4cf306ce_a_620___Phone_specs_comparison__Hardware
[1] 256 MB RAM / 1024 MB ROM [2] 512 MB RAM [Hardware] 
System memory System memory - System memory, or RAM memory is the type of memory that the device uses to temporarily store data from the OS or currently-running apps. The more RAM available to the device, the better the performance will be when multiple or heavier programs are running.
Nokia X7 vs Nokia Lumia 620 - Phone specs comparison