This can be confusing for the beginner or for casual user's not familiar with all the jargon. If you spend the money and go to all the trouble to open your machine it's a real disappointment if it doesn't work or if it's the wrong one. Many manufacturer's offer memory configurator's to take out the guess work on what to get. Here are some of them:
This helps eliminate errors and hassle of picking up the wrong one and having to return it. When doing a friends or clients computer I much rather make sure I get the right stuff especially when it's not my money I'm spending. It not only saves money it also provides quicker turn around and a more satisfied client(or friend). I hope this helps and thanks for coming by. Good luck!