Question

4gb ram game can start in 1gb ram laptop

Answer 1

it will start but while playing it will lag very much.

Answer 2

Running a 4GB program on a computer having a RAM of 1GB.

    There is a method called overlays. There is a swap space on the disk. It is used by the operating system to move unneeded contents of memory in there. For example some other processes or programs related to other users could be moved over there. When they are required again, they could be loaded back.

    So the big game could be loaded chunk by chunk and could be executed by the OS on the computer.  So during the execution of the program it is possible that the execution stops temporarily for loading the parts of the game into the disk , to the swap space and from swap space into memory.

    The game runs slow. However, it could run.