How to find out what memory you have in your Linux box (size, configuration, max RAM, speed)
Summary: use dmidecode
I needed to buy some RAM for my low cost HP server and needed to know how much was in it, what speed it was, how many banks were free and what was the total amount of memory I could put in. It turned out that dmidecode was alread installed on my CentOS box, and it gave all that information, among much else.
I did a lot of searching etc and eventually came across dmidecode, you just run it as root and it parses through /dev/mem and loads the DMI tables, parses them and prints them in human readable form.
Physical Memory Info under Linux - R.I.Pienaar - www.devco.net
lshw also gives memory information.