40pin

40-pin refers to any electrical connector or integrated circuit package that has forty pins. In common use, this takes the form of a 2×20 header with a 0.1 inch (2.54 mm) pitch, allowing straightforward attachment of ribbon cables or female headers. Pin numbering typically runs along each side in alternating order, with a notch or key indicating pin 1.

Historically, the term is strongly associated with the 40-pin IDE (PATA) interface used on personal computers to connect hard drives and optical drives. This edge connector carries data, address, and control signals across a 40-conductor ribbon cable. The cable often has a marked red stripe to indicate pin 1, helping ensure correct orientation when installing devices.

Another prominent 40-pin form factor appears on many single-board computers, notably the Raspberry Pi, which uses a 40-pin GPIO header. This header provides power, ground, and a set of programmable I/O pins for general-purpose use, along with dedicated serial interfaces such as I2C, SPI, and UART.

DIP-40 packages are also common in integrated circuits, where the device is mounted in a dual-inline package with forty pins arranged in two rows. Such packages have been used for various microcontrollers, memory devices, and analog ICs.

Because pinouts and signaling vary by device, a 40-pin connector is not universally interchangeable. Users should consult device documentation to verify signal assignments, voltage levels, and orientation before connecting or replacing 40-pin cables and headers.