Also, for 100B, I think it has something to do with there being a letter after the name. Without checking, I'm willing to guess that there are other courses at MIT numbered X.100 but not any numbered X.100B.
But on the first day of 18.100B, I distinctly remember the professor saying: "some of you are freshmen. this course is too hard for freshmen. it's also too hard for sophomores, juniors, seniors, and maybe some grad students."
Also, for 100B, I think it has something to do with there being a letter after the name. Without checking, I'm willing to guess that there are other courses at MIT numbered X.100 but not any numbered X.100B.
But on the first day of 18.100B, I distinctly remember the professor saying: "some of you are freshmen. this course is too hard for freshmen. it's also too hard for sophomores, juniors, seniors, and maybe some grad students."