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<p>It depends on which classes. The usual large classes are popular ones like introductory economics, psychology, chemistry, and biology, as well as common requirements for many majors like math. However, introductory computer science courses have lately gotten much more popular, with fall term enrollments over 1,000 at Berkeley and over 700 at Stanford and Harvard (the latter two are especially impressive in a relative sense, since the fall term enrollment in introductory computer science is nearly half of their frosh classes).</p>