Motherboards 101
Folks who shop for motherboards—whether as an upgrade component or for a build-a-PC-from-scratch project—are a savvy bunch, confident enough to take their PC to pieces and put it back together again. The terminology around motherboards can be bewildering, though, and some of it can stump even experienced PC builders.
First-time buyers and builders, meanwhile, definitely need to go into a motherboard purchase with a bit of background knowledge (or a savvy friend!) to get a board that fits—both literally in the PC's chassis, and in a usage sense. So, if you don't have that friend, let us be it: Here's a 101-level primer to the lingo you need to talk motherboard.
Form Factor (ATX, MicroATX, Mini-ITX)
"Form factor" is shorthand for the dimensions and layout of a given desktop motherboard. To be sure that a given board will fit into a PC case, you need to know which of the standard board form factors the case supports.
Left to right: ATX, MicroATX, and Mini-ITX boards
The ones that matter most to PC builders and upgraders are ATX, MicroATX, and Mini-ITX. ATX is sometimes referred to as "standard ATX," and ATX boards (usually, but not exclusively) measure 9.6x12 inches. They're what you'll see in most midtower or larger PC cases—what most of us think of as traditional tower PCs. A few multi-CPU boards, intended for servers and workstations, and some outliers (such as EVGA's Classified series boards) support larger ATX "standards" such as Extended ATX and XL-ATX, but these won't be of interest to most PC upgraders or builders. The key thing to know apart from the size factor: ATX boards will have more expansion slots than MicroATX or Mini-ITX ones.
Smaller towers ("minitowers"), flat-style "desktop" cases, and home theater PC (HTPC) chassis tend to support boards of the MicroATX or Mini-ITX kind. MicroATX boards measure up to 9.6 inches square (some are smaller) and have fewer slots than an equivalent ATX board, usually enough to install a video card and a supplementary card or two. The 6.7-inch-square Mini-ITX standard, meanwhile, defines boards even more compact, intended for tight builds in small-form-factor (SFF) PCs. With Mini-ITX, you're usually limited to just one expansion slot.
Note that most PC cases that support a particular form factor also support boards of the form factors smaller than it—but always check the specs for confirmation of that before buying a new board or case.
BIOS and UEFI BIOS
The basic input/output system (BIOS) is the long-standard firmware that manages your PC outside the operating-system environment—that is, before you boot up. Accessed during the startup sequence, the BIOS lives in a dedicated chip on the motherboard (on some motherboards, the chip is actually removable/swappable) and governs crucial system settings such as the boot-device order, as well as parameters for integrated components. Overclockers can also tweak system fundamentals in here, though it's possible with the right board and software to overclock from within Windows, too.
Sample UEFI BIOS from a Gigabyte motherboard
UEFI (Unified Extensible Firmware Interface) is a 21st-century refinement of the old-school BIOS, which was long past its expiration date due to a variety of inherent limitations. The product of an Intel initiative to update the legacy BIOS environment, UEFI is now managed by a consortium of hardware and software vendors.
The UEFI BIOS outlines something closer to a mini operating system, with more modular programmability and much greater customization possibilities for board makers. Depending on the design, a UEFI BIOS may also be mouse-navigable. For motherboard buyers, the presence of a UEFI BIOS was, for a time, a definite plus to look out for. Now, it's the standard.
I/O Shield
If you've ever assembled a PC from parts, you've probably cut your finger on one of these. The I/O shield is a rectangular metal plate (the edges can be sharp) that snaps into a gap on the back of your PC case. Just about every motherboard includes one. The shield will have cutouts for the specific ports on the motherboard, and it protects the rest of the board during everyday use when you insert cables into the ports.
Most I/O shields are not interchangeable between different models of motherboard. (The only things standard about them are their overall dimensions, roughly 1.75x6.5 inches, which ensure that they'll fit in a typical PC case.) So you'll want to be sure, if you're buying a secondhand motherboard, that the seller includes the I/O shield in the box. They tend to get misplaced during upgrades, and it can be tricky getting a replacement that fits, since they are board-specific.
