I/O is an abbreviation of Input / Output and refers to the transfer of data to or from an application.
Input devices are usually but not always character input devices such as the keyboard, mouse or keyboard. They can also include stream devices like a disk. Output devices include the screen or a printer or anything plugged into a PC's port.
The simplicity of flat cable design, with its parallel conductor geometry, eliminates many of the common sources of wiring error and malfunction. Registration of the conductors is one-to-one with the terminating connector or board so that proper contact assignment is almost automatic. Flat cables also fold and bend readily, conforming to the mounting area, and they fasten easily with clamps, adhesive, or double-faced tape. Since the conductors are visible and in a fixed position within the dielectric coding, inspection and circuit tracing are simplified.  Hence, the conductor spacing is fixed and the geometry of the cable is constant, the electrical characteristics such as impedance, capacitance, inductance, time delay, crosstalk and attenuation are consistent.