This invention relates to memory cards. Microprocessor cards generally use application programmes contained in a non-volatile user memory (MU) controlled by an operating system in the read-only memory (MSYS). In order to provide flexibility and to ensure protected access to the different storage areas, without using any specific set circuitry, it is proposed that the storage access instructions of the application programmes (PG1, PG2, PG3) should be interpreted but not directly executed; the interpreter is contained in the read-only memory (MSYS) or in the user memory, and executes an access instruction in the following way: an allocated area (ZR) of the user memory is explored to determine if the requested access (read, write, execution) is authorized for the requested address; the instruction is only executed if such an access authorization is present. The allocated area (ZR), which contains such access authorizations is updated when a new application programme is written into the user memory. Updating can only be implemented by the operating system.