Parallel data processing apparatus

A controller operable to control an array of processing elements, the controller comprising:

• a retrieval unit operable to retrieve instruction items for each of a plurality of instructions streams, each instruction stream having a plurality of instructions items;
• a combining unit operable to combine the plurality of instruction streams into a serial instruction stream;
• a distribution unit operable to distribute the serial instruction stream to an array of processing elements;
• a plurality of instruction stream processors, one for each instruction stream, for controlling the respective instruction streams;
• a synchronization controller for controlling synchronization between instruction streams;
• a status block for providing status information regarding each of the instruction streams;
• and a scheduler connected to receive status information, and operable to determine which of the instruction streams is to be active.