Examples of techniques for processing I/O operations in a channel are disclosed. In one example implementation according to aspects of the present disclosure, a computer-implemented method may include: copying, by a system assist processor, a subchannel of the channel into a lower portion of a channel communication area responsive to receiving the I/O operation; copying, by the system assist processor, channel program information from a designated starting location in a customer memory into a control block; building, by the system assist processor, a starting channel communication area into a top portion of the control block; queuing, by the system assist processor, the control block to a queue for the channel; processing, by the channel, the I/O operation responsive to retrieving the control block from the queue.