Motherboards are complex. Let’s break them down, component by component, and explain how they work.1 2
Choosing a motherboard is a hugely important part of building a PC.
What does a motherboard do? It’s the circuit board that connects all of your hardware to your processor, distributes electricity from your power supply, and defines the types of storage devices, memory modules, and graphics cards (among other expansion cards) that can connect to your PC.
Below, we’ll dive into motherboard anatomy and give you all the information you need to learn how to choose a motherboard for your build.
A motherboard is a PC’s primary circuit board. Though motherboard aesthetics change over time, their basic design makes it easy to connect new expansion cards, hard drives, and memory modules, as well as replace old ones.
Let’s walk through some of the terms you’ll encounter when comparing motherboards.
Motherboards usually contain at least one processor socket, enabling your CPU (the PC’s mechanical “brain”) to communicate with other critical components. These include memory (RAM), storage, and other devices installed in expansion slots — both internal devices like GPUs and external devices like peripherals.
(Not all motherboards have a socket, though: in systems with less space, like Intel® NUC and most laptops, the CPU is soldered into the motherboard.)
When selecting a motherboard, check your CPU’s documentation to ensure the board is compatible with your CPU. Sockets vary in order to support different products based on generation, performance, and other factors by changing the pin array. (The name of the socket comes from the pin array: for example, the LGA 1151 socket, compatible with 9th Gen CPUs, has 1,151 pins.)
Modern Intel motherboards connect CPUs directly to RAM, from which it fetches instructions from different programs, as well as to some expansion slots that can hold performance-critical components such as GPUs and storage drives. The memory controller lives on the CPU itself, but numerous other devices communicate with the CPU through the chipset, which controls many expansion slots, SATA connections, USB ports, and sound and network functions.
Some pins connect the CPU to memory via traces (lines of conductive metal) on your motherboard, while others are groups of power or ground pins. If your PC is having trouble booting up or recognizing installed memory, it could be caused by a bent pin that isn’t making contact with your CPU, among other potential issues.
Pins may be located on the motherboard or the processor package itself, depending on the socket type. Older sockets (such as Intel’s Socket 1) were often Pin Grid Arrays (PGA), in which pins located on the CPU fit into conductive lands on the socket.
Land Grid Array (LGA) sockets, used in many modern chipsets, essentially work the opposite way: pins on the socket connect to conductive lands on the CPU. LGA 1151 is one example of this socket type.
Today’s processor sockets use ZIF (Zero Insertion Force) installation. This means you only have to fit the processor into place and secure it with a latch, without applying extra pressure that could bend pins out of place.
This innovation came into use with Intel’s Socket 1 in 1989, which worked with the 80486 (or 486) CPU. Though early designs for Socket 1 could require up to 100 pounds of force to insert a CPU, within the same CPU generation manufacturers were able to develop user-friendly designs that required virtually no force and no tools to install.
The chipset is a silicon backbone integrated into the motherboard that works with specific CPU generations. It relays communications between the CPU and the many connected storage and expansion devices.
While the CPU connects directly to RAM (via its built-in memory controller) and to a limited number of PCIe* lanes (expansion slots), the chipset acts as a hub that controls the other buses on the motherboard: additional PCIe lanes, storage devices, external ports like USB slots, and many peripherals.
Higher-end chipsets can feature more PCIe slots and USB ports than standard models, as well as newer hardware configurations and different allocations of PCIe slots (with more linked directly to the CPU).
The classic chipset design, common to chipsets for the Intel® Pentium® processor family, was divided into a “northbridge” and “southbridge” that handled different functions of the motherboard. Together, the two chips formed the chip “set.”
In this older design, the northbridge, or “memory controller hub,” was linked directly to the CPU via a high-speed interface called the system bus or front-side bus (FSB). This controlled the system’s performance-critical components: memory and the expansion bus that connected to a graphics card. The southbridge, or “I/O Controller Hub,” was connected to the northbridge with a slower internal bus, and controlled virtually everything else: other expansion slots, Ethernet and USB ports, onboard audio, and more.
