Linux / Unix: Find Out Maximum RAM Supported By The Server BIOS and Motherboard

How do I find out the maximum RAM supported by the Dell / HP / IBM / Oracle / Sun / Intel / AMD server on a Linux/Unix/HP-UX / FreeBSD / Solaris operating systems without rebooting the server or opening server case (cabinet)?

Most modern server supports 16GB, 32GB, 64GB or more RAM and has 4 or more DIMM slots. To find out what is the maximum system can support use any one of the following command as root user.