E189 · Source-scoped pinout variants

ATX 24-pin main power connector engineering reference

Intel ATX Version 3.0 main-power assignment; modular PSU-side wiring is explicitly outside this profile.

Open field note Source trail

Source checked · no independent review claimed · Fabrication approved: no

ATX 24-pin main-power logical assignment original orientation schematic — Original pinout diagram; read the exact variant and view below. Not to scale.

Contact count

24

PSU main-power cable plug / motherboard header interface

Mating boundary

Shape is not the verdict.

ATX main-power cable plug ↔ compatible ATX motherboard header

Orientation

How to read this profile

Logical table numbering from Intel Table 5-1. V37 does not assert left/right physical face orientation from the table; use the controlling connector drawing before probing or fabrication.

Source-scoped identification facts

Each value retains its exact example, role and measurement axis. Facts from different parts must not be combined into an invented component.

Documented examples; not a mating drawing or compatibility approval
Nominal contacts	24S197Documented position count only; V36 does not publish the signal/power assignment here.
Contact rows	2 (Source-described array; C189A); 2 (39-01-2240)S197 · S935Named source examples retain separate role, part, view and axis limits; values are not a universal family specification. V36 catalogue-expansion identification fact only; not independent technical approval, fabrication data, wiring instruction or end-to-end compatibility proof. 39-01-2240. Documented role: socket housing. Molexlimited-online-catalog notice recorded. No housing-only current rating used for completed ATX harness.; KeyingNo and PolarizedYes are separate manufacturerattributes;retained in context,not a newly observed keyshape.
Contact pitch	4.2 mm published contact centerline (39-01-2240)S935Named source examples retain separate role, part, view and axis limits; values are not a universal family specification. 39-01-2240. Documented role: socket housing. Molexlimited-online-catalog notice recorded. No housing-only current rating used for completed ATX harness.; KeyingNo and PolarizedYes are separate manufacturerattributes;retained in context,not a newly observed keyshape.
Connector role	plug; header; socket housing (39-01-2240)S197 · S214 · S935Named source examples retain separate role, part, view and axis limits; values are not a universal family specification. PSU main-power cable plug / motherboard header interface 39-01-2240. Documented role: socket housing. Molexlimited-online-catalog notice recorded. No housing-only current rating used for completed ATX harness.; KeyingNo and PolarizedYes are separate manufacturerattributes;retained in context,not a newly observed keyshape.
Coupling / latch	latch (Claim C189C); Positive mating lock;manufacturer separately lists polarized yes and keyed no (39-01-2240)S570 · S935Named source examples retain separate role, part, view and axis limits; values are not a universal family specification. V139 Source-scoped identification only. No complete cable assembly, universal mating, pin assignment, safe operating load, installation instruction or independent approval is established. 39-01-2240. Documented role: socket housing. Molexlimited-online-catalog notice recorded. No housing-only current rating used for completed ATX harness.; KeyingNo and PolarizedYes are separate manufacturerattributes;retained in context,not a newly observed keyshape.
Manufacturer	Molex (39-01-2240)S935Named source examples retain separate role, part, view and axis limits; values are not a universal family specification. 39-01-2240. Documented role: socket housing. Molexlimited-online-catalog notice recorded. No housing-only current rating used for completed ATX harness.; KeyingNo and PolarizedYes are separate manufacturerattributes;retained in context,not a newly observed keyshape.
Series	Mini-Fit Jr. (39-01-2240)S935Named source examples retain separate role, part, view and axis limits; values are not a universal family specification. 39-01-2240. Documented role: socket housing. Molexlimited-online-catalog notice recorded. No housing-only current rating used for completed ATX harness.; KeyingNo and PolarizedYes are separate manufacturerattributes;retained in context,not a newly observed keyshape.
Exact part / implementation	39-01-2240 (39-01-2240)S935Named source examples retain separate role, part, view and axis limits; values are not a universal family specification. 39-01-2240. Documented role: socket housing. Molexlimited-online-catalog notice recorded. No housing-only current rating used for completed ATX harness.; KeyingNo and PolarizedYes are separate manufacturerattributes;retained in context,not a newly observed keyshape.

Not recorded: Positions / cavity span, Populated contacts, Dimensions / axis, Contact gender / arrangement, Mounting, Keying / polarization, Shell / form, Recorded markings, View convention. Unknown fields stay unknown; illustrations supply no measurements or pin assignments.

Recorded variant and source limits

The normalized grid is not a physical face-view pin locator.
Do not apply this motherboard-side assignment to a modular PSU-side connector; those interfaces can be vendor-specific.
No fabrication tolerances or safe probing procedure are published.
Intel ATX v3 PSU main power cable connector (Molex 39-01-2240 or equivalent): Contact numbers per Table 5-1; Figure 5-2 is a pin-side view.
SSI 2008 dual-socket server/workstation PSU P1 baseboard connector: Contact numbers per Table 3.
MSI MAG B550 TOMAHAWK ATX_PWR1 board header: Board header; manual diagram labels corners 1, 12, 13, 24.
GIGABYTE B550 AORUS ELITE (AX) ATX board header: Board header; manual diagram labels corners 1, 12, 13, 24.
Intel rev 2.1a main-power cable harness: Numbered assignments only. The retrieved Intel section supplies a table but no numbered mating-face or wire-side drawing; spatial orientation is UNVERIFIED. Do not mirror these numbers onto an unidentified cable end.
MSI B550-A PRO ATX_PWR1: MSI p.34 board-connector drawing as printed: vertical layout, 12 upper left, 1 lower left, 24 upper right, 13 lower right. Not a cable rear view.