Starting with 1st Gen Intel® Core™ processor in 2008, Intel chipsets have integrated the functions of the Northbridge into the CPU. The memory controller, one of the major factors affecting chipset performance, is now within the CPU itself, reducing lag in communications between the CPU and RAM. The CPU connects to a single chip (rather than two) — the Platform Controller Hub (PCH), which controls PCIe lanes, I/O functions, Ethernet, the CPU clock, and more. A high-speed Direct Media Interface (DMI) bus creates a point-to-point connection between the CPU’s memory controller and the PCH.
Choosing a Chipset
Modern chipsets consolidate many features that were once discrete components connected to motherboards. Onboard audio, Wi-Fi, Bluetooth®3 technology, and even cryptographic firmware are now integrated into Intel chipsets.
High-end chipsets like Z390 can offer many benefits, including overclocking support, and higher bus speeds. But Intel chipsets also provide further improvements.
Here’s a quick breakdown of the differences between Intel’s chipset series:
- Overclocking support for CPUs with “K” designation
- Maximum of 24 PCIe lanes
- Up to six USB 3.1 Gen 2 ports
- No overclocking support
- Maximum of 20 PCIe lanes
- Up to four USB 3.1 Gen 2 ports
- No overclocking support
- Maximum of 20 PCIe lanes
- USB 3.0 ports only
These different options enable entry at a variety of price points, while still taking advantage of the benefits of the 300-series chipset.
Peripheral Component Interconnect Express (PCIe) is a high-speed serial expansion bus integrated into either your CPU, motherboard’s chipset, or both. This allows the installation of devices like graphics cards, solid-state drives, network adapters, RAID controller cards, capture cards, and many other expansion cards into the PCIe slots of a motherboard. The integrated peripherals featured on many motherboards also connect via PCIe.
Each PCIe link contains a specified number of data lanes, listed as ×1, ×4, ×8, or ×16 (often pronounced “by one,” “by four,” etc.). Each lane consists of two pairs of wires: one transmits data and the other receives data.
With current-generation PCIe implementations, a PCIe ×1 link has one data lane with a transfer rate of one bit per cycle. A PCIe×16 lane, typically the longest slot on your motherboard (and also the one used most often for a graphics card), has 16 data lanes capable of transferring up to 16 bits per cycle. However, future iterations of PCIe will allow doubling the data rate per clock cycle.
Each revision of PCIe has roughly doubled the bandwidth of the previous generation, and that means better performance for PCIe devices. A PCIe 2.0 ×16 link has a theoretical, bidirectional peak bandwidth of 16 GB/s; a PCIe 3.0 ×16 link has a peak of 32 GB/s. When comparing PCIe 3.0 lanes, the ×4 link commonly used by many solid-state drives has a peak theoretical bandwidth of 8 GB/s, whereas the ×16 link that GPUs leverage offers four times as much.
Another feature of PCIe is the option to use slots with more lanes as a substitute for slots with fewer lanes. For example, a ×4 expansion card can be inserted into a ×16 slot and work normally. However, its throughput will be the same as if it was in a ×4 slot — the 12 additional lanes simply go unused.
Some motherboards have M.2 and PCIe slots that could use more PCIe lanes than are actually available on the platform. For example, some motherboards may have seven PCIe x16 slots, which could theoretically use 112 lanes, but the processor and chipset may feature only 48 lanes.
If all lanes are in use, PCIe slots will often switch to a lower bandwidth configuration. For example, if a pair of GPUs are installed in two ×16 PCIe slots, the links may run at ×8 rather than ×16 (modern GPUs are unlikely to be bottlenecked by a PCIe 3.0 ×8 connection). Some premium motherboards may use PCIe switches that fan out the physical lanes, however, so the slot lane configurations can remain unchanged.
Enthusiast motherboards, such as the Z-series, provide more PCIe lanes and greater flexibility for PC builders.
M.2 and U.2
M.2 is a compact form factor that fits small expansion devices (16-110mm long), including NVMe (non-volatile memory express) solid-state drives, Intel® Optane™ memory, Wi-Fi cards, and other devices.
M.2 devices have different “keys” (the arrangement of gold connections on the end) that determine compatibility with the socket on the motherboard. Though they can use many different interfaces, the most common M.2 cards use four PCIe low-latency data lanes or the older SATA bus.
Because M.2 cards are relatively small, they provide an easy way to expand storage capacity or system capability in a smaller system. They plug directly into the motherboard, thereby eliminating the cables necessary with traditional SATA-based devices.
