ATX, MicroATX, Flex.. Difference?

[goofy2000]

What's the difference between ATX vs Micro ATX vs Flex form factors?
What kind of dimension a case should have to be able to house all 3 from factors board...?

 

[Jhhnn]

ATX is larger with more expansion slots than MATX, which is larger than the FLX boards. In general, ATX cases will accomodate the smaller MATX boards, but not vice-versa. At least some MATX cases will accomodate FLX boards, I really don't know if FLX boards will fit in ATX cases.

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