A motherboard with form factor A is the standard motherboard size. The majority of the mobos belongs to this category. You can place an ATX motherboard into a mid-tower or full-tower gaming PC, for example, and there'll be enough space for various components. ATX is larger than micro ATX and mini ATX, which offers more options than these smaller form factors. You can place up to 128GB of RAM on the motherboard, and 2 or more M.2 SSDs, depending on the chipset you choose.