IBM Personal Computer AT (1984)

AT Power Supply P8 and P9 Connector Pinout (IBM PC/AT)

Before ATX, a PC power supply fed the motherboard through two identical 6-pin plugs, P8 and P9, side by side on one 12-pin header. Select a contact to see its role.

Before you wire

  • P8 and P9 are not keyed against swapping. Fit them so that the four ground contacts, P8 pins 5–6 and P9 pins 1–2, are next to each other in the middle; a swapped pair puts the wrong voltages on the board.
  • The −5 V and −12 V rails served ISA-era chips and serial ports; later ATX supplies dropped −5 V.

Pin assignment

Pin 1: Power good1Pin 2: +5V2Pin 3: +12V3Pin 4: -12V4Pin 5: GND5Pin 6: GND6Pin 7: GND7Pin 8: GND8Pin 9: -5V9Pin 10: +5V10Pin 11: +5V11Pin 12: +5V12Pin 1: Power good1Pin 2: +5V2Pin 3: +12V3Pin 4: -12V4Pin 5: GND5Pin 6: GND6Pin 7: GND7Pin 8: GND8Pin 9: -5V9Pin 10: +5V10Pin 11: +5V11Pin 12: +5V12
  • Control
  • Power
  • Ground

Schematic face view, not to scale · numbering per IBM Personal Computer AT (1984)

Pin assignment of AT Power Supply P8/P9 Motherboard Connectors
PinSignalFunctionStatus
Power goodP8 pin 1: Power good, tells the motherboard that the supply voltages are stableStandard
+5VP8 pin 2: +5 VDCStandard
+12VP8 pin 3: +12 VDCStandard
-12VP8 pin 4: −12 VDCStandard
GNDP8 pin 5: groundStandard
GNDP8 pin 6: groundStandard
GNDP9 pin 1: groundStandard
GNDP9 pin 2: groundStandard
-5VP9 pin 3: −5 VDCStandard
+5VP9 pin 4: +5 VDCStandard
+5VP9 pin 5: +5 VDCStandard
+5VP9 pin 6: +5 VDCStandard

Pin details

Select a pin on the diagram or table for full details.

Pin details

About this connector

Pair of 6-contact AT power plugs, P8 and P9, carrying Power good, +5 V, +12 V, −12 V, −5 V and ground to IBM PC/AT-style motherboards.

Notes

  • Positions 1 to 6 are P8 pins 1 to 6 and positions 7 to 12 are P9 pins 1 to 6, in the order the two plugs sit on the motherboard header.
  • Pin assignments follow the IBM PC/AT Technical Reference (March 1984), page 1-58.

Common use cases

  • IBM PC/AT, Baby-AT and LPX motherboards, from 1984 to the late 1990s

Specifications

Standard
Two 6-position plugs (P8 + P9) on one 12-position header
Positions
12

Primary sources

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