I am trying to build a computer, placing an ASUS P8H67-I DELUXE in a custom retro Commodore 64 case.

The case is an extra small form factor which can accommodate the Mini ITX board, but it requires an external power supply, similar to the power-bricks that laptops use.

I am looking at different power supplies and like these, but I cannot figure out whether/how to power this system, because they provide a 24-pin connector, but the motherboard has a 4-pin connector as well.

Is the 4-pin connector optional or is it required? If it is required, how can I provide power for this system?


The 24 pin EATX power connector...

The 24 pin main power connector was added in ATX12V 2.0 to provide extra power needed by PCI Express slots. The older 20 pin main power cable only has one 12 volt line. The new 24 pin connector added one line apiece for ground, 3.3, 5, and 12 volts. The extra pins made the auxiliary power cable unnecessary so most ATX12V 2.x power supplies don't have them. The 24 pin connector is polarized so it can only be plugged in pointing in the correct direction.

Enter image description here

The separate 4-pin ATX 12 V that is on your board...

Older computers put most of their load on 3.3 and 5 volts. As time passed, computers drew more and more of their load from 12 volts. Before this power cable was introduced there was just one 12 volt line provided to the motherboard. This cable added two more 12 volt lines so more of the load could be shifted to 12 volts. The power coming from this connector is usually used to power the CPU but some motherboards use it for other things as well. The presence ‎of this connector on a motherboard means it's an ATX12V motherboard. For dual 12 volt rail power supplies, this connector provides the voltage referred to as 12V2. The power cable which plugs into the 4 pin connector has two black wires and two yellow wires. This cable is sometimes called an "ATX12V" cable or "P4" cable although neither of those are technically accurate descriptions.

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So there you go. What they are for with images and links.

More information us in Super User question Core i3-2100 with 65W power supply?.

Using this same PSU calculator, with the information you provided CPU, two sticks DDR3, one SSD flash drive) I came up with 146 watts required. So, the Pico 160 watt mini PSU should be enough.

  • Thank you. So im using a pico power supply where the cord has a brick. would the first one be all it would need to be compatible? something like this i think logicsupply.com/categories/power_supplies/… – Geeks On Hugs Jun 3 '12 at 23:14
  • @GeeksOnHugs the PicoPSU-80? It says "for small PC designs using a single 12-volt power source" which doesn't fit the power requirements of that motherboard, since it not only has the 24 pin connector, but the 4 pin connector as well... and the presence of that 4 pin connector shows that you will need more than one 12v power source for the board. the PicoPSU-160-XT further down has one of those "p4" connectors, and depending on the CPU you use, might be enough logicsupply.com/products/picopsu_160 – Bon Gart Jun 3 '12 at 23:43
  • sweet ty :-) im using an i3 3.1 ghz, 8gb ram, 64 gb ssd...running linux...i might downclock the cpu depending on how easy that is to do – Geeks On Hugs Jun 3 '12 at 23:51
  • I don't expect getting a 160watt Ac/Dc power adapter will be too difficult, but I don't think it will be all that prevalent either, considering that 120 watts is pretty hefty for a laptop adapter. That said, if you keep the demands on that PSU minimal, that 160 should be fine without underclocking. – Bon Gart Jun 3 '12 at 23:56
  • And this processor? ark.intel.com/products/53422 it's a 65 watt CPU. Just putting that out there. Not that there is anything wrong with a 65 watt CPU. – Bon Gart Jun 4 '12 at 0:05

Okay, now that we have more information, the question is completely different. What you are asking is if you can put this motherboard in a case like this, with a PSU like this.

If you look at section 1.7.2 (page 1-10) of the manual where it discusses the EATXPWR and ATX12V power connectors, it explicitly states:

  • For a fully configured system, we recommend that you use a power supply unit (PSU) that complies with ATX 12 V Specification 2.0 (or later version) and provides a minimum power of 350 W.

  • DO NOT forget to connect the 4-pin ATX +12V power plug. Otherwise, the system will not boot up.

