G22.2233 - Prof. Grishman

Lecture 13: Input-Output: Busses and Control of Transfer

Bus performance

Trade-off between cost, capacity, and speed (fig. 8.14, page 671):

Controlling input-output transfers

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 multiple control and status registers.

Direct Memory Access

(text, pp. 680-682)

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.)

Spring 2002