1. A decoder for decoding forward error correcting codewords using a parity check matrix comprising a plurality of sub-matrices, the decoder comprising: a plurality of check node processing units to receive a forward error correction codeword, each check node processing performing, in parallel, a check node computation corresponding to a different row of the parity check matrix to generate a plurality of check node output messages; and a plurality of variable node processing units, each variable node processing unit to receive the plurality of check node output messages and to perform a variable node update computations corresponding to different columns belonging to a same sub-matrix of the parity check matrix to generate variable node output messages; and an output circuit to generate a decoded codeword based on the variable node output messages.