Matrix multiplication is an example of application that is both easy to specify and to provide a simple implementation. There exist numerous sophisticated algorithms or very efficient complex implementations. In this study we are rather interested in the design/programming overhead with respect to performance benefits. Starting from the naive sequential implementation, the implementation is first optimised by improving data accesses, then by using vector units of modern processors, and we finally propose a parallel version for multi-core architectures. The various proposed optimisations are experimented on several architectures and the trade-off software complexity versus efficiency is evaluated using Halstead metrics.