For small footprint and mobility! Also called: Flex-ATX form factor, small form factor (SFF), and book-sized PC. They are different from Micro ATX in that they often have only one 5.25" bay. Most FlexATX / Small Form Factor cases accept MicroATX / FlexATX and MiniITX motherboards. However, some SFF cases do require special motherboards and as such are only sold as Barebones with an included motherboard. For convience, we have indexed these into another section.