U.2 connectors are an alternative interface that connects to 2.5” SSDs that use cabled PCIe connections. U.2 storage drives are frequently used in professional settings such as data centers and servers, though less frequently in consumer builds.
U.2 and M.2 both use the same number of PCIe lanes and are capable of comparable speeds, though U.2 supports hot swapping (meaning the drive can be removed while the system using it remains on) and can support more power configurations than M.2.
SATA (Serial ATA) is an older computer bus less commonly used today to connect to 2.5" or 3.5" hard drives, solid-state drives, and optical drives that play DVDs and Blu-ray.
Though slower than PCIe, the common SATA 3.0 interface supports data transfer speeds up to 6Gbit/s. The newer SATA Express (or SATAe) format uses two PCIe lanes to reach speeds up to 16Gbit/s. It’s not to be confused with External SATA (eSATA), an external port that allows easy connection of (compatible) portable hard drives.
Expansion slots have been an expected feature of PC motherboards since the launch of the original IBM Personal Computer in 1981, which used a 16-bit expansion bus called ISA (Industry Standard Architecture). This was followed by several other expansion bus standards, such as PCI (Peripheral Component Interconnect) VESA Local Bus, PCI-X, and AGP (Accelerated Graphics Port), a point-to-point refinement of the PCI standard used to connect graphics cards to the northbridge.
The key difference between PCIe and the preceding PCI technology is its use of serial, rather than parallel, links. The parallel data transfers of PCI meant that the shared bus was limited to the speed of the slowest peripheral connected to it. PCIe provides point-to-point connections for each individual device, with each lane transferring bits sequentially.
Motherboards also have slots for RAM modules: sticks of volatile memory that temporarily store data for fast retrieval. Multiple sticks of high-speed RAM can help PCs handle simultaneous programs without slowdown.
Full-size motherboards (like the ATX form factor) typically have four slots, while size-constrained boards like mITX usually use two. However, HEDT motherboards, like those for the Intel® Core™ X-series processor family (as well as server/workstation motherboards based on the Intel® Xeon® platform) can have up to eight.
Recent Intel motherboards support dual-channel memory architecture, meaning there are two independent channels transferring data between the CPU’s memory controller and a stick of DIMM (dual in-line memory modules) RAM. As long as sticks of RAM are installed in pairs with matching frequencies, this leads to speedier data transfer and better performance in some applications.
In older chipsets, the CPU usually communicated with RAM in a multi-step process through its link to the northbridge/memory controller via the front-side bus. In modern Intel chipsets, the memory controller is integrated into the CPU, and is accessed through a low-latency, point-to-point link called the Intel® Ultra Path Interconnect (Intel® UPI).
Your motherboard’s form factor determines the size of case you need, the number of expansion slots you’ll have to work with, and many facets of the motherboard’s layout and cooling. In general, larger form factors give builders more DIMM, full-size PCIe, and M.2 slots to work with.
To make things easier for both consumers and manufacturers, desktop motherboard dimensions are highly standardized. Laptop motherboard form factors, on the other hand, often vary by manufacturer due to the unique size constraints. This can also be true for highly specialized pre-built desktops.
Common desktop motherboard form factors are:
- ATX (12” × 9.6”): The current standard for full-size motherboards. A standard consumer ATX motherboard usually features seven expansion slots, spaced 0.7” apart, and four DIMM (memory) slots.
- Extended ATX or eATX (12” x 13”): A larger variant of the ATX form factor designed for enthusiast and professional use, these boards have additional real estate for more flexible hardware configurations.
- Micro ATX (9.6” × 9.6”): A more compact variant of ATX featuring two full-size (×16) expansion slots and four DIMM slots. Fits into mini-towers, but remains compatible with the mounting holes in larger ATX cases.
- Mini-ITX (6.7” × 6.7”): Small form factor designed for use in compact computers without fan cooling. Provides one full-size PCIe slot and typically two DIMM slots. Mounting holes are again compatible with ATX cases.
What You Need to Know About BIOS
The first thing you see when your computer starts up is the BIOS, or Basic Input/Output System. This is the firmware that loads before your operating system boots up, and it’s responsible for starting up and testing all connected hardware.
Though often referred to as the BIOS by users and motherboard labels alike, the firmware on modern motherboards is typically UEFI (Unified Extensible Firmware Interface). This more flexible environment boasts many user-friendly improvements, such as support for larger storage partitions, speedier boot-up, and a modern GUI (graphical user interface).
