Connecting Cables

Motherboard Cables

The latest ATX standard uses a 24-pin connector previously found on server-sized EPS power supplies, but most motherboards don't require all 24 pins. The below example shows how a 20-pin plug fit into a 24-pin socket; the wide latch is designed to work with either 20-pin or 24-pin plugs.

Reasons for 24-pin power include added amperage supplied to PCI Express slots compared to older interface standards. While most cards won't "overdraw" a 20-pin connector, graphics card makers have suggestions for minimum available power.

The 4-pin or 8-pin ATX 12V connector satisfies the electrical demands of the CPU. Formerly known as the "P4" power connector, Intel added it to supplement its inefficient Pentium 4 cores, but it was adapted to AMD motherboards as well. 8-pin versions are a later development meant to address phenomenally power-hungry Pentium-D and Prescott core Pentium 4 processors, but current AMD and Intel processors are efficient enough to once again work from 4 pins. Most 8-pin boards will work with both 8-pin and 4-pin power, as the connectors are cross-compatible.

Also seen in the photo above are a 4-pin CPU fan power connector, and the Front Panel Audio connector. 4-pin fans are designed to use a new pulse width modulation automatic speed control, but the connectors are once again cross-compatible with 3-pin fans. Check your motherboard manual for instructions on the Front Panel Audio connection.

The case's power switch and indicator light, reset switch, and hard drive light are usually connected at the motherboard's lower front corner. LEDs pass current in only one direction, and "positive" pins indicated by a "plus" sign below normally connect to the colored wire on each lead. A black or white lead wire usually indicates "negative" or ground state.

USB connectors have been standardized for several years. The missing pin location is blocked by most front-panel USB connectors to assure that the connector is polarized correctly. A reversed connection would damage the motherboard, so 4-pin, 8-pin, or single-row internal break-out cables require special care. The missing pin indicates the negative/ground end of the connector.