This invention concerns an optimised management method for allocating memory space of an onboard system to a data structure and a corresponding onboard system. The object code packets and the data packets being discriminated, and the memory being subdivided into addressable elementary memory blocks, the method consists in allocating (A.sub.1) to the object code packets a set of elementary memory blocks located in a first memory space (MS.sub.1) to addresses substantially adjacent and to the data packets another set of elementary memory blocks located in a second memory range (MS.sub.2). This enables to avoid fragmentation of the memory zone, during successive installations/deinstallations and to implement very easily an optimal defragmentation procedure, adapted to each type of data, code or application data.