The motherboard is the most important and intricate piece of hardware inside a computer. When putting together a computer, the first two decisions to make are usually on which motherboard and processor combo. Everything else that you add to a computer will be based on these pieces of hardware. When choosing a motherboard, there are a few things to look at. Pay close attention to the motherboards form factor, number of expansion slots, processor socket, chipset, buses, and onboard components. You will want to choose a motherboard that fits your needs. Example, if you are putting together a home file server and will need to hook up 5 hard drives or SSD’s, you will need a motherboard with enough SATA connectors to accommodate the number of drives you have as well as a couple extra SATA connectors for your optical drive and future expansion. Or, if you have a video card that requires a PCIe x 16 slot and a SATA controller that requires a PCIe x 1 slot you will need to pick a motherboard with enough expansion slots to meet your needs.
Motherboard Form Factor Types
There are a few different sizes of motherboard. The motherboards form factor is what determines the size and features available on a motherboard. This form factor also determines what case and power supply you will need. It’s important to know what form factor you want before buying your motherboard. The most common and popular form factors are the ATX, microATX, and Mini-ITX. The motherboard shown above has an ATX form factor.
|Form Factor||Motherboard Size||Description|
|ATX||Up to 12″ x 9.6″ (305mm × 244mm)||This is one of the most popular form factors and has had multiple revisions and variations|
|MicroATX||Up to 9.6″ x 9.6″ (244mm × 244mm)||A Smaller version of the ATX|
|Mini-ITX (ITX)||Up to 6.7″ x 6.7″ (170mm x 170mm)||A small form factor that is commonly used in home theater systems & low-end computers. These motherboards are often used in combination with an Intel Atom processor and can be purchased as a motherboard-processor combo unit.|
|FlexATX||Up to 9″ x 7.5″||Smaller version of MicroATX|
|BTX||Up to 12.8″ wide||BTX motherboards can have up to seven expansion slots, are designed for improved airflow, and can use an ATX power supply|
|MicroBTX||Up to 10.4″ wide||A smaller version of BTX and can have up to four expansion slots|
|PicoBTX||Up to 8″ wide||A smaller version of MicroBTX and can have up to two expansion slots|
|NLX||Up to 9″ x 13.6″||Used in low-end systems with a riser card|
Expansion Slots & Data Bus Speeds
The motherboard is covered with tiny lines on both the top and bottom side of the board. These lines are actually small pathways, sometimes called traces, that allow data, power, and instructions to move between components on the motherboard. This collection of pathways over which motherboard devices communicate and the protocol or methods used for transmission, is called a bus. All of this activity on a bus is transmitted in binary, meaning that there are only two states. The two states of binary are on and off. This binary data is placed on a line by applying a small amount of voltage. Motherboard devices such as the CPU interpret this voltage or lack there of on each line as a binary digit of 0 or 1. These 0s and 1s are traveling all over the trace lines and being read and transmitted by related components. The data bus is used to carry data. The data bus comes in different sizes or widths. The width of the data bus is called the data path size. Common data path sizes range from 8, 16, 32, 64, or 128 bits. That means that a bus with 16 lines or traces is called a 16 bit bus, while a bus with 128 lines or traces is called a 128 bit bus. Buses can also carry, control signals needed to coordinate activity, power needed for components, as well as memory addresses used to tell a program where data is stored. The system clock is a pathway on a bus that is dedicated to keeping all of the activities and components on the motherboard in sync. For the system clock to work, the chipset generates a continuously pulsing signal on one end of the system bus. This pulse is then picked up by other components on the motherboard. The frequency of the front side bus, CPU, RAM and other motherboard components is measured in hertz (Hz).
|1 hertz (Hz)||one cycle per second|
|1 megahertz (MHz)||one million cycles per second|
|1 gigahertz (GHz)||one billion cycles per second|
If you look at a stick of RAM, you will see that it is rated in MHz. Common ratings for RAM include 1333 or 1866 MHz. The FSB is commonly rated at 2600, 2000, 1600, 1333, 1066, 800, & 533 MHz.