Report a correction to these facts →

Pins & wiring

Pinout

Choose the exact wiring. Pin numbers follow its stated view; a schematic does not establish physical positions. Check your exact device before wiring.

Dark pinout view

What the status labels mean

Confirmed: Recorded research passes agree within this variant; this is not independent human review or hardware validation.
Single source: Only one underlying document, or one pass, supports this assignment.
Device-specific: Supported for the named equipment or wiring only. Check your device’s manual.
Unverified: Missing or conflicting evidence. Do not wire from this row.
Not connected: The source explicitly says NC, no contact or no pin for this wiring.

Wiring variantIntel ATX v3 PSU main power cable connector (Molex 39-01-2240 or equ…

Intel ATX v3 PSU main power cable connector (Molex 39-01-2240 or equivalent)

View and evidence limits

Contact numbers per Table 5-1; Figure 5-2 is a pin-side view.

P189 ATX 24-pin — **Agree** on usable contact assignments — Both use Intel 336521 rev 2.1a: A's PDF and B's HTML are the **same document**, not independent corroboration. A also uses SSI, MSI MAG B550 TOMAHAWK and GIGABYTE B550; B uses MSI B550-A PRO. Pin 20 is reserved/NC: A records Intel's NC/no-wire state, while B conservatively marks its usable function unverified. Neither assigns a supply to it.
Earlier Intel ATX12V 1.x/2.x editions and the 20-pin-only plug were not retrieved from an official host in this pass; pin 20's historical -5 V use is stated only by the SSI note, not verified for any ATX edition here.

Schematic only · physical contact positions unconfirmed. Original drawing · not to scale. Scroll sideways if needed.

Intel ATX v3 PSU main power cable connector (Molex 39-01-2240 or equivalent) — source-scoped contact map
Pin	Signal	What it does	Status
1	+3.3V DC	Power connection (+3.3V DC). Check the specified supply.	Confirmed Sources
2	+3.3V DC	Power connection (+3.3V DC). Check the specified supply.	Confirmed Sources
3	COM	Ground reference and return.	Confirmed Sources
4	+5V DC	Power connection (+5V DC). Check the specified supply.	Confirmed Sources
5	COM	Ground reference and return.	Confirmed Sources
6	+5V DC	Power connection (+5V DC). Check the specified supply.	Confirmed Sources
7	COM	Ground reference and return.	Confirmed Sources
8	PWR_OK	Indicates that the supply outputs are ready.	Confirmed Sources
9	+5VSB	Power connection (+5VSB). Check the specified supply.	Confirmed Sources
10	+12V1 DC	Power connection (+12V1 DC). Check the specified supply.	Confirmed Sources
11	+12V1 DC	Power connection (+12V1 DC). Check the specified supply.	Confirmed Sources
12	+3.3V DC	Power connection (+3.3V DC). Check the specified supply.	Confirmed Sources
13	+3.3V DC [+3.3 V default sense]	Power connection (+3.3V DC [+3.3 V default sense]). Check the specified supply.	Confirmed Sources
14	-12V DC	Power connection (-12V DC). Check the specified supply.	Confirmed Sources
15	COM	Ground reference and return.	Confirmed Sources
16	PS_ON#	Requests that the power supply switch on.	Confirmed Sources
17	COM	Ground reference and return.	Confirmed Sources
18	COM	Ground reference and return.	Confirmed Sources
19	COM	Ground reference and return.	Confirmed Sources
20	Reserved	Not connected or absent in this named wiring.	Not connected Sources
21	+5V DC	Power connection (+5V DC). Check the specified supply.	Confirmed Sources
22	+5V DC	Power connection (+5V DC). Check the specified supply.	Confirmed Sources
23	+5V DC	Power connection (+5V DC). Check the specified supply.	Confirmed Sources
24	COM	Ground reference and return.	Confirmed Sources

Sources (5)

S755 · Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide
Document 336521, Revision 2.1a, November 2023 · Section 5.2.2.1, Table 5-1 Main Power Connector Pin-Out, printed p. 55
S756 · Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide
2.1a; web date 11/01/2023 · Mechanical > Connectors > DC Connectors > Main Power Connector — REQUIRED, Table 5-1: Main Power Connector Pin-Out
S757 · Micro-Star International (MSI) · B550-A PRO User Guide
Version 6.0, 2024/02, First release (Revision History, PDF p.59) · printed/PDF p.34, CPU_PWR1, ATX_PWR1: Power Connectors, ATX_PWR1, numbered drawing and Pin/Signal Name table
S758 · Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide
2.1a; web date 11/01/2023 · Electrical > Timing, Housekeeping and Control > PWR_OK — REQUIRED, opening paragraphs and Table 4-11
S759 · Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide
2.1a; web date 11/01/2023 · Electrical > Timing, Housekeeping and Control > PS_ON# — REQUIRED, opening paragraphs and Table 4-12

SSI 2008 dual-socket server/workstation PSU P1 baseboard connector

View and evidence limits

Contact numbers per Table 3.