Chipset
"Chipset" is a broad term encompassing the silicon on a motherboard that provides the pathways between (and the controllers for) the various subsystems within a computer. In a motherboard shopper's context, the chipset, usually from Intel or AMD, defines the board family, the specific AMD or Intel processor lines that the board supports, and many of the possible features that the motherboard maker could implement. A motherboard maker will typically offer a whole host of boards based on a single chipset, but with differences in form factors and feature levels.
The usual course of things in the motherboard world is that when a new processor line debuts, a new high-end chipset will accompany it, and lesser-featured, cheaper chipsets for the same processor family will debut at the same time or a bit later. These "step-down" chipsets allow for more budget-minded motherboards for different usage cases. When we wrote this in mid-2018, for example, the newest Intel chipsets for its mainstream CPUs in the 8th Generation Core "Coffee Lake" line were the enthusiast-minded Z370 (stacked with overclocking features) and a host of lower-featured chipsets geared toward more ordinary boards: the Q370, H370, B360, and H310. The previous generation of Intel boards followed the same rough numeric paradigm: the top-end Z270 chipset, accompanied by Q270, H270, Q250, and B250 for mainstream Socket 1151 "Kaby Lake" processors.
The X299, meanwhile, is the latest chipset for Intel's high-end Socket 2066 "Core X-Series" processors, supplanting the X99 (for Socket 2011) as the "extreme enthusiast" chipset on the Intel side of the aisle. AMD's enthusiast equivalent to the Core X-Series, the Ryzen Threadripper, relies on a single chipset, the X399.
AMD boards in the past employed a variety of AMD chipsets too extensive to list here, but AMD's Ryzen processors have coalesced around the AM4 socket and the X370 and B350 chipsets, with a few other lower-end Ryzen-compatible chipsets (such as the A320) appearing on budget boards. In 2018, the X370 has been joined by the X470, which adds support for second-gen Ryzen CPUs and the new-for-2018 Ryzen "Raven Ridge" chips with on-chip graphics.
Knowing which chipset your board runs on is important for two reasons. For one, it is related to which specific CPUs the motherboard supports (though you should check that list carefully, regardless). Second, the chipset indicates the relative positioning of a board and its feature set. For example, AMD B350-based boards tend to be more budget-minded models than the X370s, though both may support the same CPUs.
CPU Socket
This is the square receptacle into which the processor chip that you purchase fits. The processor's specific socket type (not just the manufacturer) needs to match the socket type used by the board. (In other words, not all Intel processor chips work in all Intel boards...not by a long shot.) Also, not all processors of a given socket type will work in every board that has that socket. You'll want to check the motherboard maker's CPU-compatibility list for details.
For some time now, Intel's processors have used a design in which the interface pins are part of the socket, with dot-like contacts on the bottom of the processor chip. AMD's consumer chips, meanwhile, with the exception of the Ryzen Threadrippers, still use old-school sockets with holes for pins on the chip.
The most common socket types you'll run across here in 2018, as we write this, are...
• Socket 2011 and Socket 2066. Not referring to the year of introduction but the number of pins in the socket, these are the sockets used by Intel's highest-end processors, such as the Intel Core i7-6950X Extreme Edition (Socket 2011) and newer Core i9-7980XE Extreme Edition (Socket 2066). Socket 2066 is new with Intel's 2017 Core X-Series of CPUs, and Intel refers to this class of system generically as HEDT (for "high-end desktop"). Note also that Socket 2011 comes in two variants, the original and a later Socket 2011 v3, that are electrically incompatible.
Intel's Socket 2011; Socket 2066 looks similar
• Socket 1151. The current mainstream socket used by Intel's latest Core, Celeron, and Pentium processors, the 1151 socket came in with Intel's 6th Generation Core ("Skylake") chips and also covers the 7th Generation Core ("Kaby Lake") and 8th Generation ("Coffee Lake") Intel chips. It succeeds Socket 1150. Important to know: Just because a CPU is compatible with Socket 1151, it doesn't mean that every Socket 1151 motherboard supports that CPU. Check the board specs! The "Coffee Lake" generation of CPUs, for example, works only with Socket 1151 boards based on 300-series chipsets, and these boards do not support earlier (6th and 7th Generation) Socket 1151 CPUs.
