The world's first computer science degree program started at Cambridge in 1953. The course today continues to enjoy a fantastic reputation academically and in industry.
You cannot study only computer science in your first year. It must be combined with maths and either a natural science subject, psychology or more mathematics.The Computer Lab website gives details of the course contents and modules: http://www.cl.cam.ac.uk/admissions/undergraduate/. The course is a lot more mathematical than most applicants expect, and actually writing code requires only a small percentage of time compared to the rest of the course.
In my first year, I had 12 hours of lectures per week, divide equally between each of the two computer science papers, maths and physics. I then had three supervisions each week in computer science, physics and maths. There were also three practical sessions per fortnight, lasting approximately three hours each. For each of my three supervisions, I had about six hours of work to do.
At Peterhouse, there will be very few people studying computer science. In recent history, there has been zero or one computer scientist per year. Peterhouse does not have a computer science fellow and so your director of studies, and all your computer science supervisions, will be at Trinity. The lack of peers studying computer science in Peterhouse makes it difficult to get help. However, being the only computer scientist in the year is great fun and allows you mix with a whole host of people doing other subjects but also forces you to make friends with computer scientists outside your college.
If you are looking to apply, make sure your personal statement demonstrates that you understand what the course is about and how mathematical it is, and why that appeals to you. Before interview, prepare by brushing up on your maths. If you are looking for more computer science topics to investigate, try reading The New Turing Omnibus or The Pleasures of Counting.
If you are coming to Peterhouse to study computer science, massive congratulations! Many people make friends who do the same subject but at Peterhouse that resource is somewhat limited! It is therefore important that you take part in as many freshers' week events as you can and get to know as many people as possible. You should also get talking to as many different people as possible in lectures too. Computer scientists have a reputation for being reserved, but getting to know others who do your subject will be will worth the little effort that it requires.
Computer science is a fantastic subject to study and there is no better place to study it than at the Cambridge Computer Lab.
George Thomas, 2013