P189 ATX 24-pin — **Agree** on usable contact assignments — Both use Intel 336521 rev 2.1a: A's PDF and B's HTML are the **same document**, not independent corroboration. A also uses SSI, MSI MAG B550 TOMAHAWK and GIGABYTE B550; B uses MSI B550-A PRO. Pin 20 is reserved/NC: A records Intel's NC/no-wire state, while B conservatively marks its usable function unverified. Neither assigns a supply to it.
Earlier Intel ATX12V 1.x/2.x editions and the 20-pin-only plug were not retrieved from an official host in this pass; pin 20's historical -5 V use is stated only by the SSI note, not verified for any ATX edition here.

Schematic only · physical contact positions unconfirmed. Original drawing · not to scale. Scroll sideways if needed.

SSI 2008 dual-socket server/workstation PSU P1 baseboard connector — source-scoped contact map
Pin	Signal	What it does	Status
1	+3.3 VDC	Power connection (+3.3 VDC). Check the specified supply.	Confirmed Sources
2	+3.3 VDC	Power connection (+3.3 VDC). Check the specified supply.	Confirmed Sources
3	COM	Ground reference and return.	Confirmed Sources
4	+5 VDC	Power connection (+5 VDC). Check the specified supply.	Confirmed Sources
5	COM	Ground reference and return.	Confirmed Sources
6	+5 VDC	Power connection (+5 VDC). Check the specified supply.	Confirmed Sources
7	COM	Ground reference and return.	Confirmed Sources
8	PWR OK	Indicates that the supply outputs are ready.	Confirmed Sources
9	5 VSB	Power connection (5 VSB). Check the specified supply.	Confirmed Sources
10	+12 V4	Power connection (+12 V4). Check the specified supply.	Single source Sources
11	+12 V4	Power connection (+12 V4). Check the specified supply.	Single source Sources
12	+3.3 VDC	Power connection (+3.3 VDC). Check the specified supply.	Confirmed Sources
13	+3.3 VDC	Power connection (+3.3 VDC). Check the specified supply.	Confirmed Sources
14	-12 VDC	Power connection (-12 VDC). Check the specified supply.	Confirmed Sources
15	COM	Ground reference and return.	Confirmed Sources
16	PS_ON	Requests that the power supply switch on.	Single source Sources
17	COM	Ground reference and return.	Confirmed Sources
18	COM	Ground reference and return.	Confirmed Sources
19	COM	Ground reference and return.	Confirmed Sources
20	Reserved (-5 V in ATX)	Not connected or absent in this named wiring.	Not connected Sources
21	+5 VDC	Power connection (+5 VDC). Check the specified supply.	Confirmed Sources
22	+5 VDC	Power connection (+5 VDC). Check the specified supply.	Confirmed Sources
23	+5 VDC	Power connection (+5 VDC). Check the specified supply.	Confirmed Sources
24	COM	Ground reference and return.	Confirmed Sources

Sources (4)

S760 · SSI Forum (archive hosted by SNIA) · Power Supply Design Guideline for 2008 Dual-Socket Servers and Workstations (A Server System Infrastructure Specification)
Version 1.2.1 (copyright 2008-2012 SSI Forum) · Section 4.2.1, Table 3 P1 Baseboard Power Connector, printed p. 10
S756 · Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide
2.1a; web date 11/01/2023 · Mechanical > Connectors > DC Connectors > Main Power Connector — REQUIRED, Table 5-1: Main Power Connector Pin-Out
S757 · Micro-Star International (MSI) · B550-A PRO User Guide
Version 6.0, 2024/02, First release (Revision History, PDF p.59) · printed/PDF p.34, CPU_PWR1, ATX_PWR1: Power Connectors, ATX_PWR1, numbered drawing and Pin/Signal Name table
S758 · Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide
2.1a; web date 11/01/2023 · Electrical > Timing, Housekeeping and Control > PWR_OK — REQUIRED, opening paragraphs and Table 4-11

MSI MAG B550 TOMAHAWK ATX_PWR1 board header

Device-specific wiring. Check your device’s manual before connecting or applying power.

View and evidence limits

Board header; manual diagram labels corners 1, 12, 13, 24.

P189 ATX 24-pin — **Agree** on usable contact assignments — Both use Intel 336521 rev 2.1a: A's PDF and B's HTML are the **same document**, not independent corroboration. A also uses SSI, MSI MAG B550 TOMAHAWK and GIGABYTE B550; B uses MSI B550-A PRO. Pin 20 is reserved/NC: A records Intel's NC/no-wire state, while B conservatively marks its usable function unverified. Neither assigns a supply to it.
Earlier Intel ATX12V 1.x/2.x editions and the 20-pin-only plug were not retrieved from an official host in this pass; pin 20's historical -5 V use is stated only by the SSI note, not verified for any ATX edition here.

