Find out we have a 32bit or 64 bit intel based MAC

  1. Choose About This Mac from the Apple () menu in the upper left menu bar, then click More Info. 

            2. And click System Report in OverView Tab.,

            3. And Open the Hardware section see the Processor name 

    4. 

1. Compare your Processor Name to information below to determine whether your Mac has a 32-bit or 64-bit processor.

Processor Name	32- or 64-bit
Intel Core Solo	32 bit
Intel Core Duo	32 bit
Intel Core 2 Duo	64 bit
Intel Quad-Core Xeon	64 bit
Dual-Core Intel Xeon	64 bit
Quad-Core Intel Xeon	64 bit
Core i3	64 bit
Core i5	64 bit
Core i7	64 bit

reference : http://support.apple.com/kb/ht3696