I/O Systemsin

OPERATING SYSTEM

Presented by

Shweta Patel

OBJECTIVES

•Understanding the various I/O devices and their characteristics.

•Understanding the role of device drivers.

•Understanding the transformation of I/O request to h/w operation.

VARIOUS I/O DEVICES

PURPOSE ACCESS MODE EXAMPLES

INPUT

Sequential Keyboard, Mouse

Random Disks

PRINT

Sequential Printers

Random Disks

STORAGE

Sequential Tapes, Disks

Random Disks

CHARACTERISTICS OF I/O DEVICES

DEVICE DRIVERS•Program in the operating system ,

responsible for managing the h/w device attached to the system.

•Insulates the applications from having to know the details about the physical connections , protocols and signals required to communicate with a device.

•The application doesn’t have to know the physical address of the port.

•In general, n applications can communicate with m devices using a common device driver.

•Employs a mapping table to communicate with a specific device.

•If the driver is using more than one device , then drivers can use resource table.

•To seek a device driver , system calls are used .

Device driver

Mapping table

Resource table

Channel

Device 1

Device 2

Device 3

Device Driver Implementation

TRANSFORMING I/O to H/W OPERATION

Ex. Reading a file from disk

•The application refers the file by the filename.

•A file system maps the file name to identify the space allocation for the file.

•The first part of the file (c:) identifies the specific h/w device.

STEPS

▫Determine device holding file. ▫Translate name to device representation.

▫Physically read data from disk into buffer.

▫Make data available to requesting application .

▫Return control to process.

LIFE CYCLE OF AN I/O REQUEST

TWO I/O METHODS

SYNCHRONOUS

ASYNCHRONOUS

THANK YOU !!