Abstract: A data storage apparatus uses a store having a nibble mode facility which allows two words to be accessed in a single extended cycle. Store access requests are held in a first-in-first-out queue in a buffer. When processing strings of data, double-read requests are alternated with pairs of write requests. A read request may be incorrectly aligned i.e. it may occur between a related pair of write requests. When an incorrectly aligned read request is detected, it is given priority so that it is executed ahead of its normal turn, and is then skipped when it is encountered during normal sequential read-out from the buffer. This allows the pair of write requests to be grouped together for execution in a single extended cycle.