Our brain’s working memory like a computer’s RAM is of limited capacity.

Though there is still dispute on maximum number of items that can be kept in working memory at one time , the number 4 is the mostly accepted number.

This being said a lot of the great personalities can efficiently multi task for top performance.

How this is done is through rigorous practice , to convert mundane work into routines that become habit patterns in the basal ganglia.

Habits do not occupy the conscious mind and can operative out of our subconscious mind , thus enabling efficient multi tasking by tricking the brain.