Linux is much better at multitasking processor-intensive tasks than Windows. I remember how virus scanning used to make by old Windows PC almost unusable. Linux is much better, but occasionally you may need to pause a process that is slowing things down.
Open a terminal. Run ps or ps aux to find the PID of the process you want to stop. If you want a program to try this out with, open xeyes with xeyes& on the terminal. (The ‘&’ symbol launches the program in the background.) This will create a window with eyes that follow your cursor around, you will be able to tell that it is paused when the eyes stop moving.
Now run kill -STOP 7727 but replace the number with your own xeyes PID. The eyes will stop moving when they are paused.
To continue execution of xeyes, run kill -CONT 7727, again with your own PID. The eyes will start moving again.
When you are done you can end xeyes with kill 7727 (using your own PID).
Now you can pause and resume any application you like. Thanks to A Linux SysAd Blog for explaining this.