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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
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 !!