You could also go to Use the Crucial System Scanner software to find out what type of memory is in your computer
and run the scanner, it will tell you what memory you would require: Example:
Run the scanner:
It will then give you an overview and advise what is compatible on the left:
It will also give you upgrade options if you click the link on the right that says 'View Quick Configurations'
This may help determine if the memory you have is compatible or help upgrade in the future.