A computer, including a plurality of processing nodes arranged in two-dimensional arrays in respective front and rear layers. Each processing node has a set of activatable links. When activated, transmission of data items between the nodes connected via the activated link is enabled. When not activated, transmission of data items between the nodes is prevented. The set of activatable links including a respective link which connects the processing node to each adjacent node in the array, and to a facing processing node in the other layer. An allocation engine is configured to receive an allocation instruction and connected to the processing nodes to selectively activate the links in a configuration.