microATX, also known as ATX (sometimes transliterated as mATX[1] or uATX[2][3] on online forums) is a small form factor standard for computer motherboards, with a maximum size of 244 Xmm 244 mm (9.6 inches x 9.6 inches), but some uATX boards can be as small as 6.75 inches by 6.75 inches or 171.45 millimeters by 171.45 millimeters[4]. The standard ATX size is 25% longer, at 305mm X 244mm (12″ wide x 9.6″ deep). Currently available microATX motherboards support CPUs from VIA, Intel or AMD. There are no known microATX motherboards for processor architectures other than x86 and x86-64. -Source