Linux will let you allocate as much memory as you want. It doesn't ever return failure based on available memory. Instead if you attempt to write to memory it

Linux will let you allocate as much memory as you want. It doesn't ever return failure based on available memory. Instead if you attempt to write to memory it will then map memory and if there is none available it will trigger the OOM killer. The kernel will attempt to kill misbehaving processes. The 4GB limit is maximum memory that can be allocated to a process (this is configurable) http://en.wikipedia.org/wiki/OOM_Killer http://en.wikipedia.org/wiki/OOM_Killer