Coattailing occurs when more than one piece of data is being transferred in or out of the host with a single channel input/output (I/O) operation. For example, without coattailing, each message read into VTAM® generates a READ channel program. A READ channel program uses CPU cycles. If you can read more than one message into VTAM and generate only one read channel program, then coattailing is taking place and you are saving CPU cycles. Coattailing can provide greater throughput between a host and an SNA controller because fewer interrupts and instructions are processed for each message. For further information, see Maximizing coattailing.