Intel Socket 1151, mainstream staple socket, with protective cover
• AMD AM4. Used by AMD's latest APU chips and by its Ryzen mainstream/enthusiast processor line, AM4 is a new, unifying socket for AMD's consumer CPUs. Again, though, you'll want to look for a specific CPU support list for an AM4 board; newer AM4 CPUs, such as the AMD Ryzen 7 2700X, may not work in older AM4 boards out of the box.
AMD's AM4 socket, showing pin receptacles
• AMD TR4. This enormous socket is used by AMD's Ryzen Threadripper CPUs and employs a whopping 4,096 pins and a special loading mechanism. It's similar to that used by AMD's Epyc server CPUs.
AMD Threadripper TR4 socket, with CPU being installed
• AMD FM2 and FM2+. These sockets were used by AMD's so-called "accelerated processing units" (APUs), which is AMD's marketing term (now in common use) for its CPUs that have on-chip video acceleration. The FM2+ socket emerged in late 2013 for use with the 2014 "Kaveri" family of APUs, but older FM2-compatible APUs will work in FM2+ boards as well. It's now a dead end, though.
• AMD AM3+. This socket was used by the last wave of AMD's FX-series processors, which are CPUs only, with no integrated graphics. It is also a dead end.
DIMM Slots
For "dual in-line memory module." These are the slots on the motherboard (typically two or four, but sometimes eight) that accept the system's RAM. Levers on one or both sides lock the memory sticks into place.
In the latest consumer motherboards, this will be dual data rate 4 (DDR4) memory. (DDR3 slots are still around in some last-generation motherboards, notably for AMD's pre-Ryzen CPUs.) Where the "DDR" comes in: You'll generally see a performance benefit if RAM sticks are used in identical pairs and inserted in designated "paired" slots on the motherboard for dual-channel throughput. Quad-channel memory (using four or eight sticks per set) is supported by a few high-end platforms, such as Intel's X299 for the Core X-Series CPUs. It works under the same general principles as dual-channel.
DIMM slots on a late-model MSI motherboard
RAM is often sold packaged to facilitate dual- or quad-channel operation (as a set of two or four modules with the same specs), and the motherboard's paired slots are sometimes color-coded. With paired memory, you'd put the two (dual-channel) or four (quad-channel) modules in slots with matching colors, or arranged according to the motherboard manual's instructions.
The takeaway: When shopping for RAM, know that two sticks of DDR memory adding up to a certain capacity can deliver better performance than just one stick of that capacity, all else being equal, thanks to dual-channel throughput. (Ditto four sticks versus two or just one, if the board supports quad-channel.)
PCI Express x16, x8, x4, and x1 Slots
Abbreviated "PCIe slots," these are the expansion slots on the motherboard that accept video cards, TV tuners, and other board-based components. The "x" designation describes two things, however: the physical size of the slot, and the bandwidth of the slot itself. And these two numbers can be different for a single given slot.
In terms of the slot size, the higher the "x" number, the longer the slot, and you'll ideally want to match a card with the same kind of slot. In practice, you'll see these days only x16 (long) and x1 (short) physical slots on new motherboards. A card with a lower "x" designation can be used in a higher-numbered slot, but not vice versa. (So, for example, you can install a PCIe x1 card in a PCIe x16 slot, but not the other way around.)
Board close-up showing x16 and x1 physical slots (x16 slots are long and banded in silver)
Where things get complicated is with PCI slot bandwidth, though it's mostly relevant only when installing dedicated graphics cards. Modern video cards all slot into PCI Express x16 slots, and a motherboard may have several of these. It's possible, however, that not all of the x16 slots on a board (and perhaps, just one of them) supports full PCI Express x16 bandwidth or lanes, despite being capable of fitting an x16-length card. (Simply put, the lanes are electrical pathways that enable throughput; more is better.) If you're installing just one video card, it's important to put it in an x16 slot that supports full x16 bandwidth, as opposed one with x8 or x4 lanes only.
Boards that support Nvidia SLI and/or AMD CrossFireX multiple-video-card setups (see below) will also have different possible lane/bandwidth configurations that you should be aware of, if you intend to install multiple video cards. Using one card in one slot might give you x16 bandwidth with that card, but adding a second card might bump both cards down to x8, or one might run at x16 with the other at x8 or x4. Examine the bandwidth specs before buying if multicard gaming is your aim to make sure you'll get the most performance possible from your card investment.
