Different types and capacities of memory are available for various Mac models. The memory prices have been dropping as production has made them more available.
How Much RAM Can You Install?
The newer “Unibody” MacBook Pro with the black bezel model can run up to a maximum of 8GB DDR3-1066 memory.
However, previous MacBook Pro “Aluminum” versions can only run 6GB maximum.
The Mac Pro can support up to 32 GB of DDR3 memory. More is better.