Most computers that are sold feature a standard form factor motherboard. The use of standards in this way helps to ensure that any components are compatible, rather than requiring the user to dive deeply into the specification of every component and its mounting mechanism to verify compatibility.
The original motherboard standards were the XT and AT standards used in the original IBM PCs of the same name in 1983 and 1984, respectively. In 1995 these standards were replaced by an Intel-developed standard, ATX, that is still used today.
Some system integrators or OEMs (Original Equipment Manufacturers) such as DELL have generally chosen to avoid using standard motherboard form factors. To some degree, this has enabled alternative layouts that can be more space efficient or improve airflow. However, the primary driving factor and effect is that the motherboard and many connectors used are proprietary, tying the owner into official repair, replacement, and upgrade services.
While this behavior might not be an issue in a corporate environment, companies will likely already have a service contract with the PC manufacturer. It is less friendly towards the standard home user. The driving concept of the proprietary form factor is demonstrated by the use of non-standard connectors. It would be more believable that the changes are purely for space or efficiency reasons if standard connectors were used.
ATX
The ATX motherboard standard has been in place since 1995. While the individual components have changed as technology and connector standards have changed, the overall average hasn’t changed. For example, the motherboard still uses the same standard size of 305mm x 204mm. Another critical point is the mounting points. As the screw hole locations are standardized and unchanged, you could fit any modern ATX motherboard into a 1995 ATX compatible case. Or a 1995 ATX motherboard into a modern case with no issues.
The ATX standard defines the location of the CPU socket, RAM sockets, PCIe expansion slots, chipset, some power connectors, and the rear I/O. This standardization means that any compatible PC case will fit any ATX motherboard. For example, users don’t need to check if the rear I/O plate is too large. It also means that other components will just fit. For instance, A GPU will fit and align with the rear access panel. Large components like the CPU cooler can be designed to allow for the proximity of the RAM. In this case, many large CPU coolers simply warn users that they may impact compatibility with large RAM heat sinks.
ATX Variants
A variant of ATX called MicroATX is available that is 244mm x 244mm making it roughly 75% of the height of the standard ATX motherboards. This is generally used in small form factor computers. These might be secondary computers inside large computer cases or used in low-load environments such as a media streaming computer.
The reduction in size does mean some components need to be sacrificed. Typically, these are PCIe expansion slots. The smaller size also somewhat limits the cooling capacity that might be achievable in a more significant case. A key difference of MicroATX is that the motherboard mounting screws have different locations. Some but not all full-size cases offer secondary mounting points for MicroATX motherboards.
EATX is a relatively loosely defined standard that simply covers motherboards that are larger than standard ATX motherboards. A key point is that the mounting points are the same as for ATX motherboards. Care should ensure that cases offer enough space to fit the larger EATX motherboards. Typically, one of the core differences of an EATX motherboard is the presence of the second set of RAM slots on the other side of the CPU socket. Some EATX motherboards may offer dual CPU sockets.
ITX
There are three ultra-small form factor motherboard standards: MiniITX, NanoITX, and PicoITX. These are compatible with x86 CPUs and could be used for small form factor computers. However, these are typically used in industrial and automotive control systems. Components are generally chosen for thermal performance reasons, often allowing operation under passive cooling, especially with the case being designed as a passive radiator.
Conclusion
ATX has been the standard motherboard form factor for PCs since 1995. It standardizes the size and mounting points of the motherboard as well as the location of principal components to ensure compatibility between the motherboard and other components and the motherboard and PC cases.
Some smaller and larger variants are also standardized, enabling users with more specific use cases to have greater choice. Some OEMs choose not to use standard form factors. Or even connectors, primarily as a method of tying buyers into their ecosystem of repair, replacement, and upgrade services, exemplifying the need for such standards. Don’t forget to share your comments below.
