The motherboard is the main circuit board in any computer. Everything connects either directly or indirectly to the motherboard. It is truly the heart of the computer. The CPU and memory are installed directly on the motherboard. Disk drives connect to the motherboard by cables. The motherboard has external connections at the back that are accessible even when the computer’s case is closed up. These include the PS2 ports, USB ports, and audio jacks. The expansion slots (AGP, PCI Express, and PCI) are not themselves accessible from the back of the computer, but cards installed in them typically have externally accessible connections on the back.

The connections on the back edge of the motherboard are labeled above. These ports are accessible to the user when the computer's case is closed up.

PS2 Mouse and Keyboard Ports: Round connector consisting to 6 small pins used to connect a mouse or keyboard to the computer. Although the ports are physically identical, they are not interchangeable. When connecting PS2 mice and keyboards, just match the colors. Mice will have a light green plug and keyboards will have a purple plug. If you happen to have an older mouse or keyboard that don't follow the color coding rules, just assume that the mouse is on top and the keyboard is on bottom. No harm will come from mixing them up, but they won’t work in the wrong ports. Unplug the power cord from the computer for 15 seconds before connecting or disconnecting a PS2 mouse or keyboard to make sure the motherboard is completely off. PS2 mice and keyboards are being phased out but if your motherboard still has PS2 ports, using them will free up a USB port and PS2 tends to be more reliable than USB.

USB: Short for Universal Serial Bus. USB is designed to replace PS2, serial, and parallel ports with a single port that can be used for nearly any device you might want to connect to a PC. Mice, keyboards, printers, scanners, portable hard drives, flash drives, network adapters, headsets, Bluetooth adapters, memory card readers, and more are now commonly connected to a PC via its USB port. USB ports supply electricity to the device attached so low power devices can operate off the USB port's power. Devices with higher power needs, like scanners or printers, will still need to be plugged into the wall for power. Modern computers typically have anywhere from 4 to 10 USB ports divided between the back of the motherboard and the front of the case.

Serial Port: A virtually obsolete connector that was once used to connect devices to a PC. Modems, printers, and mice were the most common serial devices. This is a 9 pin serial port but 25 pin ports also exists. They look just like the parallel port above but are male (like the 9 pin serial) instead. Most motherboards no longer have serial ports.

Parallel Port: Most commonly called a printer port but it can be used to connect more than printers to a PC. In the days before USB ports, scanners, portable disk drives, even computer-to-computer data transfer cables were all made for parallel ports. Many motherboards no longer have parallel ports.

VGA: This is for connecting an analog monitor. Older CRT (big, heavy TV-like) monitors use the VGA port. This motherboard has VGA built-in so no additional cards are required to connect a monitor to the system. Every computer needs video capability. Video in this case refers not just to movies but to everything you see on your computer. Without video, you’d have no way of seeing and operating the computer.

Ethernet: Ethernet ports are used to connect a PC to a network. It can connect to an office network where the PC user needs to access files on other computers or a shared printer. It can also be used to connect to a cable or DSL modem for Internet access.

Audio: This motherboard has audio capability built-in so no separate sound card is required. The audio connectors are color coded as follow: Blue is line-in. Say you had a sound recording and editing program on your PC and you wanted to record from a cassette player, you’d connect the headphone jack of the cassette player to the blue line-in jack. The light green jack is the speaker output. Connect your speakers here. Newer motherboards have a black jack for rear speakers that are used in surround sound setups. In that case, the green jack is for the front speakers. The red jack is for a microphone.

 The internal connectors on the motherboard are labeled above. The computer's case must be opened to access these connectors.

PCI Slots: These are general purpose expansion slots. Many different kinds of devices and ports can be added to a PC by installing a PCI card. If you wanted better audio performance than the onboard audio offered, you could install a PCI audio card. If you ran out of USB ports, you could add a PCI card with additional USB ports. PCI cards with serial, parallel, or Ethernet ports can be installed to add those ports to motherboards which lack them built-in.

AGP Slot: This is where a dedicated video card is installed in the PC. If the motherboard didn’t have a VGA port built in, you’d have to install a video card or there would be nowhere to connect a monitor. The AGP slot is used only for video cards: no other type of card can use this slot. AGP slots are being phased out and replaced with a different kind of slot called PCI Express. PCI Express slots look similar to AGP slots but they are usually black and offer much better performance than AGP.

CMOS Battery: This is a simple coin cell battery that supplies enough power to the motherboard when its turned off to keep certain information alive. The date and time along with dozens of customizable options are stored on the motherboard and powered by this battery when the computer is turned off and unplugged.

IDE Ports: These ports are used to connect disk drives to the computer. Hard drives and optical drives (CD-ROM, DVD-ROM, CD-RW, or DVD-RW) are the most common drives connected to IDE ports. This motherboard has two IDE ports, each of which can host two drives. If more IDE devices must be connected to the computer, a PCI IDE card can be installed to give the computer more IDE ports. IDE ports are being phased out in favor of SATA ports. SATA is also used to connect hard drives and optical drives to a PC but the cables and connectors are different.

Floppy Port: Used to connect an internal floppy disk drive to a PC. It uses a cable and connector similar to IDE, but slightly narrower. Many motherboards no longer have internal floppy ports. If needed, a floppy drive can be connected to such systems via a USB port.

Power Supply Connectors: This is where the motherboard, CPU, memory, and any PCI or AGP cards installed get their electricity from the power supply. This motherboard has two connectors, both of which must be connected for proper operation.

Memory Slots: Memory (RAM) is installed in these slots. Memory comes on long, narrow boards called DIMMs. Memory is volatile meaning that its contents are erased when the system is rebooted or turned off. Nothing is permanently stored in memory.

CPU Socket: This is where the CPU connects to the motherboard. The rectangular black frame around the CPU socket is for holding the heat sink tightly to the CPU.