What is an EPS connector?
The EPS connector, also called EPS12V or simply the CPU power connector, is the 8-pin cable from the power supply that feeds +12 V to the processor. It plugs into a socket near the CPU socket, usually at the top-left corner of the motherboard, labeled something like ATX12V, CPU_PWR or CPU1. The board's voltage regulator module (VRM) converts that 12 V into the much lower voltage the CPU runs on.
The name comes from the EPS12V power supply specification published by the Server System Infrastructure (SSI) forum for servers and workstations. Desktop boards adopted the same 8-pin connector as CPUs drew more power. (EPS is also the file extension for Encapsulated PostScript graphics, an unrelated meaning.)
Versions and pin layouts
| Connector | Pins | Notes |
|---|---|---|
| ATX12V (P4) | 4: two +12 V, two ground | The original CPU power connector from the Pentium 4 era; older and budget boards |
| EPS12V | 8: four +12 V, four ground | Standard on most desktop boards |
| 4+4-pin | Two 4-pin halves that clip into one 8-pin plug | One half for a 4-pin socket, both for an 8-pin socket |
| Extra 4-pin or 8-pin | A second socket next to the first (8+4 or 8+8) | High-end and overclocking boards; the manual says whether it's required |
Don't mix it up with PCIe power
Graphics cards use an 8-pin PCIe power connector, often built as 6+2 pins. It looks similar to the 8-pin EPS plug, but the two are keyed differently and their +12 V and ground pins are in different positions. They shouldn't fit each other, so never force one in: a forced fit can short the supply and damage the board, card or PSU.
- PSU cables are usually labeled CPU or PCIe (sometimes VGA). Match the label.
- A 4+4 plug splits into two equal halves; a 6+2 plug splits into a 6-pin block and a 2-pin block.
- On a modular PSU, the CPU and PCIe sockets on the power supply can look alike. Follow the labels, and never use modular cables from a different PSU, since pinouts at the PSU end aren't standardized.
Troubleshooting
A missing or loose CPU power cable is a classic new-build mistake. The PC powers on, fans spin and lights come on, but it never POSTs and there's no display, because the CPU has no power. Many boards light a CPU debug LED or show a POST code. Check that the CPU cable is plugged in and latched, and that every pin the manual requires is connected.
For the CompTIA A+ exam
Core 1 (220-1201) objective 3.5 lists power connectors among the motherboard connector types, and objective 3.6 covers installing a power supply, including the 20+4-pin motherboard connector and the 12 V output. Know the 4-pin or 8-pin CPU connector as separate from both the 24-pin main connector and the 6+2-pin PCIe graphics connector. Fans spin but no POST after a build often means the CPU power cable isn't connected.