A method and an apparatus for creating a data block (Error Correction Code Block) comprising a plurality of data sectors, which data block is provided with parity information, and a method and an apparatus for recovering data sectors from a data block provided with parity information. A method for encoding or decoding data streams, respectively, which has a reduced memory requirement and manages with two encoders or decoders, respectively, and an encoding or decoding unit, respectively, for implementing the method, are proposed. In the case of a method for creating an ECC block comprising a plurality of data sectors, the data sectors being buffer-stored in the form of a block with a plurality of rows in a memory organized in the form of rows and columns and being provided with parity information, successively received blocks of data sectors are written row by row alternately to the rows or columns, respectively, of the memory.