Schematic only · physical contact positions unconfirmed. Original drawing · not to scale. Scroll sideways if needed.

MSI MAG B550 TOMAHAWK ATX_PWR1 board header — source-scoped contact map
Pin	Signal	What it does	Status
1	+3.3V	Power connection (+3.3V). Check the specified supply.	Device-specific Sources
2	+3.3V	Power connection (+3.3V). Check the specified supply.	Device-specific Sources
3	Ground	Ground reference and return.	Device-specific Sources
4	+5V	Power connection (+5V). Check the specified supply.	Device-specific Sources
5	Ground	Ground reference and return.	Device-specific Sources
6	+5V	Power connection (+5V). Check the specified supply.	Device-specific Sources
7	Ground	Ground reference and return.	Device-specific Sources
8	PWR OK	Indicates that the supply outputs are ready.	Device-specific Sources
9	5VSB	Power connection (5VSB). Check the specified supply.	Device-specific Sources
10	+12V	Power connection (+12V). Check the specified supply.	Device-specific Sources
11	+12V	Power connection (+12V). Check the specified supply.	Device-specific Sources
12	+3.3V	Power connection (+3.3V). Check the specified supply.	Device-specific Sources
13	+3.3V	Power connection (+3.3V). Check the specified supply.	Device-specific Sources
14	-12V	Power connection (-12V). Check the specified supply.	Device-specific Sources
15	Ground	Ground reference and return.	Device-specific Sources
16	PS-ON#	Requests that the power supply switch on.	Device-specific Sources
17	Ground	Ground reference and return.	Device-specific Sources
18	Ground	Ground reference and return.	Device-specific Sources
19	Ground	Ground reference and return.	Device-specific Sources
20	Res	Control, detection or configuration connection; check the source and device.	Device-specific Sources
21	+5V	Power connection (+5V). Check the specified supply.	Device-specific Sources
22	+5V	Power connection (+5V). Check the specified supply.	Device-specific Sources
23	+5V	Power connection (+5V). Check the specified supply.	Device-specific Sources
24	Ground	Ground reference and return.	Device-specific Sources

Sources (1)

S761 · Micro-Star International (MSI) · MAG B550 TOMAHAWK Motherboard User Guide (multilingual)
No revision printed; PDF creation date 2023-12-26 (file MAGB550TOMAHAWK.pdf) · English section, Overview of Components, 'CPU_PWR1, ATX_PWR1: Power Connectors', ATX_PWR1 table, printed p. 20

GIGABYTE B550 AORUS ELITE (AX) ATX board header

Device-specific wiring. Check your device’s manual before connecting or applying power.

View and evidence limits

Board header; manual diagram labels corners 1, 12, 13, 24.

P189 ATX 24-pin — **Agree** on usable contact assignments — Both use Intel 336521 rev 2.1a: A's PDF and B's HTML are the **same document**, not independent corroboration. A also uses SSI, MSI MAG B550 TOMAHAWK and GIGABYTE B550; B uses MSI B550-A PRO. Pin 20 is reserved/NC: A records Intel's NC/no-wire state, while B conservatively marks its usable function unverified. Neither assigns a supply to it.
Earlier Intel ATX12V 1.x/2.x editions and the 20-pin-only plug were not retrieved from an official host in this pass; pin 20's historical -5 V use is stated only by the SSI note, not verified for any ATX edition here.

Schematic only · physical contact positions unconfirmed. Original drawing · not to scale. Scroll sideways if needed.

GIGABYTE B550 AORUS ELITE (AX) ATX board header — source-scoped contact map
Pin	Signal	What it does	Status
1	3.3V	Power connection (3.3V). Check the specified supply.	Device-specific Sources
2	3.3V	Power connection (3.3V). Check the specified supply.	Device-specific Sources
3	GND	Ground reference and return.	Device-specific Sources
4	+5V	Power connection (+5V). Check the specified supply.	Device-specific Sources
5	GND	Ground reference and return.	Device-specific Sources
6	+5V	Power connection (+5V). Check the specified supply.	Device-specific Sources
7	GND	Ground reference and return.	Device-specific Sources
8	Power Good	Indicates that the supply outputs are ready.	Device-specific Sources
9	5VSB (stand by +5V)	Power connection (5VSB (stand by +5V)). Check the specified supply.	Device-specific Sources
10	+12V	Power connection (+12V). Check the specified supply.	Device-specific Sources
11	+12V (Only for 2x12-pin ATX)	Power connection (+12V (Only for 2x12-pin ATX)). Check the specified supply.	Device-specific Sources
12	3.3V (Only for 2x12-pin ATX)	Power connection (3.3V (Only for 2x12-pin ATX)). Check the specified supply.	Device-specific Sources
13	3.3V	Power connection (3.3V). Check the specified supply.	Device-specific Sources
14	-12V	Power connection (-12V). Check the specified supply.	Device-specific Sources
15	GND	Ground reference and return.	Device-specific Sources
16	PS_ON (soft On/Off)	Requests that the power supply switch on.	Device-specific Sources
17	GND	Ground reference and return.	Device-specific Sources
18	GND	Ground reference and return.	Device-specific Sources
19	GND	Ground reference and return.	Device-specific Sources
20	NC	Not connected or absent in this named wiring.	Not connected Sources
21	+5V	Power connection (+5V). Check the specified supply.	Device-specific Sources
22	+5V	Power connection (+5V). Check the specified supply.	Device-specific Sources
23	+5V (Only for 2x12-pin ATX)	Power connection (+5V (Only for 2x12-pin ATX)). Check the specified supply.	Device-specific Sources
24	GND (Only for 2x12-pin ATX)	Ground reference and return.	Device-specific Sources

