I did not keep the original post to this thread, but I believe that the question mentioned the installation of "third-party RAM chips" and the fact that Apple would require the removal of ALL of the installed RAM under Apple's waranty policy. I felt that the responses that I was reading were not paying attention to the Apple policy of requiring the removal of non-Apple RAM for warranty work to be performed. Also, the cost of Apple RAM is so exorbitant that I never use it except for the original OEM parts. As to the vendor question, I have purchased many RAM chips from Data Memory Systems and have had nothing but exemplary service from the company (www.Datamem.com). They replaced two sets of chips for a non-Apple laptop that I was upgrading. This required that they mail two boxes to me with RMAs for the return of the non-fitting chips. They did this without any additional charges and used two-day service each time.