Abstract: A data compressor has a delta value calculator which receives data items and determines if a related data item to a received data item is stored in a data store. If the related item is stored, the delta value calculator retrieves the related data item from the data store and calculates a delta value from the received data item and the related data item. If the related item is not stored, then the delta value is calculated from the received data item and a predetermined value. A data store controller accesses the data store in response to receipt of a data item and determines if a storage location is allocated to the data item. If there is an allocated storage location for the data item, the data item is stored in the allocated storage location; and if not then a storage location is allocated to the data item.

Abstract: A data compressor is disclosed for receiving a data stream comprising a plurality of data items and for outputting a compressed data stream, said data compressor comprising: a data input for receiving said data stream; a delta value calculator for generating a compressed delta value, said delta value calculator being configured to receive said plurality of data items from said data input and being configured for at least some of said received data items to access said data store to determine if a related data item to said received data item is stored in said data store and: in response to said related data item being stored, to retrieve said related data item from said data store and to calculate a delta value from said received data item and said related data item and to output said delta value; and in response to said related data item not being stored in said data store to calculate a delta value from said received data item and a predetermined value and to output said delta value; a data store for storing