Sources (1)

S762 · GIGA-BYTE Technology · B550 AORUS ELITE / B550 AORUS ELITE AX User's Manual
Rev. 1002, 12ME-B55AELT-1002R (copyright 2020) · Chapter 1, item 1/2) ATX_12V/ATX, 'ATX:' pin table, printed p. 15

Intel rev 2.1a main-power cable harness

View and evidence limits

Numbered assignments only. The retrieved Intel section supplies a table but no numbered mating-face or wire-side drawing; spatial orientation is UNVERIFIED. Do not mirror these numbers onto an unidentified cable end.

P189 ATX 24-pin — **Agree** on usable contact assignments — Both use Intel 336521 rev 2.1a: A's PDF and B's HTML are the **same document**, not independent corroboration. A also uses SSI, MSI MAG B550 TOMAHAWK and GIGABYTE B550; B uses MSI B550-A PRO. Pin 20 is reserved/NC: A records Intel's NC/no-wire state, while B conservatively marks its usable function unverified. Neither assigns a supply to it.
Intel names cable housing Molex 39-01-2240 and motherboard mate 44206-0007. Pin 13 combines power and the default sense wire.
Pin 20 is Reserved, with NC in the Color column. This pass does not infer a usable function from that notation.
Pin 20 remains unverified as a usable function in both variants. Intel table-only spatial orientation and proprietary modular PSU endpoint pinouts are unverified.

Schematic only · physical contact positions unconfirmed. Original drawing · not to scale. Scroll sideways if needed.

Intel rev 2.1a main-power cable harness — source-scoped contact map
Pin	Signal	What it does	Status
1	+3.3V DC	Power connection (+3.3V DC). Check the specified supply.	Confirmed Sources
2	+3.3V DC	Power connection (+3.3V DC). Check the specified supply.	Confirmed Sources
3	COM	Ground reference and return.	Confirmed Sources
4	+5V DC	Power connection (+5V DC). Check the specified supply.	Confirmed Sources
5	COM	Ground reference and return.	Confirmed Sources
6	+5V DC	Power connection (+5V DC). Check the specified supply.	Confirmed Sources
7	COM	Ground reference and return.	Confirmed Sources
8	PWR_OK	Indicates that the supply outputs are ready.	Confirmed Sources
9	+5VSB	Power connection (+5VSB). Check the specified supply.	Confirmed Sources
10	+12V1 DC	Power connection (+12V1 DC). Check the specified supply.	Confirmed Sources
11	+12V1 DC	Power connection (+12V1 DC). Check the specified supply.	Confirmed Sources
12	+3.3V DC	Power connection (+3.3V DC). Check the specified supply.	Confirmed Sources
13	+3.3V DC [+3.3 V default sense]	Power connection (+3.3V DC [+3.3 V default sense]). Check the specified supply.	Confirmed Sources
14	-12V DC	Power connection (-12V DC). Check the specified supply.	Confirmed Sources
15	COM	Ground reference and return.	Confirmed Sources
16	PS_ON#	Requests that the power supply switch on.	Confirmed Sources
17	COM	Ground reference and return.	Confirmed Sources
18	COM	Ground reference and return.	Confirmed Sources
19	COM	Ground reference and return.	Confirmed Sources
20	Not confirmed	No settled assignment. Do not wire from this row.	Unverified Sources
21	+5V DC	Power connection (+5V DC). Check the specified supply.	Confirmed Sources
22	+5V DC	Power connection (+5V DC). Check the specified supply.	Confirmed Sources
23	+5V DC	Power connection (+5V DC). Check the specified supply.	Confirmed Sources
24	COM	Ground reference and return.	Confirmed Sources

Sources (7)

