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Almost all OEM cases only support mATX (uATX) MOBO's, some even don't conform, but you can measure for yourself; see -> http://en.wikipedia.org/wiki/ATX
note the side column. If you MOBO is square 9.6 in (244 mm) x 9.6 in (244 mm) then it's mATX.
Full ATX is 12 in (305 mm) x 9.6 in (244 mm).