<p>Registration times are assigned based on how many units you have completed. Therefore people with the earliest registration windows will have first chance at the classes they would like. As you progress through college you will be assigned a registration time that is earlier than your previous time slot. </p>
<p>Second point, many professors switch up their teaching schedule so they may or may not teach the same course in back to back quarters. In addition many professors don’t teach in back to back quarters at all and instead may teach fall and spring quarter taking winter quarter off for exclusive research time</p>