Designing a modern processor is a very complex task. Writing the entire design using a hardware description language (like Verilog) is time consuming and difficult to verify. There exists a split architecture/microarchitecture description technique, in which, the description of any hardware can be divided into two orthogonal descriptions: (a) an architectural contract between the user and the implementation, and (b) a microarchitecture which describes the implementation of the architecture. The main aim of this thesis is to build realistic processors using this technique. We have designed an in-order and an out-of-order superscalar processor using the split-description compiler. The backend of this compiler is another contribution of this thesis. / text