How Intel's ATX 3.0 Design Guide Classifies PCIe Auxiliary Power Connectors for GPUs

Thu, 23 Apr 2026 22:22:49 +0800

In ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide 2.1a, Intel groups the auxiliary power connectors used by PCI Express Add-in Card devices into three categories:

PCIe 2x3
PCIe 2x4
12V-2x6

In practice, the most common Add-in Card here is a discrete graphics card. The document also makes it clear that these connector types cover a power range from 75W all the way up to 600W.

1. The short version first

If you only want the key distinction, you can think of them like this:

2x3 corresponds to the familiar GPU 6-pin, rated for 75W
2x4 corresponds to the common GPU 8-pin, rated for 150W, and backward-compatible with 2x3
12V-2x6 is the newer high-power GPU connector, with support up to 600W

The real dividing line is not just wattage, but also this:

2x3 / 2x4 still follow the traditional auxiliary power approach
12V-2x6 folds high-power delivery, insertion-state detection, and sideband signaling into the standard itself

2. `PCIe 2x3`: the old 6-pin, defined here as `75W`

On this page, Intel defines the 2x3 Auxiliary Power Connector as an auxiliary power connector that can provide 75W for a PCIe add-in card.

The key details include:

The design target is 75W
The maximum rated value is 8.0A/pin
The cable gauge listed is 18 AWG
One Sense pin needs to be tied to ground so the graphics card can detect whether a 2x3 auxiliary power cable is connected

If you map it to today’s PC-building terminology, this is essentially the familiar GPU 6-pin auxiliary power connector.

3. `PCIe 2x4`: 8-pin, `150W`, and backward-compatible with `2x3`

The 2x4 Auxiliary Power Connector corresponds to the more common GPU 8-pin connector, and Intel gives it a target power level of 150W.

There are two especially important design points here:

A board-side 2x4 receptacle can accept either a 2x4 plug or a 2x3 plug
The graphics card uses SENSE0 and SENSE1 to identify which type of cable is actually plugged in

Intel gives the following detection logic:

`SENSE1`	`SENSE0`	Meaning
Ground	Ground	A `2x4` plug is inserted, so the graphics card may draw `150W` from the auxiliary connector
Open	Ground	A `2x3` plug is inserted, so the graphics card may draw only `75W`
Ground	Open	Reserved
Open	Open	No auxiliary power cable is connected

So a board-side 8-pin is not simply “a 6-pin with two extra pins.” It also carries the power-identification logic.

4. `12V-2x6`: the new high-power connector, up to `600W`

With 12V-2x6, the positioning changes completely. Intel directly defines it as a 12V power connector for PCIe add-in cards that can deliver up to 600W.

The main points in the document include:

12V-2x6 is not compatible with 2x3 or 2x4
Its primary power-contact pitch is 3.0 mm
The contact pitch of 2x3 and 2x4 is larger at 4.2 mm
This connector uses 12 large contacts for power delivery, plus 4 smaller contacts for sideband signals

Its cable requirements are also stricter than those of older connectors:

Power and ground wires use 16 AWG
All 12 main power pins must be fully wired, with no missing conductors
Sideband signal wires use 28 AWG
The main power pins are rated at 9.2A/pin

The document also requires an H++ marking on the connector body to indicate support for 9.2A/pin or higher.

The image above is Figure 5-3 on Intel’s page, corresponding to the 12V-2x6 Cable Plug Connector.

This one is Figure 5-5, corresponding to the 12V-2x6 PCB Header. Looking at the two diagrams together, it becomes much easier to see that this is no longer the traditional 6-pin/8-pin connector form.

5. Why `12V-2x6` is not the same as the early `12VHPWR`

Intel includes a dedicated section in this guide called 12V-2x6 vs. 12VHPWR.

Its conclusion is very clear:

Early 12VHPWR has been deprecated
PCIe CEM 5.1 switched to 12V-2x6
The two look broadly similar, but the newer connector adds several reliability improvements

The core changes mainly fall into two groups.

The first is mechanical structure:

The main power pins are longer
The sideband pins are shorter

The goal is to let the main power pins make contact first and break contact last, while the sideband signals only connect after the main power pins have been inserted deeply enough.

The second group is updated SENSE0 / SENSE1 logic:

The 150W level now requires SENSE0 and SENSE1 to be shorted together
When both signals are in the Open-Open state, the new spec defines that as 0W
In other words, if the plug is not fully inserted, or not inserted at all, a compliant graphics card should not draw power from that cable

That is also one of the reasons 12V-2x6 is considered more conservative and more robust than the early 12VHPWR.

6. What do the four `12V-2x6` sideband signals do?

On the sideband-signal page, Intel defines four signals for 12V-2x6:

SENSE0, required
SENSE1, required
CARD_PWR_STABLE, optional
CARD_CBL_PRES#, required on the graphics-card side and optional on the power-supply side

1. `SENSE0 / SENSE1`

These two signals tell the graphics card what power level the cable and power supply currently allow.

Intel provides the following power table:

`SENSE0`	`SENSE1`	Initial allowed power at startup	Maximum sustained power after software configuration
Ground	Ground	`375W`	`600W`
Open	Ground	`225W`	`450W`
Ground	Open	`150W`	`300W`
Short	Short	`100W`	`150W`
Open	Open	`0W`	`0W`

The key is not memorizing the table, but understanding this: 12V-2x6 is no longer just a binary “power/no power” connector. Through sideband signals, it explicitly encodes multiple power tiers to the graphics card.