SLI and CrossFireX
Two flavors of the same dish, these terms refer to the ability of a motherboard to accept more than one graphics card and have the cards work additively to increase graphics performance. Scalable Link Interface (SLI) is the standard that works with Nvidia GeForce graphics cards, while CrossFireX works with AMD's Radeon cards. The cards need to employ the same graphics processor. A physical bridging connector between cards, often supplied with SLI- or CrossFire-compatible motherboards, may be required for adequate bandwidth for communication between the cards. The latest of Nvidia's high-end GeForce GTX 1000-series cards require a special "high-bandwidth" SLI connector to maximize SLI performance.
With SLI, a board may support Two-Way, Three-Way, or Four-Way SLI, which indicates the maximum number of cards supported, but with the Nvidia "Pascal" video cards in its GTX 1000 series, Nvidia's new limit is just two cards officially supported in SLI, and some Pascal cards in the line don't work in SLI at all. CrossFireX can be two to four cards; check the board specs for how many are supported.
Two GeForce GTX 1080 cards in SLI, connected by a high-bandwidth bridge
On some AMD-based boards from the generations before the Ryzen CPUs, don't confuse SLI or CrossFireX with "AMD Dual Graphics," which is a different feature altogether. With Dual Graphics, you can pair certain AMD Radeon cards with the CPU's onboard graphics in a CrossFire-like performance-boosting arrangement. It's a modest boost at best, though.
Also, know that a given game needs to have specific support for SLI or CrossFireX to see much of a benefit, and that this support is being de-emphasized by many game developers these days. For most users, a single powerful video card will more than suffice. (See our guide to the best graphics cards.)
USB 2.0, USB 3.0, and USB 3.1 Gen2 Headers
Another kind of on-motherboard pin header, USB headers nowadays come in three types: USB 2.0, USB 3.0, and USB 3.1. These connect to matching wires in your PC's chassis that lead to "front panel" USB connectors situated on the case's exterior.
A USB 2.0 header will have two rows of five pins, with one pin missing out of the 10 as a "key" for proper orientation of the connector. The matching cable connector on your PC's case will have 10 pinholes (powering two ports) or five (powering one port). USB 3.0 headers, meanwhile, are more straightforward: They are a 20-pin rectangular grid that accepts a cable powering one or two USB 3.0 ports. You'll want to make sure any board you're buying has connectors that match what's on your PC case—and vice versa.
All three kinds of USB header, left to right: USB 2.0, USB 3.0, and USB 3.1 Gen2
Some of the very latest boards (from 2017 forward) may have a third kind of USB header, for USB 3.1 Gen2, which is meant for new, faster USB ports. Only a few PC cases, however, so far have a cable that works with this header. The header on the board looks like a cross between a regular USB Type-A port (it's rectangular) and an HDMI port (in that it has a protruding set of contacts in the middle).
Front-Panel Header
The front-panel header is a grid of pins on the motherboard, often with some color coding or other on-board labeling, that accepts wires from your PC case. To this set of pins, you'll connect the thin cables for the case's power and reset switches, as well as the hard drive activity and power-on LEDs (and, in some designs, an onboard speaker). Most of the time, the pins for each connector are in pairs; know that the polarity of the pairs doesn't matter for the switch cables, but it does for the LEDs. The motherboard manual will contain a schematic that shows where the header is and which pins power what.
Color-coded front-panel header on a Gigabyte/Aorus board
Some board makers, pioneered by Asus with its "Q-Connector," provide a small block that plugs into the front-panel pin header, covering it entirely, but with an identical pinout on top of it. This lets you plug in the appropriate wires outside the PC case, then plug in the connector as a whole.
Asus Q-Connector block
MOSFETs and Capacitors
A MOSFET (for "metal oxide semiconductor field effect transistor") is a type of transistor, that, in the context of computer motherboards, is used for voltage regulation.
