About Internal

Internal connectors are found inside a computer case. There are two primary types of connectors found internally: socket connectors and power connectors. Socket connectors are designed for use with flat ribbon cable, and are generally used to transfer data among devices. A socket connector mates with pins arranged into a header. Usually a header is built onto a piece of circuit board, or integrated into an electronic device. Socket connections are held in place by the friction of the pins. Most socket/header interfaces are built to similar dimensions; header pins are 0.025 inches in width, and spaced 0.10 inch apart. Power connectors are used to supply and distribute power to internal devices inside the computer. They normally use the friction of the connector bodies to stay in place.

This connector has two rows of five pins; it is normally used as part of a serial I/O cable. It plugs into a motherboard header to add a DB9 or DB25 serial port to a computer.

The 26-pin socket connector is used on older motherboards to provide a DB25 parallel port interface. Most of today’s motherboards have parallel ports built into them, or else omit the parallel port completely.

34-pin sockets are used for floppy drive cables. The floppy controller on a motherboard is a 34-pin header, as are the connections on 3.5-inch floppy drives. “Antique” 5.25-inch floppy drives used a card-edge connection to interface to the floppy cable, so many floppy cables will come with both socket and card-edge connectors. For many of today’s computers, floppy drives are no longer standard equipment.

This interface is still in wide use. It is found on IDE/ATA hard drives, optical drives, and tape drives. Many motherboards come with a pair of 40-pin controllers (described as primary and secondary). Each controller can handle one or two drives, so most standard PCs can have a maximum of four IDE drives. A few years ago, the IDE/ATA standard for hard drives was improved, and a new cable was specified. This new standard is referenced by many names—Ultra ATA, Ultra-DMA, Ultra-66/100/133, etc. Ultra ATA hard drive cables use an 80-conductor ribbon cable, although the same 40-pin socket/header interface is still used.

50-pin socket connectors are used for basic internal SCSI buses. The connector looks identical to a 40-pin IDE interface, only with more pins. The 50-pin interface is used for older, narrow SCSI buses.

The HD68 pin internal connection is the same size and shape as the HD68 pin interface used for external SCSI devices and cables. However, the internal flat-ribbon version does not use any thumbscrews or latchclips to hold the connector in place; it is held in solely by the friction of the connector and pins. The HD68 flat ribbon connector is unique in that the connectors on the cable itself are male, and the interfaces on SCSI drives and host controllers are female. This connector is very commonly used for wide SCSI buses.

The common 5.25-inch 4-pin power connector is impossible to miss on the inside of a PC case. A computer’s power supply normally provides several of these connectors, which mate to male interfaces on hard drives, CD/DVD drives, and other internal devices. Because these drives often have a 5.25-inch form factor, the power connector itself became known as a “5.25” connector. The plug is also commonly referenced as a “Molex” connection, after the well-known connector manufacturer. The connector is typically white in color, and made from hard nylon or similar plastic material.

A less common 4-pin power connector is the 3.5-inch plug. This connector is smaller in size than the 5.25-inch, and it is not as widely used. It can be found mainly on 3.5-inch floppy disk drives.

This is a 20-pin interface that supplies power to a computer’s motherboard. It has two rows of 10 pins, with a locking tab that holds it firmly in place after connection.

Newer computers with ATX-form factor motherboards use a 24-pin power connector. The newer, larger connector eliminates the -5V rail, and adds additional +3.3V and +12V rails.