There are no similar form factors to ATX if you're talking about a slimline. Slimline form factors are NLX and LPX. The form factors to ATX are BTX, Micro-ATX, and Flex-ATX. There is no correlation between slimline and ATX.
ATX is the form factor.
ATX
its similar to an LPX motherboard .. but its smaller .. the LPX was designed to be slimline the ATX is designed to be mini ... i actually dont know im just guessing .. its a computer .. use it .. quit yapping
ATX is the form factor which Motherboards, Computer Cases and Graphics Cards use to standardise sizing. An ATX form-factor Motherboard will fit an ATX Case, and an ATX Graphics Card will fit in the case as well.
ATX
ATX is a form factor. It does not dictate a specific chipset; anything from the now ancient 440BX to a Q57 can be used in an ATX system.
ATX is simply a form factor. A manufacturer can easily place legacy ports, connectors, and slots on an ATX motherboard.
MicroATX
A full ATX offers more flexibility than a Micro ATX or a Mini ATX.
MB is ATX form factor.
ATX (Advanced Technology Extended) is a combination of standards for computer system power supplies and chassis dimensions. It was developed as a replacement for the once-common AT form factor.