Kohina said..
Sometimes people will need more memory than what the RAM installed can offer during intensive application cycles. During these sessions, the computer will conduct a task known as swapping.This is when the computer temporarily uses the hard drive space in place of the memory. Thrashing is the term for constantly swapping, but as the name's
connotation suggest, constant thrashing can decrease the overall system performance. More RAM being added can reduce the swapping rate.