1. A computer processing system, said processing system comprising: a first memory for storing programs and data associated with said programs; a plurality of first processing units for processing said programs and said associated data; a memory controller for controlling accesses to said first memory by said first processing units; a second memory for storing an access table and a key table, said access table comprising a plurality of access entries, each said access entry including an access key and an identification of a memory space within said first memory associated with said access key, said key table comprising a plurality of key entries, each said key entry including an identification of one of said first processing units and a request key associated with said first processing unit; a second processing unit for controlling said processing of said programs and said associated data by said first processing units, said second processing unit being operable to construct and maintain said access table and said key table, said second processing unit being further operable to direct any one of said first processing units to process one of said programs, said one first processing unit being operable in processing said one program to issue a request to said memory controller for access to a storage location within said first memory, said memory controller being operable, in response to said request, to compare the request key associated with said one processing unit in said key table with the access keys in said access table, and if one of said access keys corresponds with the request key associated with said one first processing unit in said key table and said storage location corresponds to the memory space associated with said one access key identified in said access table, to execute said request.