A bank of MOSFETs (the cubes), fronted by a line of capacitors
From a nontechnical buyer's point of view, MOSFETs are not differentiating features, beyond a motherboard maker's claims of premium components. The actual components are often hidden beneath a passive heatsink to keep them cool during operation. The most frequently bandied set-apart feature among MOSFETs is a "low-resistance" design, sometimes denoted as RDS(on), which purportedly means less heat is generated.
As for capacitors, you'll see these electronic components scattered across a typical motherboard performing in a variety of subsystems, but their base function is to act as "holding pens" for electrical charge. Depending on where they are used, they can take on different shapes (though usually, little drums), sizes, and colors. As a buying consideration, they are relevant only insofar as the type of capacitor is sometimes heralded as a premium feature.
Run-of-the-mill capacitors are electrolytic, containing a small volume of material soaked with a liquid. Depending on the quality of manufacture and the expected lifespan, these kinds of capacitors can swell and leak over time, leading to board failure. The PC-enthusiast community generally rallies around Japanese-made electrolytic capacitors as a better bet for longevity, and motherboard makers tend to trumpet "Japanese capacitors" if they are present. (We can't verify how accurate this longtime claim is, however.) Solid-state capacitors, on the other hand, are immune to leakage and thus preferred.
AAFP/HD Audio (Front Audio Header)
Just about all PC cases have a headphone and microphone jack that terminates, inside the case, in a cable with a 10-pin header connector. This plugs into a pin grid on the motherboard called an "HD Audio" header. In a nutshell, HD Audio brings auto-detection functionality to the ports, allowing the system to sense the presence of devices plugged into the ports and behave accordingly. The pin header is sometimes labeled on the motherboard as "AAFP," for the "analog audio front panel" cable.
For your case's audio cable: 10-pin AAFP header connection (one pin is missing for keying)
In earlier times, this connector on the board was often an "AC '97" header, and during the transition time between the two, some motherboards provided a selector in the BIOS to let you switch the operation of the board's audio silicon between the AC '97 and HD Audio modes. (The pin connector is physically the same.) In some older PC chassis, you may have a forked cable for the audio ports with connectors for both HD Audio and AC '97. Ignore the latter. And with a new motherboard and case, you'll definitely be using the former connector, as HD Audio is the current standard. That's the only one of the two you need to know nowadays.
Serial ATA
Serial ATA, often abbreviated to SATA, is the standard interface for drives inside consumer and business PCs. It's employed by hard drives, SSDs, and optical drives alike. Drives with a SATA interface will have both a SATA data connector (which connects, in a desktop PC, to one of the SATA ports on the motherboard) and a wider, blade-like "SATA-style" power connector (which connects to a SATA power lead coming from the power supply).
A bank of edge-mounted Serial ATA connectors
The SATA interface itself has speed grades, notably SATA 2 and SATA 3, variously called "SATA II"/"SATA 3Gbps" or "SATA III"/"SATA 6Gbps," respectively. These indicate the maximum data transfer rate possible with an attached drive. To gain the maximum throughput benefit, both drive and motherboard must support the same SATA spec, but any new motherboard and drive you'll be considering these days will support SATA 3 exclusively. SATA 2 will come into play nowadays only in legacy gear.
Note that on a given motherboard, some of the SATA ports may be handled by different controller chips, possibly meaning different capabilities. (For example, some of the SATA ports may support RAID, and others not.) The manual should explain any nuances among the ports.
24-Pin ATX Power Connector
If you've ever built a PC, torn down a PC, or upgraded a motherboard, you've tugged at the large power-supply cable plugged into this connector. A bulky receptacle with two rows of 12 pins, this connector is the main power source for your system, accepting the by-far-biggest power cable coming off a desktop PC's power supply.
This is your motherboard's main power feed
The 24-pin ATX is now a standard connector at the motherboard end. At a transition time in the mid-2000s, many power supplies started showing up with ATX power connectors that were split into 20-pin and four-pin portions that could snap together. (That's because older boards required just the 20-pin connection; the additional four pins added extra circuits at different voltage levels.) Many modern power supplies still split the 24-pin connector into these two pieces as a compatibility sop to these older board designs.
