Digital quantity is switch quantity, I is input switch quantity, O is output switch quantity, and IO digital quantity acquisition is the state of collecting input and output switch quantity.

Digital quantity is a kind of physical quantity.

The change of a physical quantity is discrete in time and quantity. Their changes are discontinuous in time and always occur in a series of discrete moments. At the same time, their values and each increase or decrease are integer multiples of a minimum unit of quantity, and values less than this minimum unit of quantity have no physical meaning. This kind of physical quantity is called digital quantity.

Digital quantity, that is, discrete quantity, refers to the dispersed quantity without intermediate value. For example, the value that a switch can take is discrete, and it can only be on or off, and there is no intermediate situation. But the value of the volume knob is continuous, and there are countless values between the maximum value and the minimum value. For example, 12% by volume, 13% by volume or 12.5% by volume.

Digital quantity (discrete quantity) corresponds to analog quantity (continuous quantity). The latter is very common in nature and can be analyzed by general mathematical methods. Digital information used for computer processing. Because the basic working state of computer is only 0 and 1, and the sampling of external information by digital computer system cannot be strictly continuous, and it must be completed only once in a cycle, so all digital quantities are processed in digital system. Moreover, digital quantity can not be completely analyzed by ordinary mathematical methods, and his analysis has special mathematical methods.