V22.0436 - Prof. Grishman

Lecture 26: Input-Output: DMA

Text: Chapter 8

Control and Status Registers

Each I/O device is connected to the I/O bus through a controller. A simple controller will have at least 3 addresses (ports) on the bus, each corresponding to a register in the controller More complex devices (e.g., disks) will have multple control and status registers.

Direct Memory Access

(text, pp. 571-573)

Intelligent device controllers

Since simple processors are so cheap, it makes sense to place more intelligence in the device controller by using a processor with a fixed (ROM) program to handle the low-level IO management, such as the transfer of multiple sectors from a disk, or handling the protocol for a communication line (error checking, etc.)