This chapter describes how Real Time-Thread (RT-Thread) manages different input/output (I/O) devices. RT-Thread is divided into three layers. From top to bottom are the I/O device management layer, device driver framework layer, and device driver layer. The device driver framework layer is an abstraction of the same kind of hardware device drivers. The same characteristic of its kind is extracted, and the unique characteristics are left out of interface, which should be implemented by the driver. The device model in RT-Thread is based on the kernel object model, which is considered a kind of object and is included in the scope of the object manager. Character devices and block devices are used device types, and their classification is based on the transmission processing between device data and the system. Character mode devices allow for unstructured data transfers, that is, data usually transfers in the form of serial mode, one byte at a time.