if you do not need the functionality of the 8 pin EPS12V connector, don't go out and buy another Power Supply just so you can fill in the extra 4 holes on your main board's 8 pin CPU power receptacle. If you do need the functionality of the 8 pin EPS12V connector, but a 4 pin ATX12V connector will supply more than enough power, a 4 pin to 8 pin adaptor is acceptable to use.

If your processor is an i7 4770 at the stock clock, according to the specifications, it uses a maximum of 84 watts. All CPUs use quite a bit less than their max during their normal operation. Even if it is heavily overclocked (4.8 GHz), it will use less than a maximum of 130 watts; for this i7, an 8 pin connector would be overkill. If half of the EPS12V 8 pin connector on the main board is covered, this is a sure sign that a minimum of the 4 pin is required, but the 8 pin connector is optional. A power supply with a 4 pin ATX12V connector will provide more than enough power for this CPU's needs.

I have seen other writings that suggest "192 watts for 4 pin" and "288 watts for 8 pin". They discuss the current capacities of the connector and its connecting wire's gauge. I am more incline to believe my numbers because they are based on the limitations of the weakest component in the circuit path; the metal etchings (traces) and mofsets on the printed circuit board.

If you liked this guide, I have written others that you may also enjoy.
A guide on how to fix Heat Problems
How to Solder Electronics
How To Choose A LiPo Battery

Comments (34)

Its been over a month and there are no comments.
I did a fair amount of editing on it today,
there is always room for improvement.

Did any one find any of this information useful?
I think no comment means no-one could find any fault with your information. I found the article to be very educational. I would have liked to see more information about the case where the needed power connectors are not available - when a Y-adapter would be used (given that the existing power supply has enough remaining power). How does a Y-adapter work? How much power is supplied on the pins of the Y-adapter and how much power does a typical drive take if one exists in the chain?
You have some good questions here.
I put in another section in the guide that has the answers you ask for;The 6 and 8 pin adaptors.
Thank you for your help.
I mentioned drives because sometimes those molex connectors may come from a 12V line that has drives attached to them and there are no other free molex connectors.

I noticed the 8 pin GPU to molex adapter uses one molex 12V line to supply two 12V lines of the 8 pin connector. Do we need to worry about some lines of the 8 pin connector having less power than others? In other words, does the 12V molex line that is supplying two 8 pin 12V lines need to be 80W (and the other molex line is 40W) or is it ok if both molex lines are 60W each? In any case, I suppose if you don't have 2 free molex lines, then the molex line with the fewest drives should be connected to the Y adapter half that is supplying two lines to the 8 pin connector?

At http://en.wikipedia.org/wiki/Power_supply_unit_(computer) it is explained that some power supplies may have multiple 12V lines coming from the same source so in that case it wouldn't matter as long as the source can do 120W (if no other devices are using that source).
A good education on power supplies is an asset.
That is a very smart observation. Yes, the Molex with one 12 volt line coming from it needs to provide 40 watts, and the Molex with two 12 volt lines coming from it needs to provide 80 watts. We do need to worry about that.
The source is only part of the path, the capacity of the wire and connector are also important. Sometimes the source is split into rails, and these rails need to be managed. I added more about this in the guide. Thank you for you input.
Hi Luke Cool - thanks for putting your post up. I am building a rig I intend to overclock and fold with - so power and heat will be a priority in the approach to it.

I have two pretty basic questions about setting up this rig.

There are two CPU power connectors on the Maximus VII Formula board - one is the eight pin and I have connected this to the EVGA 850 SuperNOVA Gold-Certified PSU,

If I intend to not only overclock the 4790K CPU to about 4.6GHz *and* I will have two EVGA 780 6GB overclocked as well should I:

1) Connect the PSU to the second 4-pin connector for CPU power on the mobo that ASUS insists is only for EXTREME overclocking?
2) The power projections (pcpartpicker and a couple of other sites) put this rig at a peak demand somewhere around 725-735 watts, give or take a few watts. Obviously that is over the 70% figure you give as a recommendation not to exceed if long life of the PSU is desired - I am wondering if it might be better to pull it and sub it with a SIlverstone Strider 1500 that I can get my hands on from a friend for real cheap. Stick with the new EVGA and see how it goes or get the 1500 and move the 850 (it would go into a smaller box in my folding farm?)

Thanks again for your contributions - +REP for you my friend!
1) It will not hurt anything for the 8 pin CPU connector.(EPS-12V) to be used, even if you are running a cheap underclocked 2 core CPU. The only difference between the 4 pin and the 8 pin is, with the 8 pin, more wattage is available to the CPU.
2) The 70% figure will keep your power supply in an efficient operating range and keep it from overheating. There is no cut and dry answer to the second question. There are people that have computers that are capable of a 750 watt peak usage, but their average wattage used is well below 400 watts, and they rarely go over 500 watts peak. For this person, an 850 watt power supply is fine. In your case, you are probably a power user. If I was on the line like you are, and I could get a good deal on a 1500 watt PS, I would definitely up-grade.
Thanks for the considered responses - I did get the 1500 used but it was in a machine until a few weeks ago and was working fine. It was also tested and appears to be running well.

