ATX

PC Builds

The most common desktop form-factor standard, defining the size and mounting-hole layout of a motherboard (and the cases and power supplies built around it). Full-size ATX boards offer the most expansion slots and connectors; the smaller Micro-ATX and Mini-ITX variants trade some of those slots for a more compact build. Cases are rated for the board sizes they accept, and a case generally fits its own size and smaller — an ATX case usually takes Micro-ATX and Mini-ITX boards too, but not the reverse. Concrete example: a Mini-ITX board fits an ATX case, but a full ATX board won't fit a Mini-ITX case. Buying impact: pick the form factor first, since it sets how compact the PC can be and how much room you have to expand later.