1. A memory module storing data in the form of code words, each code word comprising useful bits and check bits for error correction, the memory module comprising: a first group of memory devices including check bits and a second group of memory devices including useful bits, the memory devices of the second group forming ranks, each rank being addressed as a whole, the ranks forming rank groups, each rank group including at least two ranks and a memory device from the first group; an interface; and a connecting device transferring bit packets each containing useful bits and check bits in the parallel format between the interface and the memory devices of a selected rank group.