In a computer comprising multiple processing units, a method of exchanging read only elements between the processing units is described. The read only elements may be code or data, such as vector or matrix data for an AI graph. A master processing unit is identified. At compile time, at least one shareable read only element is allocated to the master processing unit. The at least one shareable read only element is stored in the local memory of the master processing unit. At compile time a transmitting exchange code sequence designated to be executed at the execution stage of the master processing unit is also allocated to the master processing unit. At a time point determined at compile time, the transmitting exchange code sequence causes the processing unit to identify the shareable read only element and to generate a message to be transmitted for reception by another processing unit, the message comprising the shareable read only data element.