What is the Difference Between AT and ATX? Explained in Detail

When building your own computer or upgrading an existing one, there are a lot of things to consider. One of them is the type of motherboard you need. Two common types of motherboard are AT and ATX. You might have heard these terms thrown around, but what do they actually mean? And what’s the difference between them?

Let’s break it down. AT stands for Advanced Technology, and it was the first form factor for motherboards. It was introduced in the 1980s and became the most popular type of motherboard until the late 1990s. AT motherboards are characterized by their size – they’re relatively big and bulky compared to modern motherboards. They also have a specific layout that can make it difficult to access some of the components.

On the other hand, ATX stands for Advanced Technology Extended. This type of motherboard was introduced in the mid-1990s and quickly became popular because it addressed some of the issues with AT motherboards. ATX motherboards are smaller than their predecessors, making them more suitable for smaller cases. They also have a more intuitive layout that makes components easier to access. There are other differences between the two types of motherboard, and we’ll explore those in more detail later on.

AT and ATX: An Introduction

When it comes to computer motherboards, the two most common designs are AT and ATX. These two designs both serve the same purpose – to connect all the components of the computer together – but they do so in very different ways.

The AT design, or Advanced Technology, was the original motherboard design introduced in the 1980s. It quickly became the standard for personal computers, but it had some limitations that eventually led to its replacement by the ATX design.

The ATX design, or Advanced Technology Extended, was introduced in the 1990s to address the limitations of the AT design. It quickly became the new standard for personal computers and is still in use today.

Key Differences Between AT and ATX

  • Size: The AT design is much larger than the ATX design, measuring 12 x 13 inches compared to the standard ATX size of 9.6 x 12 inches.
  • Power Supply: The AT design uses a single 6-pin power connector, while the ATX design uses both a 20- or 24-pin power connector and a 4-pin auxiliary connector.
  • Expansion Slots: The AT design has only a few expansion slots, while the ATX design has many more, allowing for greater flexibility in adding components.

Advantages of ATX

There are several advantages to the ATX design that make it a better choice for modern computers:

  • More Expansion Slots: The ATX design allows for more expansion slots to add components, such as extra graphics cards and network adapters.
  • Better Cooling: The ATX design allows for better airflow and cooling of the components, which can help to extend the life of the computer.
  • Remote Control: Some ATX motherboards allow for remote control of the computer, which can be useful for troubleshooting and maintenance.


While the AT design was a groundbreaking innovation at the time, the ATX design has since become the standard for modern computers. The key differences between the AT and ATX designs, such as size, power supply, and expansion slots, have led to the ATX design being more versatile and better suited for modern computing needs.

Size12 x 13 inches9.6 x 12 inches
Power SupplySingle 6-pin connector20- or 24-pin connector, and 4-pin auxiliary connector
Expansion SlotsFewMany

As technology continues to evolve, there may be new motherboard designs that surpass the ATX in terms of performance and functionality. However, for now, the ATX design remains the most popular and widely used motherboard design for modern computers.

Understanding the Form Factor of Motherboards

When it comes to building a PC, the form factor of your motherboard is an important factor to consider. The form factor is essentially the size and shape of the motherboard, and it determines what type of case you can use and what components are compatible.

In general, motherboards come in two common form factors: AT and ATX.

AT vs. ATX

  • The AT (Advanced Technology) form factor was the standard for motherboards in the 1980s and 1990s. They were larger and less efficient compared to modern motherboards.
  • The ATX (Advanced Technology Extended) form factor was introduced in 1995 as a more efficient alternative to the AT form factor. ATX motherboards have a smaller form factor and can support more features.
  • One key difference between AT and ATX motherboards is the position of the power connector. AT motherboards have a power connector on the side of the board, while ATX motherboards have it in the center.
  • Another difference is the number of expansion slots. ATX motherboards typically have more expansion slots than AT motherboards, allowing for more devices and components to be connected.
  • ATX motherboards have also been designed with better cooling capabilities, allowing for more efficient heat dissipation.

