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+.. include:: <isonum.txt>
+
+============
+Introduction
+============
+
+The main purpose of the Industrial I/O subsystem (IIO) is to provide support
+for devices that in some sense perform either
+analog-to-digital conversion (ADC) or digital-to-analog conversion (DAC)
+or both. The aim is to fill the gap between the somewhat similar hwmon and
+:doc:`input <../input>` subsystems. Hwmon is directed at low sample rate
+sensors used to monitor and control the system itself, like fan speed control
+or temperature measurement. :doc:`Input <../input>` is, as its name suggests,
+focused on human interaction input devices (keyboard, mouse, touchscreen).
+In some cases there is considerable overlap between these and IIO.
+
+Devices that fall into this category include:
+
+* analog to digital converters (ADCs)
+* accelerometers
+* capacitance to digital converters (CDCs)
+* digital to analog converters (DACs)
+* gyroscopes
+* inertial measurement units (IMUs)
+* color and light sensors
+* magnetometers
+* pressure sensors
+* proximity sensors
+* temperature sensors
+
+Usually these sensors are connected via :doc:`SPI <../spi>` or
+:doc:`I2C <../i2c>`. A common use case of the sensors devices is to have
+combined functionality (e.g. light plus proximity sensor).