It’s very easy to check if your processor is a 64 bit processor.
Go to About This Mac…
Click More Info…then System Report
Get your processor name (mine is Intel core i5)
If it’s an Intel Core Solo or an Intel Core Duo it’s 32 bit, if its a Core i3; i5; i7; a Xeon; or a Core 2 Duo it’s 64 bit!
So now you now to download the relevant versions of software (mySQL 64 bit in this instance)