24-Pin ATX Power Supply Connector Pins (June 2026)

When you are building a PC or swapping out a power supply, the first thing you notice is a thick bundle of wires terminating in a wide plastic block. That block is the main ATX power connector, and the question most builders ask is simple: how many pins are in the power supply connector of most motherboards today? The answer is twenty-four.

A standard modern ATX motherboard uses a 24-pin main power connector, plus an additional 8-pin EPS connector that delivers dedicated power to the CPU. Those two plugs together form the backbone of every desktop power delivery system.

Twenty-four pins is more than just a number. Each pin carries a specific voltage rail, a control signal, or a ground path. Knowing what those pins do helps you troubleshoot a dead build, test a PSU outside the case, or simply choose the right modular cable from a bag of look-alike cords.

In this guide, we will explain the history of the ATX standard, break down the full 24-pin pinout, cover the auxiliary CPU power connectors, and look at where the industry is heading with ATX 3.0 and the 12VHPWR connector in 2026.

How Many Pins Are in the Motherboard Power Supply Connector?

The short answer is twenty-four. A standard modern ATX motherboard uses a 24-pin main power connector as its primary power source. The connector is physically keyed and latched so it can only be inserted one way.

You will also find an additional 8-pin EPS connector near the CPU socket that supplies dedicated 12V power to the processor. Older boards and some small form factor designs may still use a 20-pin connector, but the 24-pin standard has been the norm since 2003.

Some power supplies ship with a 20+4 pin cable. The four-pin block detaches, which lets you power older 20-pin boards without leaving extra pins dangling.

This backward compatibility has kept the transition painless for almost two decades. If you are looking at a board from the early 2000s, you might see the 20-pin socket, but anything built in the last fifteen years will almost certainly have the full 24-pin header.

ATX 101

ATX stands for Advanced Technology Extended. Intel introduced this specification in 1995, and it redefined how desktop computers were built.

Before ATX, motherboards used the older AT and LPX layouts, which had clumsy power switches, inconsistent mounting points, and I/O ports that were scattered across flying cables. The ATX standard brought a unified layout with a single rectangular I/O area at the back, standardized screw holes, and a keyed power connector that could not be forced in the wrong way.

A full-size ATX board measures 305 mm by 244 mm. Smaller variants such as micro-ATX and mini-ITX shrink that footprint, but they still rely on the same 24-pin power connector and the same rear I/O layout.

If you want to see how those sizes compare, our guide on ATX form factor specification covers the differences in detail. There is also Extended ATX, or E-ATX, which stretches to 305 mm by 330 mm.

That extra space is common on dual-socket workstation boards and flagship enthusiast models like the ones discussed in our E-ATX motherboards guide.

Intel has updated the ATX specification many times since 1995. ATX12V version 2.53 arrived in 2020, improving efficiency guidelines and standby power rules.

In 2022, Intel released ATX 3.0, which was a major leap forward designed to handle the enormous power spikes of modern GPUs. The 20-pin power connector was the standard for years, but it was replaced by the 24-pin version in 2003 as CPUs and expansion slots began to demand more current than the older design could safely deliver.

Power Supply and Voltage Rails

An ATX power supply delivers three main voltage rails to the motherboard: +3.3V, +5V, and +12V. The 12V rail is the workhorse of any modern build.

It feeds the CPU through the voltage regulation modules, powers graphics cards, and runs hard drives and SSDs. The 3.3V rail handles chipset logic and some storage controllers, while the 5V rail supplies USB ports, fans, and legacy peripherals.

There is also a +5VSB standby rail. It stays active whenever the PSU is plugged into the wall, even if the PC is turned off.

This tiny trickle of current keeps the real-time clock ticking, preserves your BIOS settings in CMOS, and enables features like wake-on-LAN and USB charging while the system sleeps. The PS-ON# signal, carried on the green wire of the 24-pin connector, tells the PSU when to wake up from standby and deliver full power.

The Power Good signal, usually the gray wire, confirms that every voltage rail is stable before the motherboard releases the CPU from reset. Without Power Good, your system would attempt to boot before the PSU was ready, leading to random crashes or failed starts.

Power Connection to the Motherboard

Before ATX, the AT and LPX form factors used two six-pin connectors that looked almost identical. It was easy to swap them by accident, and when that happened, the resulting short circuit could destroy the motherboard.

ATX solved this problem with a single large connector that is keyed so it only fits one way. A plastic latch and a beveled edge on the socket make backward insertion impossible.

The 24-pin ATX connector is the main highway for power. It carries 3.3V, 5V, 12V, ground, and the control signals we just discussed.

Because the connector supplies 3.3V directly, the motherboard no longer has to step down 5V, which improves efficiency and reduces heat. The connector itself uses the Molex Mini-Fit Jr family, specifically the 5569 series housing, with a 4.2 mm pitch between pins.

This is the same connector family used for the 8-pin EPS and 6-pin PCIe plugs, which is why the housing looks familiar even though the pinouts are different. Alongside the power connector, the ATX standard also reorganized the rear I/O panel.

Older AT boards forced builders to route serial and parallel ports through flying cables that dangled from the motherboard to unused expansion slots. ATX placed every port in a single rectangular block at the back of the case.

An I/O shield, usually a thin metal plate that snaps into the chassis, fills the gap around those ports to block dust and reduce electromagnetic interference. If you are new to motherboard layout, our article on motherboard fundamentals explains how every slot and header fits together.

CPU Auxiliary Power Connectors

The 24-pin main connector does not carry enough 12V current to feed a modern CPU on its own. A high-end processor can pull over 200 watts under load, and pushing that much current through the main connector would create excessive heat and voltage sag.

