This document discusses asynchronous data transfer between a CPU and I/O device. It describes two common methods - strobe control and handshaking. Strobe control uses a single control signal to indicate when valid data is available on the data bus. This can be source-initiated, where the source activates the strobe, or destination-initiated, where the destination activates the strobe to request data. Handshaking accompanies each data transfer with control signals from both the sender and receiver to acknowledge the data.