The Proceedings of the 6th Brazilian Workshop on High Performance Computing Systems (WSCAD 2005) bring the papers selected and presented in the edition of the event held in Rio de Janeiro/RJ, from October 24 to 27, 2005. In this issue, the proceedings include 24 full papers. These papers were selected through a peer-review, from a total of 88 full papers submitted, which implied an acceptance rate of 27,3%. The event's program committee was coordinated by Maria Clicia Stelling de Castro (UERJ) and Edson Midorikawa (USP), who organized this volume.