There are various expansion buses on the motherboard each using a different protocol, frequency & data path size. Different types of buses include: expansion bus, local bus, local I/O bus & local video bus. An expansion bus includes any bus that does not run in sync with the system clock. Expansion buses are generally connected to the southbridge. A local bus is a bus that runs in sync with the system clock. If a local bus is connected to the I/O controller or southbridge, it is called a local I/O bus. PCI, AGP, PCIe & PCIx are types of expansion buses.
|Bus||Bus Type||Data Path Size (bits)||Throughput (Speed)||Description|
|PCI Express (PCIe) v. 2||Local video & local I/O||Up to 32 lanes||Up to 500 MB/sec per lane in each direction||
|PCI Express (PCIe)||Local video & local I/O||Up to 16 lanes||Up to 250 MB/sec per lane in each direction||
|PCI Extended (PCI-X)||Local I/O||64||Up to 8.5 GB/sec||
|PCI||Local I/O||32 or 64||133 – 532 MB/sec||
|AGP||Local video||32||266 MB/sec – 2.1 GB/sec||
PCI Expansion Slot The conventional Peripheral Component Interconnect (PCI) bus uses parallel communication and has a x32 bit data path that supplies 3.3 or 5 volts of power to an adapter card that operates at 33 or 66MHz. This bus has a throughput speed of 133 – 152 MB/sec. PCI was the first bus that allowed an adapter card to run in sync with the CPU. Since PCI is a shared bus topology, mixing 33 and 66Mhz adapters will slow all adapters down to 33Mhz. These adapters are keyed to fit into slots based on these voltages. Notches in the 5V adapter card and slot are oriented toward the front of the motherboard while notches in in the 3.3V adapter card and slot are positioned towards the rear of the motherboard.
PCIx Expansion Slot The PCIx slot uses a 64 bit data path and has had 3 major revisions. The final revision for this technology is PCIx 3.0. These revisions are all backwards compatible with the traditional PCI cards and slots with the exception of 5V PCI cards. PCIx was designed for the server marketplace which is why we usually dont see this slot on a desktop computer motherboard.
PCI Express (PCIe) Expansion Slot PCIe slots come in four different sizes including x1, x4, x8 & x16. PCI Express uses serial communication and is directly connected to the northbridge for faster high end communications. PCIe is not backward compatible with PCI or PCIx because it uses a completely different design. PCIe was designed to replace these older technologies along with the AGP bus. Today, PCIe has replaced AGP but continues to coexist with PCI for backwards compatibility.
miniPCI Expansion slots miniPCI is used as an internal connector for laptop cards.
CNR Expansion slots CNR (communications and networking riser) slots are found on some motherboards and are designed for networking, audio, and telephony technologies. This slot was developed by Intel to replace its AMR (audio/modem riser) technology. This slot was commonly found on Pentium 4 class motherboards but has now been replaced by onboard components.
AGP 1x, 2x, 4x, 8x Expansion Slots AGP was the preferred video expansion slot standard for a long time but has now been replaced by PCIe. The AGP standard had four major releases. These releases included AGP 1.0, AGP 2.0, AGP Pro & AGP 3.0. These variations of AGP had different throughputs, voltages & speeds. There were also several variations of slots available to AGP cards. These slots were keyed differently to make sure you were putting the right card into the right slot. While this is not a current technology, it is still used by a lot of older computer systems.
|Standard||Speed||Max throughput||Voltage||Supported slots|
|AGP 1.0||1x||266 MB/sec||3.3 V||
|AGP 2.0||1x, 2x, 4x||533 MB/sec – 1.06 GB/sec||3.3 V or 1.5 V||
|AGP Pro||1x, 2x, 4x, 8x||N/A||3.3 V or 1.5 V||
|AGP 3.0||4x, 8x||2.12 GB/sec||1.5 V and 0.8 V||
CPU Socket Types
The processor socket on a motherboard is another important feature to know about. The socket and chipset establish what processors will work with the motherboard. The CPU socket is designed to hold either an Intel or AMD processor. On older motherboards, you may have found a long narrow slot designed to hold a legacy processor but on todays boards, all CPU’s fit into a square socket. There are a few different types of arrays used by CPU’s today. Some of the more important arrays include:
The pin grid array (PGA) socket has a uniform grid of small holes designed to receive the pins attached to the underside of the CPU.
The land grid array (LGA) socket has small blunt pins that are designed to connect to lands on the underside of the CPU.
