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 inches 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 and is normally used to connect an external port to header pins on a motherboard. This connector is typically used for USB, or Serial (DB9) ports.
This connector is typically used to add a DB25 Parallel Port interface. Most of today's motherboards do not have this type of connection.
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 68-pin socket internal connection is the same size and shape as the external MD68 pin interface used for SCSI devices and cables. However, the internal flat ribbon version does not use any thumbscrews or latch clips to hold the connector in place; it is held in solely by the friction of the connector and pins. The 68-pin flat ribbon connector is unique in that the connectors on the cable are male, and the interfaces on SCSI drives and host controllers are female. This connector is very commonly used for wide SCSI buses.
4-pin power (5.25 inch)
The common 5.25 inch 4-pin power connector is impossible to miss inside 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.
4-pin power (3.5 inch)
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.
ATX 20-pin power
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.
ATX 24-pin power
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.
The 3-pin Fan power connector is found on power supplies within a computer case. This connector provides power to cooling fans.
The 4-pin Fan power connector is found on motherboards within a computer case. This connector provides power to cooling fans and is typically used on the fan that cools the CPU. This connector uses the same power arrangement as the 3-pin connector, therefore, a 3-pin connector can be used on a 4-pin fan. The 4th pin is a sensor that allows the fan to be controlled for speed and may give the ability to turn the fan on or off. If you use a 3-pin connector in a 4-pin slot, you will not be able to control the fan as it will always be powered on.
6-pin PCI Express
The 6-pin PCI Express connector is found on some PCI Express graphics cards. This connector is used for auxiliary power.
4-pin Pentium® 4 power
The 4-pin Pentium 4 power connector is found on Pentium 4 motherboards. This connector delivers dedicated power to the CPU.
Serial ATA (SATA)
The Serial ATA or SATA connector is used as an interface for connecting a host bus adapter to a mass storage device or optical drive. This connector was designed to replace the older connectors, 34-pin, 40-pin, etc. This connection type is designed to communicate at much higher speeds than what were possible with the older connection styles. This connection is sometimes referred to as the SATA "L" due to the shape of the connector.
External Serial ATA (eSATA)
Similar to the standard SATA connector, the eSATA connector is shielded and designed to connect external mass storage devices or optical drives to an eSATA port. This connector is sometime referred to as the SATA "I" connector due to the shape of the connector.
Serial ATA (SATA) Power
The Serial ATA (SATA) Power connector has 15 pins and is slightly larger than the SATA data connector. One main advantage the SATA power connector provides over the 4 pin power connector is a pin that provides 3.3 V of power. Certain SATA drives have specific power requirements.
32-pin Serial Attached SCSI (SAS)
The 32-pin SAS connector is typically found on SAS controller cards. SAS technology is a replacement for SCSI and is typically used to connect hard disk drives in data center applications. However, this connector can be used to connect a SAS expander. This connector is also referred to as the SFF-8484 connector. In many cases the 32-pin connector is being replaced by the mini-SAS connectors due to mini-SAS' smaller form factor.
29-pin Serial Attached SCSI (SAS)
The 29-pin SAS connector is typically found on SAS drives. This connector does appear similar to the SATA data and power connection. However, this connector has 4 additional pins. This connector is also referred to as the SFF-8482 connector.