This document discusses input/output (I/O) systems in operating systems. It describes various I/O devices like keyboards, mice, printers and disks and their characteristics. It explains that device drivers manage hardware devices and insulate applications from needing to know details of physical connections. The document outlines how an I/O request is transformed into a hardware operation like reading a file from disk by mapping the file name to the storage space and physically reading the data.

1. I/O Systems
in
OPERATING SYSTEM
Presented by
Shweta
Patel

2. 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.

3. 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

4. CHARACTERISTICS OF I/O DEVICES

5. 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.

6. • 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 .

7. Device driver
Mapping table
Resource table
Channel
Device
1
Device
2
Device
3
Device Driver Implementation

8. 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.

9. 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.

10. LIFE CYCLE OF AN I/O REQUEST

11. TWO I/O METHODS
SYNCHRONOUS ASYNCHRONOUS