The flip chip land grid array (FCLGA) or the flip chip pin grid array (FCPGA) processor is flipped over so that the top of the CPU is on the bottom side that makes contact with the socket.
The staggered pin grid array (SPGA) socket has its pins staggered all over the socket to be able to fit more pins into the small space available to the socket.
The ball grid array (BGA) connection is not a socket because the processor is actually soldered onto the motherboard and is sold as a package.
Take care when installing the processor into the socket. Try to avoid touching the socket or bottom of the CPU with your fingers. This can leave behind oil from your fingers and can lead to poor CPU contact. A CPU can only be put into a socket one way, look over the CPU to find a small triangular shaped mark and match this up to a similar mark on the socket. This will ensure your CPU’s orientation to the motherboard is correct before trying to insert the CPU into the socket. To ensure that even force is applied while installing the CPU, there are one or two levers on the side of the socket to be pressed down after dropping the CPU into place. These types of sockets are called zero insertion force (ZIF) sockets and are found on all modern motherboards where the CPU is not soldered on (BGA).
The chipset is a combination of chips on the motherboard that work together with the processor to control RAM, buses & peripheral devises. The manufacturer will usually give the chipset a name and model number. Communications between the CPU and RAM happen over the frontside bus (FSB), which is a set of pathways that connect the CPU to important motherboard components such as RAM & the expansion slots. These components are local to the FSB. The backside bus (BSB) is a set of pathways that exist between the CPU and level 2 or 3 cache memory. Sometimes thee is no BSB, in this case the level 2 or 3 cache memory is placed on the FSB. The northbridge & southbridge are both subsets of the chipset.
The Northbridge manages important, high speed connections between the CPU and RAM as well as connect high-end graphics slots like AGP or PCI Express. The northbridge is connected to and controls the Southbridge; helping to manage communications between the Southbridge and other computer components. The Southbridge manages slower onboard peripheral connections such as USB, Ethernet, PATA, SATA, PS/2, parallel, serial and other integrated components. Basically, this part of the chipset manages anything that does not have an effect on the overall performance of the computer system.
On old legacy motherboards it was common to find that you had to use jumpers to configure the boards settings. A jumper is made up of two small metal pins that stick up off of the motherboard. These jumpers were either open or closed depending on whether or not the pins had a cover. An open jumper has no cover while a closed jumper has a cover over the pins. This corresponding image shows a motherboard jumper with a red cover. These open or closed positions were used for many different settings. These settings included; telling the computer system to turn on or off, a power saving feature, or to configure the speed of the CPU. When not in use, jumper covers can be stored in a “parked” position. This means that the jumper is only connected to one pin and “parked” for later use. This technique helps computer techs keep track of the cover when its not being used.
Jumpers are still found on todays motherboards. Jumpers come in really handy when you need to reset a forgotten BIOS or boot up password. Another use for jumpers today is to reset bios settings incase of a failed flash or improper configuration. Read you motherboard user guide for more information on using jumpers on your motherboard.
Power connections and types
The 24-pin (or 20-pin on older motherboards) power connector is the main power connection for the motherboard.
The 8-pin and 4 pin CPU power connection provides additional power needed by the CPU.
The fan power connection has 4 header pins sticking up off the motherboard and has a small tab that only allows the fan connector to fit one way.
Integrated Connectors & Ports
Other than expansion slots, motherboards also have on board ports and internal connectors. Commonly found integrated components on todays motherboards include USB, PS/2, Ethernet, Audio, Serial, HDMI, VGA & DVI. Depending on your motherboard, you may also find S/PDIF, parallel, FireWire, Thunderbolt, Mini Display & eSATA. The motherboard comes packaged with an I/O shield, sometimes called the backplate, that is installed in the computer case and designed with all the necessary holes for these I/O ports. Some motherboards also come with integrated connector modules that allow the connection of additional ports. These ports are made accessible from the rear of the case and are mounted in same case opening slots that are used by the expansion cards. The internal connectors or headers available vary depending on what mobo you have. Commonly found connectors and headers include PATA, IDE, Floppy, USB, SATA, Audio, S/PDIF & FireWire. For a more in depth look at all of the different ports found on a computer, check out the computer inside & out article.