Abstract: A memory module selection and reconfiguration apparatus in a data processing system wherein a modular working memory formed by a plurality of memory modules sends to a central processing unit information related to the capacities of the constituting modules (M1, M2, M3, M4) during the system initialization. The central unit processes such information and provides memory, via a channel (30), with information representative of the capacity of the first modules (G1), of the sum of the capacities of the first and second module (G2), of the sum of the capacities of the first, second and third module (G3) and so on, up to the total capacity of the working memory. This information is stored into registers (31, 32), each one related to a possible module, of a module selection unit included inside the working memory.