The invention concerns a method for dynamically allocating memory workspace of an onboard system to a data structure identified by an identification number (ID_A_k) and the corresponding onboard system. The storage area of the onboard system being subdivided into elementary memory blocks (BL₁), the method is implemented on the basis of an allocation instruction and an erasure instruction. To allocate (A) an elementary memory block, the method consists in assigning an identification number (ID-A_k) to the block concerned. To erase (E) an elementary storage block, the method consists in assigning an arbitrary value (AAAA) different from any identification number. The system is applicable to onboard systems, such as multi-application microprocessor cards.