Linear A levels mean that all exams will be taken at the end of the two years and these are the only things that will influence your final grade. This essentially makes AS level exams redundant (unless you plan on dropping the course), which is why most schools have stopped running them and universities have stopped making them a requirement. Modular courses, on the other hand, are made up of several sections/modules which are taken over the course of the two years. For these courses, your AS exams will form part of your final grade along with your A2 exams and any coursework that is required as well.