This presentation discusses system calls and provides an overview of their key aspects: System calls provide an interface between processes and the operating system. They allow programs to request services from the OS like reading/writing files. There are different methods of passing parameters to the OS, such as via registers, parameter blocks, or pushing to the stack. System calls fall into categories including process control, file management, device management, information maintenance, and communication. An example is given of how system calls would be used in a program to copy data between two files.

1. Presentation On:
SYSTEM CALLS
Reference Book :
Operating System Organisation With Special
Reference To UNIX
By Satyapriya Bhattacharjee
Presented by;
Bernard Senam Parkoo
MSc. II, DOS In Computer Science

2. Presentation Outline
• What are System Calls
• Scenario of System Calls
• How a System Call Occurs
• Methods of Passing Parameters to the OS
• Categories of System Calls

3. What are System Calls
• System Calls provide the Interface between a
process and the Operating System.
• These calls are generally available as Assembly
language instruction.
• System Calls can also be made directly through
HLL programs for certain systems.
• UNIX System calls can be invoked directly from a
C or C++ program.

4. Scenario of System Calls
An Example of how system calls are used.
• Consider a simple program to copy data from one
file to another file .
• The first input of the program will be the name of
both files.
• These names can be specified depending on the
design of Operation System
• Once the file names are obtained, the program
opens an input file and create an output file
• Each of this operations require other System calls
and may encounter possible error conditions.

5. How System Calls Occur.
System Calls occur in different ways depending on the
computer in use:
• More information is required than just the identify of the
desired System call.
• The exact type and amount of information varies
according to the operation system and call
• For instance to get an input we need to specify the file of
device to use as source and the address and length of
memory buffer into which the input should be read.

6. Methods of Passing Parameters to
Operating System
Three methods are used in passing parameters to the
operation system.
• The simplest is approach is to pass parameter
through registers.
• The second is by storing parameters in blocks and
passing the address through registers.
• Finally parameter can be pushed into stack by the
program and popped of by the Operating System.

7. Categories of System Calls
System calls can be grouped into five major
categories as follows.
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Process control
File management.
Device management
Information Maintenance and
Communication.

8. Process control
Some system calls under process control are:
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End, abort
Load, execute
Create process, terminate process
Get process, terminate process
Wait for time
Allocate and free memory

9. File management.
Some system calls under file management are:
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Create file, delete file
Open , close
Read, write, reposition.
Get file attributes, set fil attributes

10. Device management
Some system calls under device management are:
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Request Device, release device
Read, write, reposition.
Get device attributes and set device attributes
Logically attach or detach devices

11. Information Maintenance
Some system calls under information maintenance
are:
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Get time or date, Set time of date
Logically attach or detach devices
Information maintenance
Get system data, Set Systems data
Get process, file of device attributes
Set process, file or device attributes

12. Communication
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Create, delete communication connection.
Send, receive messages
Transfer status information
Attach or detach remote devices.

13. The End