From Linuxintro

Computer RAM (random access memory) holds the data for the CPU, typically loaded from hard disks or read from keyboard.

Find out your memory configuration

To find out how much RAM you have, enter

# hwinfo --memory
01: None 00.0: 10102 Main Memory
  [Created at memory.59]
  Unique ID: rdCR.CxwsZFjVASF
  Hardware Class: memory
  Model: "Main Memory"
  Memory Range: 0x00000000-0xc7fffffff (rw)
  Memory Size: 50 GB
  Config Status: cfg=new, avail=yes, need=no, active=unknown

In this case you have 50 GB of memory.

To find out what dimms you have, use

# dmidecode | less
Memory Device
        Array Handle: 0x1000
        Error Information Handle: Not Provided
        Total Width: 72 bits
        Data Width: 64 bits
        Size: 4096 MB
        Form Factor: DIMM