4 pin CONNECTOR at the computer
| Pin | Name | Description |
|---|---|---|
| 1 | -SP | -Speaker |
| 2 | key | Key |
| 3 | GND | Ground |
| 4 | +SP5V | +Speaker +5 VDC |
The PC speaker connector is a 4-pin keyed Berg-strip header used to drive the system’s internal piezoelectric or cone speaker. IBM first defined it as connector J19 in the PC AT Technical Reference (March 1984), specifying a data-out signal on pin 1, a physical keying blank on pin 2, ground on pin 3, and a +5 Vdc supply on pin 4. The ATX specification retained the same 0.1-inch-pitch layout and signal assignment, making it a de-facto standard across AT-class and ATX motherboards from the mid-1980s onwards. The speaker signal is a square wave generated by the system timer, gated through the programmable peripheral interface.
Signals
- -SP — speaker drive signal (square wave output from system timer via PPI port B)
- key — physical keying blank; no electrical signal present on this position
- GND — ground reference
- +SP5V — +5 Vdc supply for the speaker circuit
Notes
The connector uses a 2.54 mm (0.1 inch) pitch Berg-strip housing; pin 2 is physically absent (keyed) to prevent reversed insertion. The signal on pin 1 is a square wave typically in the range of a few hundred hertz to several kilohertz; no audio amplification is provided by the header itself. Many ATX motherboards bring this header out as part of a combined front-panel block using individual 1-pin or 2-pin jumper housings rather than a single 4-pin body.