DATABEHANDLINGSANLEGGNING MED HUVUDMINNE OCH TABELLMINNE

The invention relates to memory-mapping and protection facilities in multi-processor data-handling systems. A feature of the invention relates to systems in which a plurality of processors, including both arithmetic processors and processors for the control of external data handling devices, communicate with each other and with a main store using a shared data-bus. Addresses generated by the processors are split into a most significant part A and a least significant part B. The part A is used to address a table store which generates the most significant digits P of the main store address, with an indication Q of the type of access permitted (e.g. read only or read and write). The digits P and B serve to form the address of a main store location or a device control processor function, the digits Q being communicated with them over the data-bus and used to address in a controlled manner, main store locations and device control processor functions. In the preferred implementation the table store holds a large number (e.g. 64) of tables and a table number store holds, for each processor the number of the table currently in use. This enables processors to be allocated tables rapidly and independently the table allocated being set to suit the task to be undertaken.