ATX12V vs EPS12V dilemma

[kubn2]

Hey,
So I'm in the middle of collecting parts for my tower server and as per Motherboard (which is supermicro) manual it requires 2x 8pin CPU connectors which are NOT ATX12V but EPS12V. I found Corsair RM750x to have two EPS12V connector at least that's what they say on their website: https://www.corsair.com/us/en/Categories/Products/Power-Supply-Units/Power-Supply-Units-Advanced/RMx-Series/p/CP-9020179-NA#tab-tech-specs however I found topic on other forum from 2011 where someone used different supermicro motherboard and Corsair Builder Series CX600 and turned out that it doesn't work as it was ATX12V however on their website corsair still list this PSU to have one EPS12V connector: https://www.corsair.com/us/en/Categories/Products/Power-Supply-Units/Builder-Series™-CX600/p/CMPSU-600CX#tab-tech-specs So I'm a little bit worried what if again Corsair list newer PSU like RM750x to have EPS12V but instead they have ATX12V? Is there ANY way to tell for sure that this PSU has EPS and this doesn't? If RM750x doesn't have EPS or it's not possible to tell for sure, can you advice me on any other PSU that for sure have two EPS12V 8pin CPU connectors?

[mariushm]

EPS is the name of the 8 pin CPU connector.

 

ATX12V used to be the name for the 4 pin CPU connector or maybe better put would be the extension to the atx standard which introduced 4 pin CPU power cable, and the decision to power processor VRMs from 12v instead of 5v as it was common before the Pentium 4 days.

 

Most 650w and higher power supplies will come with two EPS (8 pin) cpu connectors , or one EPS and one 4+4 ... if they don't come with 2 cables, with modular power supplies you have the option of buying an extra cable with the EPS 8 pin cpu connector.

 

For example, Seasonic power supplies have 3 or more "universal" 8 pin headers on the power supply case, and you can plug either a cable with EPS (cpu 8 pin) connector at the end, or a cable with pci-e 6 pin / 8 pin connectors.

 

Seasonic and beQuiet are two of the brands that I know they list the cables and number of connectors on their websites.

 

 

[kubn2]

2 minutes ago, mariushm said:

Most 650w and higher power supplies will come with two EPS (8 pin) cpu connectors , or one EPS and one 4+4 ... 

 

 

If I understand that correctly, when the 8pin connector isn't 4+4 (so one wire doesn't split at the end) it's EPS connector if the connector at the end split to 4+4pins its ATX12v, is that correct?

[mariushm]

No.

 

The 8 pin cpu connector is EPS and it comes from servers. It has migrated to regular home user computers at some point. The connector is KEYED, so you don't insert pci-e connectors into it. By key, I mean the shape of the holes:

 

 

In the old days, ATX power supplies came only with the 20 pin / 24 pin connector and molex / floppy connectors. 

In the times of Pentium 4, because the Pentium 4 was so power hungry, the organization that made the ATX specification released a new version of the specification which introduced the option for motherboard manufacturers to use a 4 pin CPU connector which gives 12v to the circuit which powers the processor.

So this "extended" specification was called ATX 12v  ... but because the only significant change was the introduction of this 4 pin CPU connector, this CPU connector got to be called by some as the ATX12V connector / header / cable, whatever.

 

See the specification, on page 6-7 and on page 28 :  https://xdevs.com/doc/Standards/ATX/ATX12V_Power_Supply_Design_Guide_Rev1.1.pdf

 

Quote

1.2.1. ATX12V
A new superset of the original ATX power supply has been defined. Named “ATX12V,”  this new power supply is comprised of a standard ATX unit plus the following enhancements:
• Increased +12 VDC output capability. Motherboard components with unique voltage requirements are increasingly expected to be powered via DC/DC converters off the +12 VDC power supply output.

[...]

• Power Connectors. To enable the delivery of more +12 VDC current to the motherboard, a new 4-pin receptacle/header combination—the +12 V power connector—has been defined. The presence of the +12 V power connector indicates that a power supply is ATX12V; the absence of the +12 V power connector indicates that a supply is ATX.

[...]

 

And on page 28 you'll see the 4 pin shape, which looks like this :

 

 

You will see that the LEFT half of the EPS connector has the same KEY-ing, all four holes are same shape, that's done on purpose.. 

 

Power supply manufacturers can now take one EPS connector and make it possible to separate it into two halfs , 2 4 pin parts, and you can use one 4 pin part to plug into a motherboard that only has a 4 pin CPU connector.

 

When processors got even more power hungry, motherboard manufacturers adopted the EPS connector from servers and brought it to regular motherboards, they didn't invent a new standard.

 

So... computer power supplies have EPS connectors.... the 8 pin CPU power connectors.  SOME 8pin CPU power connectors  MAY split into 2  4 pin pieces, to allow someone to power a motherboard that has only a ATX12v 4 pin CPU power connector.

 

Am I clear enough ?