2. `CARD_PWR_STABLE`

This is an optional signal, and it behaves a lot like a graphics-card feedback version of Power Good.

Intel defines it this way:

When the graphics card’s local critical power rails are within normal range, this signal stays open/high impedance
When the graphics card detects that those local critical rails are out of range, it actively pulls the signal low
If this signal is implemented, the power-supply side should pull it up to +3.3V through 4.7 kOhm

Put simply, it gives the power supply an extra fault-awareness input.

3. `CARD_CBL_PRES#`

This signal is more about connection detection:

It lets the power supply know that the 12V-2x6 cable really is connected to the graphics card and seated properly
In a modular power-supply setup, it can also help confirm whether the PSU-side 12V-2x6 cable is fully inserted

Intel also specifically notes that:

The graphics-card side must implement the basic logic for this signal
The graphics-card side should pull it down to ground through 4.7 kOhm
Monitoring this signal on the power-supply side is optional

It is not used to determine the allowed power level. That role still belongs to SENSE0 / SENSE1.

7. How to think about the relationship between these three generations of connectors

From a PC-building and connector-recognition perspective, you can simplify them into three generations:

2x3: the old 6-pin, typically positioned at 75W
2x4: the old 8-pin, typically positioned at 150W, and backward-compatible with 2x3
12V-2x6: the new high-power connector, up to 600W

Going one step further:

2x3 / 2x4 still follow the traditional auxiliary power-connector model
12V-2x6 standardizes high-power delivery, insertion state, and sideband communication together
The point of 12V-2x6 is not just higher wattage, but also stricter insertion detection and clearer power-state encoding

Summary

From Intel’s ATX 3.0 design guide, PCIe auxiliary power connectors for graphics cards are already divided very clearly into three layers:

2x3 corresponds to 75W
2x4 corresponds to 150W
12V-2x6 is aimed at up to 600W

And the real difference between 12V-2x6 and the old 12VHPWR is not just the name or the appearance, but also:

Updated mechanical structure for the main power pins and sideband pins
Revised SENSE0 / SENSE1 encoding rules
The addition of the more conservative Open-Open = 0W state
More complete connection and power-state handling through CARD_PWR_STABLE and CARD_CBL_PRES#

If you are looking into high-power graphics cards, modular PSU cables, or simply trying to understand the relationship between 6-pin, 8-pin, and 12V-2x6, Intel’s official design guide already lays out the framework quite clearly.

Reference Links

Intel EDC: PCI-Express (PCIe*) Add-in Card Connectors (Recommended) https://edc.intel.com/content/www/us/en/design/ipla/software-development-platforms/client/platforms/alder-lake-desktop/atx-version-3-0-multi-rail-desktop-platform-power-supply-design-guide/2.1a/pci-express-pcie-add-in-card-connectors-recommended/
Intel EDC: PCIe* Add-in Card 12V-2x6 Auxiliary Power Connector Sideband Signals https://edc.intel.com/content/www/us/en/design/ipla/software-development-platforms/client/platforms/alder-lake-desktop/atx-version-3-0-multi-rail-desktop-platform-power-supply-design-guide/2.1a/pcie-add-in-card-12v-2x6-auxiliary-power-connector-sideband-signals/
Intel EDC: SENSE0 & SENSE1 (Required) https://edc.intel.com/content/www/us/en/design/ipla/software-development-platforms/client/platforms/alder-lake-desktop/atx-version-3-0-multi-rail-desktop-platform-power-supply-design-guide/2.1a/sense0-amp-sense1-required/
Intel EDC: CARD_PWR_STABLE (Optional) https://edc.intel.com/content/www/us/en/design/ipla/software-development-platforms/client/platforms/alder-lake-desktop/atx-version-3-0-multi-rail-desktop-platform-power-supply-design-guide/2.1a/card-pwr-stable-optional/
Intel EDC: CARD_CBL_PRES# (Optional in Power Supply) https://edc.intel.com/content/www/us/en/design/ipla/software-development-platforms/client/platforms/alder-lake-desktop/atx-version-3-0-multi-rail-desktop-platform-power-supply-design-guide/2.1a/card-cbl-pres-optional-in-power-supply/
Intel EDC: Sideband Signals DC Specifications (Required) https://edc.intel.com/content/www/us/en/design/ipla/software-development-platforms/client/platforms/alder-lake-desktop/atx-version-3-0-multi-rail-desktop-platform-power-supply-design-guide/2.1a/sideband-signals-dc-specifications-required/

PCIe on KnightLi Blog

How Intel's ATX 3.0 Design Guide Classifies PCIe Auxiliary Power Connectors for GPUs

1. The short version first

2. PCIe 2x3: the old 6-pin, defined here as 75W

3. PCIe 2x4: 8-pin, 150W, and backward-compatible with 2x3

4. 12V-2x6: the new high-power connector, up to 600W

5. Why 12V-2x6 is not the same as the early 12VHPWR

6. What do the four 12V-2x6 sideband signals do?

1. SENSE0 / SENSE1

2. CARD_PWR_STABLE

3. CARD_CBL_PRES#