Question

why does a computer need two kinds of memory

Answer 1

to perform the computer fast.(without hang)and save to crupt the storage data save in computer memory.

Answer 2

Primary memory, like RAM, is required to run the processes which are ongoing during a particular time. For example, when you are playing a game, you are able to play the game smoothly at that particular time.

Secondary memory, like ROM or Hard Disk require to store the outcomes and results occured. For example, the game you completed this far is saved in Hard Disk which you can load again anytime.