We have developed a modular toolkit for hands-on experimentation which enables students to build and test a wide variety of computer architectures. This toolkit is based on a decomposition into three hierarchical layers: a layer of the CPU's internal modules (e.g. an ALU), a layer of internal processor modules (e.g. a cache module), and one of processor modules (e.g. a 68000 motherboard). This toolkit allows experimentation on a complex multiprocessor array as easily as experimentation on a simple pedagogical computer, with the same user interface and minimal changes in the environment. The toolkit has been designed to be driven either locally, through a pedagogical and powerful front panel, or through a remote host (such as any workstation supporting X Window and Motif, or a Macintosh).