1. A method for operating a memory in turbo decoder, comprising calculating forward metrics of received data during a first window; storing forward metrics calculated during said first window in said memory; calculating forward metrics of received data during a second window; and storing the forward metrics calculated during said second window in said memory wherein each forward metric to be stored in said memory and calculated during said second window is read into a memory location in said memory which is occupied by a forward metric calculated during said first window and which is being read out of the memory for use in a reverse metrics calculation.