with the most-used letters on the center (home) row, so that you don’t have to move your fingers up and down as much. the home row is AOEUIDHTNS the lesser used letters PYFGCRL are in the row above, and the even lesser used letters QJKXBMWVZ are below.
I’m an excellent typist and can type well on both keyboards though occassionally when I use a letter that is the same position on both keyboards, such as A, I will occasionally switch keyboard modes and start typing as if I were on the other keyboard.
In english, the most commonly used letters are ETAIONSHRDLU – see how much wasted movement there is on a QWERTY keyboard.