Students can demonstrate breath of knowledge in computer science by passing written qualifying exams. The exams are offered once every semester (usually two weeks before the semester begins).
To qualify, each student must pass exams in four areas, one of which is Foundations of Computer Science. The other three areas are chosen from these eight areas: computer systems; networks; compilers and languages; software construction; software testing; artificial intelligence; database systems; and information security.
The four exams must be attempted in the same semester, and a failed exam may be retaken once only, in the next semester. A student who fails to pass the four exams in two consecutive semesters is subject to dismissal from the program.
See this web page for the current policies and procedures for taking the CS PhD qualifying exams.