Other Form Factors

While AT and ATX are the most common form factors, there are other form factors available, including:

  • Mini-ITX, which is a smaller form factor designed for compact PCs.
  • Micro-ATX, which is a slightly larger form factor than Mini-ITX and can support more components.
  • Extended ATX (EATX), which is a larger form factor designed for high-performance systems and can support multiple CPUs and GPUs.


In summary, the form factor of your motherboard is an important consideration when building a PC. ATX motherboards have become the standard due to their efficiency, cooling capabilities, and ability to support more components. However, there are other form factors available depending on your specific needs and requirements.

Form FactorSizeFeatures
ATFull-sizePower connector on the side of the board; fewer expansion slots
ATXSmaller than ATPower connector in the center of the board; more expansion slots; better cooling capabilities
Mini-ITXSmaller than Micro-ATXDesigned for compact PCs
Micro-ATXLarger than Mini-ITXCan support more components
EATXLarger than ATXDesigned for high-performance systems; can support multiple CPUs and GPUs

By understanding the different form factors available and their features, you can choose the one that best suits your needs and build the perfect PC for your requirements.

The AT Standard: Pros and Cons

The AT (Advanced Technology) standard was the first widely used motherboard configuration in the personal computer industry. This standard was introduced in 1984 and was used until the mid-1990s, when it was replaced by the ATX (Advanced Technology Extended) standard. While the AT standard was revolutionary at the time, it had its fair share of pros and cons.

  • Pros:
  • The AT standard was the first motherboard configuration that allowed for expansion slots to be placed in parallel instead of perpendicular to the board. This made it easier to add peripheral devices such as sound and video cards to the system.
  • The AT standard also standardized the placement of the keyboard and mouse ports on the back of the computer case. This made it easier to connect these devices to the system.
  • The AT standard was also the first configuration to use a power supply that could be switched on and off by the system. This allowed for power consumption to be managed better and reduced the risk of damage to the system due to power surges.

The AT Standard: Pros and Cons

Despite the many advantages of the AT standard, there were also several drawbacks:

  • Cons:
  • The AT standard used a larger form factor than today’s motherboards, making it more difficult to fit into smaller computer cases.
  • The location of the power supply in the AT standard also made it difficult to access and replace, especially in smaller cases.
  • The AT standard had limited support for plug and play devices, which meant that peripherals and other devices had to be manually configured.

The AT Standard: Pros and Cons

The AT standard was an important stepping stone in the evolution of computer motherboards. While it may not have been perfect, it paved the way for more advanced standards such as the ATX. Today, the AT standard is rarely used, but it still holds a place in the history of computer hardware.

AT StandardATX Standard
Introduced in 1984Introduced in 1995
Used a larger form factorUsed a smaller form factor
Expansion slots perpendicular to boardExpansion slots parallel to board
Location of power supply made it difficult to replacePower supply location makes it easier to replace

As you can see, the ATX standard addressed many of the drawbacks of the AT standard. It introduced a smaller form factor, expansion slots placed parallel to the board, and a power supply location that made it easier to replace. All in all, the ATX standard improved upon the AT standard in nearly every way.

The Advantages and Disadvantages of ATX

ATX and its successor, microATX, are the most popular motherboard form factors today. While AT was once widely used, its bulkiness and lack of expandability led to its decline. In this section, we’ll discuss the advantages and disadvantages of the ATX form factor.

