Long description

The figure consists of a block labeled layer which is divided into five segments. The five segments are labeled from top to bottom as follows. User processes, Device-independent software, Device drivers, Interrupt handlers, and Hardware. Three arrows pointed downward starting from the first layer to the last layer sequentially are labeled I O request and another four arrows pointed upward from bottom to top layer are labeled I O reply.

The I O functions of each layer from top to bottom are labeled as follows. Layer 1: Make I O call; format I O; spooling. Layer 2: Naming, protection, blocking, buffering, allocation. Layer 3: Set up device registers; check status. Layer 4: Wake up the driver when I O completed. Layer 5: Perform I O operation.