"+12V" CPU Power Connector
On modern motherboards, the CPU power connector is a dedicated four-pin (two by two) or eight-pin (two by four) power connection, usually positioned near the actual CPU socket. A matching cable from any recent-model PC power supply will fit in here—the cable will often be labeled "CPU power."
The eight-pin version of the CPU power connector on an Asus board
The connector provides a power source separate from the main 24-pin connection, and is at times referred to as a "+12V" connection. This and the 24-pin ATX connector aren't really shopping concerns on the motherboard end if you're looking at new boards (pretty much any modern motherboard will have these), but they are connections to account for on your PC's power supply if you're transplanting or reusing a power supply that's older.
PWM Fan Header
A cluster of four pins to which you connect a chassis fan. Motherboards typically come studded with these, the more the larger the board. The PWM header allows for fine control over fan speeds based on temperature guidelines that are set at a system level. The header sends a 12-volt current through one pin to power the fan, while a control signal on another pin tells the fan the amount of current to draw, regulating the speed (thus PWM, for "pulse width modulation").
Two four-pin PWM fan headers off to the right
You'll want to be sure that a motherboard you're choosing has enough of these headers to accommodate the fans in your chassis. Some case fans will have only a three-pin connector; you can plug these into a four-pin header, but you won't get the speed control.
M.2 Slots and U.2 Ports
Many motherboards from the last couple of years have adopted a new type of slot, dubbed M.2, used with an emerging form factor of solid-state drives and certain other components. M.2 drives are much smaller than traditional SSDs. They are shaped like gumsticks and come in a variety of lengths, indicated by a numeric code in their names. (M.2 Types 2242, 2260, and 2280 are 42mm, 60mm, and 80mm long, respectively.)
An M.2 slot banded in red, with multiple mounting points for 2242, 2260, and 2280 drives.
Most of the M.2 devices of interest to PC builders and upgraders will be SSDs, but it's also possible to find wireless (Wi-Fi) cards in the M.2 format. (See our picks for the best M.2 solid-state drives at the link.) You'll want to know what lengths of M.2 device a board supports if you're looking to outfit your PC with such a drive. Most new boards have at least one M.2 slot, with some offering two. Compact or space-constrained boards may have an M.2 slot on the back of the board. Also, some boards provide thermal solutions that screw down or snap over the M.2 drive(s) to keep them running cool.
"M.2 Shield" thermal solution over an M.2 slot
Much less common than M.2 is the U.2 port, which resembles a bulky SATA port and is used by a select few enterprise-grade storage devices, such as the Intel 750 Series SSD . You'll see it here and there on high-end motherboards. It isn't a must-have feature, by any means, but it's good to know why it's there.
RGB and RGBW Headers
Dedicated on-motherboard RGB headers have emerged in the last couple of years, as RGB mood lighting has invaded the motherboard itself and now extends to light strips that you can snake around your PC case's interior. These headers use a four- or five-pin connection, much like a case-fan header, to which you can connect discrete LED strips. Ordinary RGB headers have four pins, while their RGBW variant uses five pins. The RGBW headers provide for purer whites in the lighting and work with specific RGBW strips; these headers should also accept the four-pin strips if that is what you have, but check the manual for details.
An RGBW five-pin header; you can plug in four-pin strips, too
To control the patterns and colors, RGB headers (and any RGB lighting built into the boards themselves) work with software solutions provided by the motherboard maker. Each major maker has its own, including Asus (Aura Sync), Gigabyte (RGB Fusion), and MSI (Mystic Light).
CMOS, CMOS Battery
CMOS stands for "complementary metal-oxide-semiconductor." It's a chunk of memory on a system motherboard that holds the BIOS and its settings, as well as maintaining the system clock settings.
To retain its settings with the system powered off or unplugged for long periods, an onboard battery keeps the CMOS juiced up. In modern motherboards this battery is almost always a CR2032 coin cell.
Debug LED
Common on premium motherboards, the debug LED is an exceptionally handy feature for nonveteran PC builders and pros alike. A (usually two-digit) readout, it shows off error codes if the PC fails to boot. The codes, outlined in the board manual, can help you pinpoint the reason for a failed boot sequence, such as RAM that is installed improperly or a video-card error.
(Have suggestions for more terms we should add? Chime in below in the comments section below.)
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