I know that preliminary exams/comps/whateveryoucall it differs by program and specialization, so I always find it interesting to hear other's experiences.
I'll be taking my prelims soon and my format is two days (one day each for my areas of interest) written and one day of oral. My written will be (each) 6 hours long to answer 3 out of 4 questions (no notes). The oral reviews your written, as well as anything else your committee wants to ask you.
How does your program do prelims?