S756 · Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide
2.1a; web date 11/01/2023 · Mechanical > Connectors > DC Connectors > Main Power Connector — REQUIRED, Table 5-1: Main Power Connector Pin-Out
S755 · Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide
Document 336521, Revision 2.1a, November 2023 · Section 5.2.2.1, Table 5-1 Main Power Connector Pin-Out, printed p. 55
S760 · SSI Forum (archive hosted by SNIA) · Power Supply Design Guideline for 2008 Dual-Socket Servers and Workstations (A Server System Infrastructure Specification)
Version 1.2.1 (copyright 2008-2012 SSI Forum) · Section 4.2.1, Table 3 P1 Baseboard Power Connector, printed p. 10
S761 · Micro-Star International (MSI) · MAG B550 TOMAHAWK Motherboard User Guide (multilingual)
No revision printed; PDF creation date 2023-12-26 (file MAGB550TOMAHAWK.pdf) · English section, Overview of Components, 'CPU_PWR1, ATX_PWR1: Power Connectors', ATX_PWR1 table, printed p. 20
S762 · GIGA-BYTE Technology · B550 AORUS ELITE / B550 AORUS ELITE AX User's Manual
Rev. 1002, 12ME-B55AELT-1002R (copyright 2020) · Chapter 1, item 1/2) ATX_12V/ATX, 'ATX:' pin table, printed p. 15
S758 · Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide
2.1a; web date 11/01/2023 · Electrical > Timing, Housekeeping and Control > PWR_OK — REQUIRED, opening paragraphs and Table 4-11
S759 · Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide
2.1a; web date 11/01/2023 · Electrical > Timing, Housekeeping and Control > PS_ON# — REQUIRED, opening paragraphs and Table 4-12

MSI B550-A PRO ATX_PWR1

Device-specific wiring. Check your device’s manual before connecting or applying power.

View and evidence limits

MSI p.34 board-connector drawing as printed: vertical layout, 12 upper left, 1 lower left, 24 upper right, 13 lower right. Not a cable rear view.

P189 ATX 24-pin — **Agree** on usable contact assignments — Both use Intel 336521 rev 2.1a: A's PDF and B's HTML are the **same document**, not independent corroboration. A also uses SSI, MSI MAG B550 TOMAHAWK and GIGABYTE B550; B uses MSI B550-A PRO. Pin 20 is reserved/NC: A records Intel's NC/no-wire state, while B conservatively marks its usable function unverified. Neither assigns a supply to it.
MSI does not identify a pin-13 sense function; its table is retained separately.
Pin 20 remains unverified as a usable function in both variants. Intel table-only spatial orientation and proprietary modular PSU endpoint pinouts are unverified.

Schematic only · physical contact positions unconfirmed. Original drawing · not to scale. Scroll sideways if needed.

MSI B550-A PRO ATX_PWR1 — source-scoped contact map
Pin	Signal	What it does	Status
1	+3.3V	Power connection (+3.3V). Check the specified supply.	Device-specific Sources
2	+3.3V	Power connection (+3.3V). Check the specified supply.	Device-specific Sources
3	Ground	Ground reference and return.	Device-specific Sources
4	+5V	Power connection (+5V). Check the specified supply.	Device-specific Sources
5	Ground	Ground reference and return.	Device-specific Sources
6	+5V	Power connection (+5V). Check the specified supply.	Device-specific Sources
7	Ground	Ground reference and return.	Device-specific Sources
8	PWR OK	Indicates that the supply outputs are ready.	Device-specific Sources
9	5VSB	Power connection (5VSB). Check the specified supply.	Device-specific Sources
10	+12V	Power connection (+12V). Check the specified supply.	Device-specific Sources
11	+12V	Power connection (+12V). Check the specified supply.	Device-specific Sources
12	+3.3V	Power connection (+3.3V). Check the specified supply.	Device-specific Sources
13	+3.3V	Power connection (+3.3V). Check the specified supply.	Device-specific Sources
14	-12V	Power connection (-12V). Check the specified supply.	Device-specific Sources
15	Ground	Ground reference and return.	Device-specific Sources
16	PS-ON#	Requests that the power supply switch on.	Device-specific Sources
17	Ground	Ground reference and return.	Device-specific Sources
18	Ground	Ground reference and return.	Device-specific Sources
19	Ground	Ground reference and return.	Device-specific Sources
20	Not confirmed	No settled assignment. Do not wire from this row.	Unverified Sources
21	+5V	Power connection (+5V). Check the specified supply.	Device-specific Sources
22	+5V	Power connection (+5V). Check the specified supply.	Device-specific Sources
23	+5V	Power connection (+5V). Check the specified supply.	Device-specific Sources
24	Ground	Ground reference and return.	Device-specific Sources

Sources (3)

S757 · Micro-Star International (MSI) · B550-A PRO User Guide
Version 6.0, 2024/02, First release (Revision History, PDF p.59) · printed/PDF p.34, CPU_PWR1, ATX_PWR1: Power Connectors, ATX_PWR1, numbered drawing and Pin/Signal Name table
S758 · Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide
2.1a; web date 11/01/2023 · Electrical > Timing, Housekeeping and Control > PWR_OK — REQUIRED, opening paragraphs and Table 4-11
S759 · Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide
2.1a; web date 11/01/2023 · Electrical > Timing, Housekeeping and Control > PS_ON# — REQUIRED, opening paragraphs and Table 4-12

Unknowns stay unknown.

The normalized grid is not a physical face-view pin locator.
Do not apply this motherboard-side assignment to a modular PSU-side connector; those interfaces can be vendor-specific.
No fabrication tolerances or safe probing procedure are published.

Your next step

Use the detail without guessing past its limits.

Read the connector field note Recognition clues and practical checks.Work through a connection Keep exact equipment and cable requirements separate.