Motherboard manufacturers often add UEFI utilities that streamline the process of overclocking the PC’s CPU or memory and provide helpful presets. They may also feature a stylized appearance, add logging and screenshot features, simplify processes like booting from another drive, and display monitor memory, temperature, and fan speeds.
UEFI also supports older features of the BIOS. Users can boot into Legacy mode (also known as CSM, or Compatibility Support Module) to access the classic BIOS, which may solve compatibility issues with older operating programs or utilities. However, when users boot in Legacy mode, they obviously lose the modern benefits of UEFI, such as support for partitions over 2TB. (Note: always backup important data before switching boot modes).
To power up every part of your motherboard, cables from the power supply and case must be plugged into connectors and headers (exposed pins) on the motherboard. Consult the visual reference in your manual, as well as the small text silkscreened onto your motherboard itself (such as CPU_FAN), to match each cable to the right connector.
Power and Data Connectors
- 24-pin power connector
- 8- or 4-pin 12V CPU power connector
- PCIe power connector
- SATA Express/SATA 3 connectors
- M.2 connectors
- Front-panel header: a group of individual pins for the power button, reset button, hard drive LED, power LED, internal speaker, and case features
- Front panel audio header: powers headphone and speaker ports
- Fan and pump headers: for CPU, system, and water cooling
- USB 2.0, 3.0, and 3.1 headers
- S/PDIF (digital audio) header
- RGB strip headers
Your motherboard is the hub that external devices connect to, and its I/O controller manages these devices. Consumer motherboards provide ports that connect a CPU’s integrated graphics to your monitor (useful if you don’t have a discrete graphics card or are troubleshooting display issues), peripherals like a keyboard and mouse, audio devices, Ethernet cables, and more. Different revisions of these ports, like USB 3.1 Gen 2, can allow greater speeds.
Motherboards group external ports on their back panel, which is covered with a removable or integrated “I/O shield” that is grounded due to its contact with an often metal case. This is sometimes attached to the motherboard, or comes separately to be installed when putting together the system.
Peripherals and Data Transfer
- USB port: A ubiquitous port used to connect to mice, keyboards, headphones, smartphones, cameras, and other peripherals. It provides both power and data (at speeds up to 20 GBit/s using USB 3.2). Current motherboards may feature both the classic USB Type-A connector and the slimmer, reversible Type-C connector.
- Thunderbolt™ 3 port: A high-speed port that uses a USB-C connector. Thunderbolt™ 3 technology transfers data at speeds up to 40 GB/s and also supports the DisplayPort 1.2 and USB 3.1 standards. DisplayPort support makes it possible to “daisy chain” multiple compatible monitors and drive them from the same PC.
- PS/2 port: A legacy port, this color-coded six-pin connection connects to a keyboard or mouse.
These display ports connect to your motherboard’s onboard graphics solution; a graphics card installed in one of your expansion slots will provide its own display port options.
- HDMI (High-Definition Multimedia Interface): This ubiquitous digital connection supports resolutions up to 8K at 30Hz as of the HDMI 2.1 revision.
- DisplayPort: This display standard supports resolutions up to 8K at 60Hz as of DisplayPort 1.4. Though more common on graphics cards than motherboards, many boards feature DisplayPort support through their Thunderbolt™ 3 port.
- DVI (Digital Video Interface): A legacy port dating back to 1999, this digital 29-pin connection can be either single-link or higher-bandwidth dual-link DVI. Dual-link supports resolutions up to 2560 × 1600 at 60Hz. It easily connects to VGA with an adapter.
- VGA (Video Graphics Array): An analog 15-pin connection with support for resolutions up to 2048 × 1536 at an 85Hz refresh rate. This legacy port is still sometimes seen on motherboards. Often suffers signal degradation with higher resolutions or shorter cables.
The front of a PC case often features two analog 3.5mm audio ports labeled for headphones (headphone out) and a microphone (mic in).
The motherboard’s rear panel usually has a bank of six color-coded and labeled 3.5mm analog audio ports for connecting to multichannel speaker systems.