To fix this, the ATX12V specification added a dedicated CPU power connector that sits near the top of the motherboard, close to the voltage regulation modules. Budget and older boards often use a 4-pin ATX12V connector.

It carries two +12V lines and two ground lines. Mid-range and high-end boards almost always require an 8-pin EPS connector.

This plug is essentially two 4-pin blocks fused together, and it doubles the 12V delivery capacity to the CPU. Enthusiast boards built for extreme overclocking sometimes include a second 8-pin EPS socket or even a 4-pin plus 8-pin combination.

You can see real-world examples of this layout in our roundups of high-performance motherboards with 8-pin CPU power and 8-pin CPU power connectors.

The 8-pin EPS connector and the 8-pin PCIe power connector look similar, but they are not the same. The EPS plug has a square-and-rounded keying pattern that differs from the PCIe plug, and the pinouts are completely different.

Plugging a PCIe cable into the CPU power socket can destroy your motherboard or PSU. Always read the label on modular cables before connecting them.

If your PSU only has a 4-pin ATX12V cable and your board has an 8-pin socket, check the manual. Many 8-pin sockets will run fine on just half the connector, though you may see slightly higher temperatures under heavy all-core loads.

24-Pin ATX Power Connector Pinout

The 24-pin ATX power connector, sometimes called the P1 connector, is arranged in two rows of twelve pins. The table below lists each pin, its wire color, the voltage it carries, and its function according to the ATX12V v2.0 and later specifications.

Pin	Wire Color	Voltage	Function
1	Orange	+3.3V	+3.3V rail
2	Orange	+3.3V	+3.3V rail
3	Black	COM	Ground
4	Red	+5V	+5V rail
5	Black	COM	Ground
6	Red	+5V	+5V rail
7	Black	COM	Ground
8	Gray	Power Good	Power Good signal
9	Purple	+5VSB	Standby power
10	Yellow	+12V	+12V rail
11	Yellow	+12V	+12V rail
12	Orange	+3.3V	+3.3V rail
13	Orange	+3.3V	+3.3V rail
14	Blue	-12V	-12V rail (legacy)
15	Black	COM	Ground
16	Green	PS-ON#	Power on signal
17	Black	COM	Ground
18	Black	COM	Ground
19	Black	COM	Ground
20	White / NC	N/C	Reserved (formerly -5V)
21	Red	+5V	+5V rail
22	Red	+5V	+5V rail
23	Red	+5V	+5V rail
24	Black	COM	Ground

Looking at the table, you can see why the 24-pin design was necessary. The extra four pins, numbered 21 through 24, add more +5V and ground capacity.

Spreading current across multiple pins and wires reduces resistance and heat, which is critical when a system is drawing several hundred watts. The orange wires carry 3.3V, the red wires carry 5V, and the yellow wires carry 12V.

Black is ground, and the green, gray, and purple wires are control signals. The PS-ON# pin on the green wire is the one that tells the PSU to turn on.

If you want to test a power supply outside a case, you can short pin 16 to any ground pin with a paper clip or jumper wire. This is a common troubleshooting step when you suspect a dead PSU.

The Power Good signal on the gray wire tells the motherboard that all voltage rails are within tolerance. The board will hold the CPU in reset until this signal goes high.

If Power Good is missing or slow, you get boot loops or random shutdowns. The purple +5VSB wire is always live as long as the PSU is plugged into the wall.

This is why your keyboard LEDs might still glow after you shut down Windows. The -12V rail on pin 14 is largely obsolete for consumer hardware today, but it remains in the standard for legacy serial port compatibility.

Pin 20 is reserved. In the original 20-pin connector, it carried -5V on a white wire, but modern ATX12V supplies removed that rail because modern hardware no longer needs it.

Modern ATX Power Connector and ATX 3.0

Since 2003, the 24-pin ATX connector has been the universal main power interface for consumer desktop motherboards. Most power supplies sold today ship with a 20+4 pin design.

The four-pin block can detach, which lets you power older 20-pin boards without leaving extra pins dangling. This backward compatibility made the transition painless and is why you still see 20+4 cables on brand-new PSUs.

In 2022, Intel launched the ATX 3.0 specification. It was written specifically to handle the massive power spikes of modern graphics cards.

The standout feature is the 12VHPWR connector, a 16-pin plug that can push up to 600 watts through a single cable. Twelve of the pins carry +12V, and four smaller sense pins let the GPU and PSU communicate about available power budget.

The sense pins tell the card whether the cable is rated for 150W, 300W, 450W, or 600W, and the GPU adjusts its power draw accordingly. ATX 3.0 also introduced much stricter transient response requirements.

A power supply must now survive brief power spikes that are up to three times its rated wattage. This matters because a GPU like the RTX 4090 can spike to well over its average TDP for just a few milliseconds.

Older PSUs without ATX 3.0 protection could shut down or trip their overcurrent protection during these spikes. If you are buying a PSU for a high-end build in 2026, an ATX 3.0 unit with a native 12VHPWR cable is a smart choice.

You can learn more about how modern boards handle power delivery in our coverage of 24-pin ATX power connector implementations.

Frequently Asked Questions

Conclusion

Most motherboards today use a 24-pin ATX power connector as their main power source, paired with an 8-pin EPS connector for the CPU. The 24-pin layout has been the standard since 2003, and the 20-pin format is now rare outside of retro builds.

With ATX 3.0 and the 12VHPWR connector, the standard continues to evolve to meet the power demands of modern GPUs. Whether you are building a new rig or troubleshooting a boot issue, understanding how many pins are in the power supply connector and what each pin does will make you a more confident builder.