What Does ATX Stand For In A Motherboard?

CG Director Author Christopher Harperby Christopher Harper   /  Published 

What does ATX stand for in a Motherboard, and why should it matter to you?

In this article, I’m going to make sure you know the answers to those and related questions- so without further ado, let’s start your crash course on ATX.

What is ATX?

ATX stands for Advanced Technology eXtended and refers to a form factor used by PC motherboards, cases, and power supplies.

I’ll be breaking down the meaning of each in its specific context in this article, as well as a few follow-up questions about related standards and prominent ATX cases currently available on the market.

What does ATX Stand For In A Motherboard?

In the context of a motherboard, the form factor ATX defines the dimensions, mounting holes, I/O panel size, as well as the power and PC case connectors of a motherboard.

A full-sized ATX Motherboard is 12 by 9.6 inches (30x24cm) and while there are bigger and smaller Motherboards, these are defined through a different standard, as shown below:

Motherboard Size Comparison Chart

Motherboard Size Comparison Chart – XL-ATX, E-ATX, ATX, M-ATX, ITX

Even though they could technically fit 6-7 PCIe slots, ATX-sized motherboards usually offer about two x16 PCI Express slots, and an additional two x4 or x1 PCIe slots. These PCIe slots are sometimes replaced by M.2 storage slots on modern motherboards. (Since NVMe M.2 drives use PCI Express’ faster bandwidth.)

Adding 6-7 PCIe Slots onto an ATX motherboard wouldn’t make much sense, because they would be limited by the CPU’s and Chipset’s amount of PCIe-Lanes. You can read all about PCIe-Lanes in our in-depth article here.

ATX Motherboard Specifications

Source: ROG ASUS

An ATX Motherboard typically comes with 4x RAM Slots.

Let’s talk about the other two closely related definitions of ATX: Case ATX and Power Supply ATX.

What ATX Stands For in a Case

In a PC case, ATX still refers to the ATX motherboard standard, but now there are several modifiers attached to it.

You’ll see terms like ATX Full Tower, ATX Mid Tower, ATX Mini Tower, etc. These will all be describing varying form factors of PC cases that can fit ATX motherboards and their expansion cards.

PC Case Size Comparison

On average, these will still veer much larger than cases that are built exclusively for smaller Micro ATX and Mini ITX motherboards.

One thing worth noting is that Micro ATX is a separate standard, not a special ATX form factor. The giveaway there will be a cut-down on expansion slots and motherboard length,

What ATX Stands For In a Power Supply

In a Power Supply, ATX generally refers to a standard size power supply made to fit into ATX cases as well as a specific pin order in its power cables that’ll be able to fit into its respective connector on an ATX motherboard (24-pin, 8pin CPU etc).

Generally, the distinction of size in PSUs won’t matter very much unless you’re building in a chassis that isn’t made for regular-sized power supplies- as many SFF (Small Form Factor) PC cases.

Even if a full ATX PSU can technically fit, sometimes you’ll be better off with a smaller SFX power supply to free up extra room for cable management in a tightly-confined chassis and improve airflow. This won’t usually be a problem in an ATX Tower case, though.

Other Prominent Motherboard Size Standards

Besides the core ATX standard, it is important you know at least a little about the other prominent standards.

Motherboard form factors

Source: ASUS

Here’s a brief overview:

Micro ATX

  • Cut down to 4 maximum PCIe Slots from (theoretical) 6-7, with the corresponding change in height
  • The same number of RAM slots (4) as ATX, usually

“Extended ATX”

  • The same number of maximum PCIe slots as ATX, since Extended ATX extends width rather than height. Extended ATX does NOT add PCI Express slots above 7.
  • Because E-ATX is often used for High-End Desktop CPUs (with a lot more PCIe-Lanes), though, you usually see more full-sized PCIe-slots on this kind of Motherboard size
  • Extended ATX motherboards are wider than standard ATX motherboards, however, and can enable Dual-CPU systems, as well as more than 4 RAM slot – Usually 8 for Quad / Octa Channel RAM layouts
  • “Extended ATX” isn’t actually a real standard. Various competing standards of various increased widths over standard ATX are currently competing in the market- it’s a little confusing, actually.

Above is Steve from GamersNexus, discussing the conflicting Extended ATX Standards

Mini ITX

  • Even more cut down from ATX than Micro ATX in height and expansion slots- now there is only one PCI Express expansion slot on the entire motherboard.
  • RAM slots have also been cut down from the standard ATX and Micro ATX 4 RAM slots to 2 RAM slots. This also means a reduction in width compared to Micro ATX and ATX, allowing for Mini ITX to fit into even smaller enclosures.

Why should you care about Motherboard Form Factors such as ATX?

Checking a motherboard’s form-factor already gives you a good idea of how big it is, and a ball-park of its PCIe-Slots and RAM Modules.

Matching your ATX Motherboard to an ATX PSU and an ATX Case will pretty much guarantee they’ll be compatible.

An ATX sized motherboard will have mounting holes in the correct location as your PC’s ATX case, and it shouldn’t be too wide to cover any cable-pass-throughs to the back of your case.

An ATX PSU will in turn make sure the 24-pin power and 8-pin cpu power connectors will be able to fit your ATX motherboard.

While there are tools such as PCPartPicker that’ll try their best to check for compatibility issues, a lot of times they are wrong.

Doing further research by using dimensions, looking at part pictures and going through compatibility lists on manufacturer website are a PC-Builder’s daily bread that can be made easier by knowing about form-factors such as ATX.


What are the Smallest ATX Cases?

If you want the full expansion capabilities offered by ATX motherboards but are still looking for something small, we have exactly the compromise for you.

Turns out a significant portion of the case market is tailored for that niche, and Jerry has already written a detailed guide on the best and smallest ATX cases on the market.

I recommend it if you want a compact case but still want, say, a multi-GPU or a multi-expansion card setup.

Is Mid Tower or Full Tower ATX Better?

Generally speaking, it depends on your needs and how well your chassis actually suits them.

If you end up getting a Full Tower ATX case and running a more-or-less standard configuration inside with a single expansion card, you’re most likely going to experience worse airflow than you would with a smaller Mid Tower case unless you spend more on fans.

However, if you’re looking to have lots of drives, expansion cards, or even liquid cooling, Full Tower cases offer more flexibility for these things.

Not to toot my own horn, but I’ve written a fairly detailed guide on the Mid Tower vs Full Tower topic already. If you want to learn more, consider that– otherwise, the above rundown should give you an idea of where to lean for now.

Over to You

And that’s it, for now!

I hope that this article taught you more about the ATX- sorry, Advanced Technology eXtended- standard! Feel free to contact us in the forums or the comments section below if you have any more motherboard-related questions, and consider telling me: what did you do with your first ATX build?

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Christopher Harper

I have been a passionate devotee to technology since the age of 3, and to writing since before I even finished high school.

These passions have since combined into a living in my adulthood and have made writing about PC Hardware very satisfying.

If you need any assistance, leave a comment below: it’s what I’m here for.


Also check out our Forum for feedback from our Expert Community.

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