The colors of the audio ports on your motherboard may vary by manufacturer, but these are standard:
Black is the rear speaker out
Orange is the center speaker/subwoofer out
Pink is the mic in
Green is the front speaker (or headphones) out
Blue is the line-in
Silver is the side speaker out
Your motherboard may also feature S/PDIF (Sony/Philips Digital Interface) connectors, such as a coaxial and optical audio port, that work with digital speakers, home theater receivers, and other audio devices. This can be a useful option if the device you’re using doesn’t support audio transfer via HDMI.
Most consumer motherboards include an RJ45 LAN port, which can connect to your router or modem via Ethernet cable. Some boards feature dual ports for use with a Wi-Fi antenna, as well as advanced connectivity features, such as dual 10-Gigabit Ethernet ports.
What’s a PCB?
It’s helpful to know a few basic terms related to motherboard manufacturing, as manufacturer ads and manuals often reference their methods of PCB construction.
A modern motherboard is a printed circuit board (PCB) made of layers of fiberglass and copper, with other components mounted on it or socketed into it.
Modern PCBs usually have around 10 layers, making them much more densely interconnected than they appear on the surface.
Each conductive “trace” — the visible lines covering the surface of the board — is a separate electrical connection. If one of these traces gets damaged, the circuit is no longer complete, and motherboard components will cease to function properly. For example, if a trace leading from a PCIe link to the PCH is deeply scratched, the PCIe slot may no longer power the expansion card installed in it.
After conductive traces are created via chemical etching, manufacturers add the solder mask, a traditionally green polymer coating that helps prevent oxidation. It also helps prevent handling damage, ensuring that traces won’t be disrupted by a minor scratch or bump as you install the motherboard in its case.
What Else Do Manufacturers Add?
Though motherboard manufacturers don’t create their own chipsets, they make countless decisions involving manufacturing, aesthetics, and layout, as well as cooling, BIOS features, Windows motherboard software, and premium features. While the range of these features is too wide to fully cover, common additions fall into a few general categories.
High-end motherboards often provide automated testing and tuning to overclock your CPU, GPU, and memory, providing an easy-to-use alternative to manual adjustment of frequency and voltage numbers in the UEFI environment. They may also feature an onboard clock generator for fine control of CPU speed, an enhanced VRM (Voltage Regulator Module), extra thermal sensors near overclocked components, and even physical buttons on the motherboard to start and stop overclocking. You can learn more about overclocking your PC here.
Motherboard components such as the PCH and VRM generate significant heat. To keep them at safe operating temperatures and prevent performance throttling, motherboard manufacturers install a variety of cooling solutions. These range from the passive cooling provided by heatsinks to active solutions, such as small fans or integrated water cooling.
Active cooling solutions have moving parts, like the pump in a water cooler or a spinning fan. Passive cooling solutions, like heat sinks, work without moving parts. The latter are sometimes preferred in rugged conditions, where active solutions may have a shorter lifespan, or when lower acoustics are preferred.
Motherboard software suites make it easier to manage your motherboard within Windows. Feature sets vary between manufacturers, but the software may scan for outdated drivers, automatically monitor temperatures, safely update the motherboard BIOS, allow easy adjustment of fan speeds, offer more in-depth power-saving profiles than Windows* 10, or even track network traffic.
Advanced audio codecs, built-in amplifiers, and enhanced capacitors can improve the output of onboard audio systems. Different audio channels may also be separated in different layers of the PCB to avoid signal interference.
Many manufacturers advertise PCB construction techniques said to help isolate memory circuits and improve signal integrity. Some motherboards also add extra steel plating on top of the PCB to protect connectors or support the graphics card (usually secured with a simple latch).
High-end motherboards often provide RGB headers to power an array of LED lights with customizable colors and effects. Non-addressable RGB headers power LED strips that display a single color at a time (with varying intensities and effects). Addressable RGB headers power LEDs with multiple color channels, allowing them to display several hues at once. Built-in software and smartphone apps typically make configuration of LEDs easy.
Make Your Choice
Whether you're planning your next build or upgrading your current PC, understanding the components of your motherboard is crucial. Once you know what everything does, you’ll know how to choose a motherboard that suits your build.
You need a socket that matches your CPU, a chipset that maximizes the potential of your hardware, and finally a feature set that matches your computing needs. Take the time to list out several compatible motherboards and compare their key advantages before making a decision, and you should find exactly what you are looking for.