The ATX motherboard comes in four different types with different sizes and configurations. All four kinds of ATX motherboards are available: ATX, also known as Advanced Technology eXtended, (E-ATX), also called Extended ATX, Micro ATX, and Mini ITX. It is possible to use ATX, MATX, and ITX cases, but not the EATX case as it is quite large. In terms of reliability and decent performance, ATX is a good alternative for a compact PC build with an equivalent case size to support the rated components. Widest extended ATX format (12 x 10.7) with 305 * 272mm diameter. In Diameter) ATX width: (12 * 9.5) Under 305 * 244 mm in diameter (Most Popular) Micro ATX: (9.6 * 9.5) Under 244 * 244 mm in diameter (Ideal for Small Builds) Mini ITX width: (6.7 x 6.7) Under 170 x 170 mm in diameter (Most Compact)