NonATX

nonATX is a descriptive term used to refer to computer hardware that does not conform to the standard ATX form factor. It is not an official standard, but a way to group a variety of alternative motherboard sizes, layouts, and related components that differ from ATX in one or more ways, such as dimensions, mounting hole patterns, or I/O shield size.

Common examples of nonATX form factors include microATX (smaller than ATX and widely used in mainstream desktops) and Mini-ITX (even smaller, popular for compact builds). Other ITX-related variants such as Nano-ITX and Pico-ITX exist for very compact systems. Larger nonATX options include extended or oversized boards such as E-ATX and XL-ATX, which depart from ATX dimensions in order to accommodate more RAM slots or PCIe lanes. In practice, "nonATX" also covers proprietary or OEM-specific board footprints used in certain desktops, servers, or embedded systems.

NonATX is frequently associated with nonstandard chassis and power-supply combinations as well. For example, small form factor (SFX) power supplies are designed for compact cases and ITX-class motherboards, while some non-ATX cases may use different mounting schemes or back-panel layouts.

Compatibility is the main consideration when building with nonATX components. Cases, power supplies, and cooling solutions must be chosen to match the board’s form factor and mounting points, and I/O shield and PCIe slot alignments may differ from ATX expectations. NonATX offerings enable a range of use cases from compact home builds to high-end, multi-GPU workstations, but they require careful matching of parts.