why do the key board keys f and j have bumps on them?

Answer 1

So you can find them without looking. They are in the "home" row of the keyboard and they are where your index fingers should rest before you begin typing.

Answer 2

These are the "home" keys for touch typing. The pips identify them without you having to look at the keys.

Answer 3

so you know where to put your fingers at. your left and right fingers start on those keys. so it kind of gets you set on the keyboard with out looking at it. I use it all the time.

Answer 4

because the most common configuration of the keyboard is qwerty that means the order of the first five letters, the bumps in the f and j is for people to know where the center letters are so you don't have to see the keyboard while typing.

http://en.wikipedia.org/wiki/QWERTY