  • Advantages:
    • Better airflow: ATX cases are generally larger than microATX or mini-ITX cases, which allows for better airflow and cooling. This is especially important for high-performance systems that generate a lot of heat.
    • More expansion slots: The ATX form factor allows for up to seven expansion slots, which provides ample room for adding extra components like graphics cards, sound cards, and other add-on cards.
    • Easier to work with: ATX motherboards are typically easier to work with than their smaller counterparts. They have more space between components, making it easier to install and remove hardware.
    • More power: ATX power supplies are generally more powerful than those used in microATX or mini-ITX systems, which makes them ideal for high-end gaming or workstation PCs.
  • Disadvantages:
    • Larger size: ATX motherboards and cases can be quite large, which can be a problem if you have limited desk space or plan to build a system for use in a small form factor case.
    • Higher cost: ATX motherboards and cases are generally more expensive than microATX or mini-ITX counterparts due to their larger size and increased complexity.
    • Higher power consumption: ATX systems typically consume more power than smaller form factor systems, which can result in higher electricity bills over time.
    • More difficult to transport: Due to their larger size and weight, ATX systems can be more difficult to transport than their smaller counterparts.


While the ATX form factor has its advantages and disadvantages, it remains the most popular choice for building high-performance desktop PCs. If you need plenty of expansion options, better cooling, and more power for demanding applications, an ATX system is definitely worth considering. On the other hand, if you have limited space, a smaller budget, or don’t need all the extra features, a microATX or mini-ITX system may be a better fit.

Better airflowLarger size
More expansion slotsHigher cost
Easier to work withHigher power consumption
More powerMore difficult to transport

Ultimately, the choice of form factor depends on your specific needs and preferences. By weighing the pros and cons of each option, you can make an informed decision and build a system that meets your requirements.

Compatibility Issues between AT and ATX Motherboards

When upgrading or building a PC, one of the critical components to consider is the motherboard. It serves as the backbone of the whole system, connecting all the other parts together. There are two main types of motherboards that are commonly used – AT and ATX. While they may look similar, there are notable differences that can cause compatibility issues when interchanging components. Here is a closer look at some of the compatibility issues that arise when dealing with AT and ATX motherboards:

  • Power Supply Unit: One of the most significant differences between AT and ATX motherboards is the power supply unit (PSU) connection. AT motherboard’s PSU has two distinct connectors: one that provides the primary voltage, and the other that provides the secondary voltage. However, ATX motherboards use a single connector that provides all the necessary voltage requirements. So, if you’re planning to upgrade an AT system to ATX, you’ll need to replace the power supply since it won’t be compatible.
  • Case Compatibility: AT and ATX motherboards also have different screw hole patterns and sizes, which means that they are not interchangeable in terms of fitting into a particular PC case. Consequently, when building or upgrading a PC, it is essential to ensure that the motherboard you’re getting is compatible with the case you have or the case that you plan to purchase.
  • Expansion Slots: Expansion slots on ATX motherboards are placed differently, resulting in incompatibility with AT systems. The ATX standard has longer expansion slots than the AT, which means that AT expansion cards will not fit in an ATX motherboard, and vice versa.

It’s always wise to ensure that the components you’re purchasing are fully compatible with each other, and that is no exception when it comes to motherboards. The above compatibility issues highlight some of the most significant concerns to consider when dealing with AT and ATX motherboards.

Below is a summary table for quick reference:

Compatibility IssuesATATX
PSU ConnectionTwo distinct connectorsSingle connector
Case CompatibilityDifferent screw hole patterns and sizesDifferent screw hole patterns and sizes
Expansion SlotsShorter expansion slotsLonger expansion slots

Understanding the compatibility issues between AT and ATX motherboards is crucial in ensuring that your PC components work together seamlessly. Always do thorough research before you purchase, and ensure that you have compatible parts.

Upgrading from AT to ATX: What You Need to Know

When upgrading from the AT standard to the ATX standard, there are several important factors to consider. Here, we will discuss one of the most critical aspects of the upgrade: power supply compatibility.

  • AT vs. ATX Power Supplies
  • One of the most significant differences between AT and ATX power supplies is the size.

    The AT power supply measures approximately 6 x 5.5 x 3.5 inches while the ATX power supply measures approximately 5.9 x 3.4 x 5.5 inches.