However, one last question - concerning the 8 pin and 4 pin CPU connections - is it recommended to have *both* connected when overclocking? ASUS seems to be saying in the Maximus VII Formula manual to connect only if extreme overclocking is being attempted? What constitutes extreme overclocking in a GPU like the 780? Does one go by voltage as a measuring stick? Or is it, say, something like 1000MHz in the base clock and/or 1050MHz in the boost? (Also remember that there will be two of these big mamas in the rig - not just one.)
Connect the 8 pin CPU connector only. Your Intel 4790K die is small, 22nm. The smaller dies use less voltage and power, there-for runs cooler. This is why your CPU's max power consumption is rated for only 88 W. The 4 pin ATX12V CPU power receptacle can supply 155 continuous watts, and the 8 pin EPS12V CPU power receptacle can supply 235 continuous watts. For you, ether connector would work fine, even during extreme overclocking. You can even connect both the 8 pin and 4 pin CPU connections, all it will do is farther increase the wattage is available to the CPU (315 watts). But as you can see by your CPU's max power consumption, this is not necessary. I take questions like yours seriously. I downloaded and read you motherboard's manual before answering you the first time. But I know how this circuitry is configured. I am an electronics technician with 35 years experience. If I have an 8 pin CPU connector on the power supply, and an 8 pin CPU power receptacle on the motherboard, I use it. I don't care weather my CPU needs the much power, or not. I do this because there is no down side, the 8 pin is the safest way to go; if I use it, I have no limits and no worries.

The 4 pin ATX12V and the 8 pin EPS12V CPU power receptacle supplies power to the CPU only. It has nothing to do with memory or GPU power consumption.

Increase ether frequency or voltage will increases the amp draw of your CPU or graphics card. Extreme overclocking is having to go above the CPU or GPU's stock operating voltage to stabilize its overclocked frequency
Understood - thanks for the advice. Just to let you know - I wasn't doubting anything you wrote, I was merely unsure if I had made myself clear.
I question everything too, untill I understand.
With every good question that gets ask, I see room for improvement in the guide.
I added a new section in the guide that may help you.
Understanding how the system is set up:
Thanks Luke, now I know what to do, and not to do, what to go for, and not. Keep writing those articles.

And.. the explaining you did with this article, wow, I mean, you're supurb.

Thank you for your kind words, I enjoy this type of writing.
nice read and very informative,and yet i don't know what to do..
Basically..kinda scared i gues lol.
oke my motherboard is an p8h67-m pro..wich has a 8 pin cpu power connector available.and i use an Intel i5 2500.
My psu is an cooler master GM 750 with 8 pin cpu.
For more then a year i been using just 4 pins for the cpu power with no problem at all..
my Question,should i just plug in the other 4 pins also..even tho i never had a problem with just 4?
It is said GPU takes 75W from the motherboard over PCIe connector. Does this happens always, even if the power is connected directly to the GPU card? Reason for my question is 4-Way SLI. Does every card take then its 75W from the motherboard, apart of the power from its connectors? If so, then cards would be taking 300 W from the motherboard.
You can plug the second 4 pins in if you want to. If you are over clocking, it is much safer. But for general use, the extra power is not necessary. Personally, if the motherboard and the power supply have an 8 pin connector, I use it
Yes, it does happen always. Every card does take then its 75W (3.3 V × 3 Amp + 12 V × 5.5 Amp) from the motherboard, apart of the power from its connectors. This is the standard for the PCIe slot. For 4-Way SLI, that's 300 watts. A set-up worthy of 4-Way SLI, demands a kick-butt power supply..
Luke, awesome guides! Any advice or guides for someone who is going to make his own 24pin ATX cables for custom sleeving? I know the newer PSU's have a 10+14 slot for one end of the ATX cord and the 24 pin side going to the MOBO. Someone told me there are double wires that have to be soldered and whatnot.
You can make a pin removal tool out of a small metal tube you can find at any good hobby store. The tube has to be small enough to fit around a pin and compress the locks, then the pin slides right out.There is no soldering necessary unless you are going to customize the lengths of the cables. If you do that, even though you are installing custom sleeving, use heat shrink to reinsulate the wire. Don't forget to stagger the connections (don't do them all in one place) a big lump in the harness looks stupid. If you need help with this, I have written a guide on "How to Solder Electronics"; you will find a short cut to it at the end of this article.
So, question if you have a second -- I have a PS that has two 8-pin PCI-E outputs, and 4 6-Pin "Sata" outputs. I am completely unsure the difference.
The manual I have only says "this is how you install your PS" which is not terribly useful.
My GPU has a 8 pin input and a 6 pin input. I don't have (nor do I know if it's appropriate) a 8-pin to 6-pin connector, so what I was using was and 8-pin that splits into two 4-pin molex connectors that I then have connected back to a two 6-pin connectors, that I than use one to power the GPU.
I ask because recently I thought "heh, i can use the SATA 6-pin port to power my GPU". That did not end well for me.
So, I'm a bit confused as to the difference between "SATA" and "PCI-E" (well, I know the difference, but for power purposes I'm confused).
Great page BTW; I did learn quite a bit.
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