  • We recommend that you use a PSU with higher power output when configuring a system with more power-consuming devices. The system may become unstable or may not boot up if the power is inadequate.

What this means is that the PSUs you are looking at are not going to work. They are unlikely to conform to ATX 2.0, and not only do they not have the ATX12V connector, but they max out at around 160W which is almost half of the minimum needed for a board (and CPU) like this.

You are going to have to either contact the manufacturer of the case to ask them about compatible PSUs (I notice a conspicuous lack of power information on the site), or else perform a case mod to find a way to fit in or connect to a typical desktop PSU.

Also, a word of warning: a case that small is almost certain to have heat-dissipation issues (there is also an equally conspicuous lack of cooling information on the site). You will want to ask them about cooling and airflow while you are at it, otherwise you will need to find a way to make sure it does not overheat (cut more holes in the case?)

Technical details about the actual connectors.

The extra 4-pin (sometimes eight) connector is for the CPU. It provides a dedicated 12V supply to the CPU for when it needs it. That way, the CPU does not draw from the same source as the rest of the components in the system. It is usually called the P4 power connector because when the P4 was introduced it was so power-hungry that it needed more power, so the ATX standard had to be updated to accommodate it.

enter image description here

In fact, because video-cards became more powerful and more power-hungry as well, many modern PSUs (especially the fancy, high-end, modular kinds) even supply even more than the minimum of two 12V rails that the ATX specification calls for (though some don’t actually provide two completely separate rails).

There is also a 6-pin connector that can provide extra power to the PCI-e bus. enter image description here

As standards loosen and PSU manufacturers start diverging and adding new features to accommodate increasing power-demands, the number of different PSU connectors continues to increase.

(You can find out the specs by looking at he sticker on the side of the PSU. It will indicate the maximum current that each of the rails can handle.)

  • im using a small retro c64 look case commodoreusa.net/CUSA_C64.aspx which requires an external power supply like a laptop. can u point me to a suitable example? – Geeks On Hugs Jun 3 '12 at 23:22
  • I dunno. Based on superuser.com/questions/277052/… 126 watts could do it with the same processor and motherboard as Geeks on Hugs is using. – Bon Gart Jun 4 '12 at 0:08
  • That may be, but I doubt that ASUS would be willing to provide any assistance in that case, so it’s up to GoH and how willing they are to take chances and/or whether they can afford to pay for replacements if something breaks. (In my opinion, unless you are rich and don’t mind voiding the warranty, it’s best to use a system correctly until the warranty expires, and then start experimenting when have nothing to lose.) – Synetech Jun 4 '12 at 0:13

As the motherboard specification says, it's a 4-pin ATX 12V power connection. Pretty much every modern motherboard has a separate 12V power connector that's either a 4-pin or an 8-pin. The primary purpose of this power connector is to power the VRM that supplies power to the CPU. It must be connected to the power supply for the motherboard to work.

  • The power supply I'm considering says "12V DC input power supply that plugs directly into a 24-pin ATX connector on a Mini-ITX mainboard." so what would I plug into the second connection? – Geeks On Hugs Jun 3 '12 at 22:43
  • @GeeksOnHugs, you plug the 24-pin connector to the 24-pin socket and the 4-pin yellow/black connector to the 4-pin socket. – Synetech Jun 3 '12 at 22:57
  • @Synetech: You are incorrect. It is not the extra 4 pins that were added to the 20 pin connect. Look at the linked specification and the excerpt from it in the question. – David Schwartz Jun 3 '12 at 23:04
  • @GeeksOnHugs: The 4-pin 12V connector. If the power supply doesn't have one, you can't use it with this motherboard. (What model is it?) – David Schwartz Jun 3 '12 at 23:05
  • Im wanting to use an external power supply [or rather i have to for this case...like i think with a brick on the coard])...can you point me to a suitable example? – Geeks On Hugs Jun 3 '12 at 23:19

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