    Aside from size, there are other differences to note:

    FeatureAT Power SupplyATX Power Supply
    Soft PowerNoYes
    Power SwitchMechanical (Hard)Soft

    These differences are crucial because they affect the compatibility between a new ATX motherboard and an existing AT power supply.

  • AT to ATX Power Supply Upgrade
  • If you are upgrading from an AT to an ATX motherboard, you will need a new power supply to support the additional power requirements of the new motherboard.

    The easiest way to determine if your current power supply is compatible with a new ATX motherboard is to check the motherboard manual or manufacturer’s website for the ATX power supply requirements. If your current power supply meets these requirements, it may still be compatible.

    However, if your current power supply doesn’t meet the requirements for the new ATX motherboard, you will need to purchase a new power supply compatible with the ATX standard.

Custom ATX Builds versus Pre-Built AT Systems

When it comes to building your own ATX computer, you have complete control over the hardware you choose to include. It is an excellent option for those who have specific needs such as gaming, video editing, or heavy-duty tasks. A custom ATX build allows you to tailor your computer to your needs, so you’re not paying for any unnecessary parts. Moreover, you can easily upgrade components when new hardware releases.

On the other hand, a pre-built ATX system comes ready to use out of the box. It is excellent for those who don’t have much technical knowledge in computer hardware. Pre-built systems are becoming more affordable these days, and they are also an excellent option for those who want a simple, plug-and-play computer.

  • Custom ATX Builds:
    • Complete hardware control
    • Better performance and efficiency
    • Easier to upgrade
    • Cheaper
  • Pre-Built AT Systems:
    • Convenient and time-saving
    • No technical knowledge needed
    • Warranty and support included
    • Ready to use out of the box

Ultimately, the decision of whether to go for a custom build or a pre-built system depends on your needs and budget. A custom build can be a great investment for those looking to do heavy-duty tasks or gamers who want the best graphics and performance. In contrast, a pre-built system can be an excellent option for those who want a simple, basic computer for everyday use.

Below is a table that highlights the differences between custom ATX builds and pre-built AT systems:

Custom ATX BuildsPre-Built AT Systems
Hardware ControlComplete hardware controlNo hardware control
UpgradesEasier upgradesHarder upgrades
PriceCheaperMore expensive
ConvenienceTime-intensiveReady to use out of the box
Warranty and SupportNo warranty or supportWarranty and support included

What is the Difference Between AT and ATX?


1. What is AT? AT stands for “Advanced Technology” and refers to the first widely used form factor for motherboards and power supplies in personal computers. AT motherboards are rectangular, measuring 12 inches by 11 inches and require a power supply with a switch that controls the voltage input.

2. What is ATX? ATX stands for “Advanced Technology Extended” and is the newer form factor for motherboards and power supplies in personal computers. ATX motherboards are also rectangular, but measure 12 inches by 9.6 inches and are designed to improve airflow and ease of use. ATX power supplies have a single 20- or 24-pin connector to power the motherboard, while providing multiple connectors for other components.

3. Can I use an AT power supply with an ATX motherboard? No, AT power supplies and ATX motherboards are not compatible due to differences in voltage and wiring. Using an incompatible power supply can damage the motherboard or other components.

4. What are the advantages of using an ATX motherboard? ATX motherboards offer several advantages over AT motherboards, including better airflow, easier cable management, and support for modern hardware components like USB and PCI Express.

5. Can I use an ATX power supply with an AT motherboard? Yes, it is possible to use an ATX power supply with an AT motherboard, but an adapter may be required to convert the 20- or 24-pin connector to the 12- or 9-pin connector needed by the motherboard.

Closing Thoughts

Thank you for taking the time to learn about the difference between AT and ATX. While AT motherboards were once the standard, the improved features provided by ATX motherboards have made them the more popular choice today. As technology continues to evolve, it’s important to stay informed about the latest developments in computer hardware. We hope you’ll visit again soon for more informative articles and updates.