A character device driver that implements the STREAMS interface. A STREAMS device driver exists below the Stream head and any modules. It can act on an external I/O device, or it can be an internal software driver, called a pseudo-device driver. The driver transfers data between the kernel and the device. The interfaces between the driver and kernel are known collectively as the Solaris 7 Device Driver Interface/Driver Kernel Interface (Solaris 7 DDI/DKI). The relationship between the driver and the rest of the UNIX kernel is explained in Writing Device Drivers. Details of device drivers are explained in Chapter 9, STREAMS Drivers.