A data handling system for transferring data between two units, the data being transferred in blocks of a selected number of data words, up to predetermined maximum number. A buffer stores the data being transferred. The buffer includes a plurality of stages (70, 71, 72, 73) arranged serially from an input end (70) to an output end (73), the number of stages being equal in number to the predetermined maximum number of data words that may be transferred in a block. If the number of data words being transferred is less than the predetermined maximum number, as indicated by a control signal (S0, S1) from the unit transmitting the data, the buffer either receives the data in the stage a number of stages from the output end, or transmits the data from the stage a number of stages from the input end, equal to the number of words being transferred in the block.