Which motherboard form factor is most commonly used in full-sized personal desktop computers?

The ATX form factor is considered the industry standard for full-sized personal desktop computers. Developed by Intel in 1995, ATX boards typically measure 305 mm x 244 mm (12 in x 9.6 in) and provide ample space for multiple expansion slots and connectors, allowing for a wide range of hardware configurations. This versatility makes it the preferred choice for desktops, as it supports more RAM slots, PCIe slots, and additional storage options compared to other form factors.

In contrast, MicroATX and Mini-ITX boards are designed for compact builds and typically have fewer expansion slots and features, which may not meet the requirements of users who need a more powerful, expandable desktop system. While BTX was an alternative design aimed at improving thermal performance, it has not gained widespread adoption and is not commonly found in modern systems. Thus, ATX remains the most prevalent form factor in standard desktop computers, making it the best answer.