Source trail

Claims and sources

C189Asource checked

Intel documents the ATX main power connector as a 24-pin / 2x12 connector interface in the cited design guide.

Intel · ATX Version 3.0 — Main Power Connector (Required) ↗
Main power connector section · Identification/reference scope only. V36 does not convert this source into a universal pinout, fabrication drawing, electrical approval or end-to-end compatibility verdict.

C189Bsource checked

Intel ATX Version 3.0 Table 5-1 assigns the 24 main-power positions as: 1 +3.3V, 2 +3.3V, 3 COM, 4 +5V, 5 COM, 6 +5V, 7 COM, 8 PWR_OK, 9 +5VSB, 10 +12V1, 11 +12V1, 12 +3.3V, 13 +3.3V/default sense, 14 -12V, 15 COM, 16 PS_ON#, 17 COM, 18 COM, 19 COM, 20 reserved/NC, 21 +5V, 22 +5V, 23 +5V, 24 COM.

Intel · ATX Version 3.0 — Main Power Connector pin-out ↗
Table 5-1 Main Power Connector Pin-Out · Logical assignment table only. V37 does not treat the normalized schematic as a mating-face drawing, fabrication drawing, cable-construction approval or replacement/repair instruction.

C805Wsource checked

Intel ATX v3 PSU main power cable connector (Molex 39-01-2240 or equivalent): original contact normalization. Statuses distinguish comparison agreement, source limits and named-device wiring.

Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide ↗
Revision history entry for 2.1 (printed p. 13): 12VHPWR renamed 12V-2x6 throughout, 'Cable Plug' side unchanged; Section 5.2.2.4.3 'Special Note on 12V-2x6 vs. 12VHPWR connectors' (printed p. 61); Table 5-7 (printed p. 66); Section 5.2.2.1, Table 5-1 Main Power Connector Pin-Out, printed p. 55; Section 5.2.2.2 Peripheral Connectors (AMP 1-480424-0 or Molex 15-24-4048), Table 5-2 Peripheral Connector Pin-out, printed pp. 55-56; Section 5.2.2.3 Floppy Drive Connector - Do Not Include (For Historical Reference Only), AMP 171822-4, Table 5-3 Floppy Connector Pin-out, printed p. 56; Section 5.2.2.4.1, Table 5-4 PCIe 2x3 Auxiliary Power Connector Pin Assignment (75 watts) and note 2, printed p. 57; Section 5.2.2.4.2, Table 5-5 PCIe 2x4 Auxiliary Power Connector Pin Assignment (150 Watts) and Table 5-6 Sense Pin Decoding, printed p. 58; Section 5.2.2.4.3, Table 5-7 PCIe 12V-2x6 Auxiliary Power Connector Pin Assignment (600 watts), printed p. 66; sideband definitions Section 3.3 and Table 3-6, printed pp. 29-32; Section 5.2.2.5, Table 5-9 +12 V Power 8 pin Connector Pin-Out, printed p. 67 · Source scope and unresolved evidence are preserved in the engineering variant.

Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide ↗
Mechanical > Connectors > DC Connectors > Main Power Connector — REQUIRED, Table 5-1: Main Power Connector Pin-Out · Source scope and unresolved evidence are preserved in the engineering variant.

Micro-Star International (MSI) · B550-A PRO User Guide ↗
printed/PDF p.33, JAUD1: Front Audio Connector, numbered drawing and Pin/Signal Name table; printed/PDF p.34, CPU_PWR1, ATX_PWR1: Power Connectors, ATX_PWR1, numbered drawing and Pin/Signal Name table; printed/PDF p.34, CPU_PWR1, ATX_PWR1: Power Connectors, CPU_PWR1, numbered drawing and Pin/Signal Name table; printed/PDF p.37, JUSB1~2: USB 2.0 Connectors, numbered drawing and Pin/Signal Name table; printed/PDF p.38, CPU_FAN1, PUMP_FAN1, SYS_FAN1~6: Fan Connectors, PWM Mode and DC Mode pin definition tables and mode explanation, numbered drawing and Pin/Signal Name table; printed/PDF p.40, JRGB1: RGB LED connector, numbered drawing and Pin/Signal Name table; printed/PDF p.41, JRAINBOW1~2: Addressable RGB LED connectors, numbered drawing and Pin/Signal Name table · Source scope and unresolved evidence are preserved in the engineering variant.

Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide ↗
Electrical > Timing, Housekeeping and Control > PWR_OK — REQUIRED, opening paragraphs and Table 4-11 · Source scope and unresolved evidence are preserved in the engineering variant.

Intel Corporation · ATX Version 3 Multi Rail Desktop Platform Power Supply Design Guide ↗
Electrical > Timing, Housekeeping and Control > PS_ON# — REQUIRED, opening paragraphs and Table 4-12 · Source scope and unresolved evidence are preserved in the engineering variant.

C805Xsource checked

SSI 2008 dual-socket server/workstation PSU P1 baseboard connector: original contact normalization. Statuses distinguish comparison agreement, source limits and named-device wiring.

