Kinds of Kernel-Level Drivers

• A character device driver transfers data as a stream of bytes of arbitrary length. A character device driver is called as a direct result of a user process issuing a system function call such as read() or ioctl().

• A block device driver transfers data in blocks of fixed size, and is called from the kernel to support filesystem or paging operations.

• A STREAMS driver is not a device driver, but rather can be dynamically installed to operate on the flow of data to and from any character device driver.