I want to upgrade RAM in my Asus x550CA xx545D/(with DOS) '''but unable to detect whether it has one additional free RAM slot or not''' . If available, I would like to know what type of Ram is installed in this laptop( i.e voltage- 1.35V or 1.5V?) so that I can buy appropriate Ram stick to make it 4gb. I understand that it can support upto 10GB.