How can you tell if your case is ATX or mATX?

I want to upgrade my power supply in a HP Pavilion a6323w duel core. On my power supply it says Bestec ATX250-12z





thank youHow can you tell if your case is ATX or mATX?
Easy, ATX refers to a computer that looks like a normal desktop, no smaller than maybe 2 feet tall and half a foot wide or so. If you have a case that looks more like a small box or like a server computer, you are probably needing a mATX PSU. Best to take your PSU out and take it with you when you go, or refer to it when shopping online.