A subsystem is the circuitry (ADCs, DACs, clocks, triggers, timing signals, timing engines, and so on) that a device uses to acquire or generate samples. On DAQ devices, there are separate subsystems for analog input, analog output, each counter, and digital I/O. A subsystem is not synonymous with I/O type, however. For instance, each counter's input and output circuitry make up one subsystem. The trigger bus can also function as a subsystem.