SSI Forum (archive hosted by SNIA) · Power Supply Design Guideline for 2008 Dual-Socket Servers and Workstations (A Server System Infrastructure Specification) ↗
Section 4.2.1, Table 3 P1 Baseboard Power Connector, printed p. 10; Section 4.2.2, Table 4 Processor 0 / memory power Connector, printed p. 12; Section 4.2.2, Table 5 Processor 1 / memory power Connector, printed p. 12; Section 4.2.4, Table 7 Peripheral Power Connectors (Amp 1-480424-0), printed p. 13; Section 4.2.5, Table 8 Floppy Power Connector (Amp 171822-4), printed p. 13; Section 4.2.8, Table 11 PCI Express Graphic Card Power Connector(s), printed p. 15 · Source scope and unresolved evidence are preserved in the engineering variant.

C805Ysource checked

MSI MAG B550 TOMAHAWK ATX_PWR1 board header: original contact normalization. Statuses distinguish comparison agreement, source limits and named-device wiring.

Micro-Star International (MSI) · MAG B550 TOMAHAWK Motherboard User Guide (multilingual) ↗
English section, 'CPU_FAN1, PUMP_FAN1, SYS_FAN1~6: Fan Connectors', PWM Mode and DC Mode pin definition tables, printed p. 23; English section, 'CPU_PWR1, ATX_PWR1: Power Connectors', CPU_PWR1 table, printed p. 20; English section, 'JAUD1: Front Audio Connector' table, printed p. 19; English section, 'JRAINBOW1~2: Addressable RGB LED connectors' table, printed p. 27; English section, 'JRGB1~2: RGB LED connectors' table, printed p. 26; English section, 'JUSB1~2: USB 2.0 Connectors' table, printed p. 22; English section, Overview of Components, 'CPU_PWR1, ATX_PWR1: Power Connectors', ATX_PWR1 table, printed p. 20 · Source scope and unresolved evidence are preserved in the engineering variant.

C805Zsource checked

GIGABYTE B550 AORUS ELITE (AX) ATX board header: original contact normalization. Statuses distinguish comparison agreement, source limits and named-device wiring.

GIGA-BYTE Technology · B550 AORUS ELITE / B550 AORUS ELITE AX User's Manual ↗
Chapter 1, item 1/2) ATX_12V/ATX, 'ATX:' pin table, printed p. 15; Chapter 1, item 1/2) ATX_12V/ATX, 'ATX_12V:' pin table, printed p. 15; Chapter 1, item 12) F_AUDIO (Front Panel Audio Header), High Definition audio table, printed p. 19; Chapter 1, item 14) F_USB1/F_USB2 (USB 2.0/1.1 Headers) table, printed p. 20; Chapter 1, item 3/4) CPU_FAN/SYS_FAN1/2/3 (Fan Headers) pin table, printed p. 15; item 5) CPU_OPT, printed p. 16; Chapter 1, item 7) D_LED1/D_LED2 (Addressable LED Strip Headers), printed p. 16; Chapter 1, item 8) LED_C1/LED_C2 (RGB LED Strip Headers), printed p. 17; item 6) LED_CPU, printed p. 16 · Source scope and unresolved evidence are preserved in the engineering variant.

C806Asource checked

Intel rev 2.1a main-power cable harness: original contact normalization. Statuses distinguish comparison agreement, source limits and named-device wiring.

C806Bsource checked

MSI B550-A PRO ATX_PWR1: original contact normalization. Statuses distinguish comparison agreement, source limits and named-device wiring.

10 source records support this profile. No independent engineering review or hardware validation is claimed.

Evidence behind this page

Scope first. Source second. Approval separate.

10 linked sources · 8 scoped claims · 0 sources with inspection/access flags.

Page scope: Original V37 logical-assignment schematic; not to scale and not a mating-face or manufacturing drawing.

Assessment 2026-10-22 · earliest scheduled source review 2027-01-03. This is a recorded-date assessment, not a live source check. Page-level independent review is not established by this panel.

Inspect 10 source scopes, access limits and dates

S197 · ATX Version 3.0 — Main Power Connector (Required)

Intel · Manufacturer / product-owner domain · inspected 2026-10-05 · due 2027-01-03

Within inspection window

Scoped support: Identifies the ATX main power connector as a 24-pin / 2x12 Mini-Fit Jr.-family interface in the documented ATX design guide.

Not established / limitations: Identification/reference scope only. V36 does not convert this source into a universal pinout, fabrication drawing, electrical approval or end-to-end compatibility verdict.

Locator: Main power connector section

S214 · ATX Version 3.0 — Main Power Connector pin-out

Intel · Manufacturer / product-owner domain · inspected 2026-10-05 · due 2027-01-03

Within inspection window

Scoped support: Engineering-sidecar source for the 24-position ATX main-power logical pin assignments and the documented 24-pin Mini-Fit Jr.-family connector reference.

Not established / limitations: Logical assignment table only. V37 does not treat the normalized schematic as a mating-face drawing, fabrication drawing, cable-construction approval or replacement/repair instruction.

Locator: Table 5-1 Main Power Connector Pin-Out