This document discusses system calls, inter-process communication models, system programs in operating systems, and virtual machines. It describes how system calls provide an interface for processes to request services from the operating system, including process control, file management, device management, and communication. It explains the shared memory and message passing models for inter-process communication. It outlines different types of system programs for file management, status information, file modification, programming language support, program loading and execution, and communications. Finally, it describes how virtual machines allow multiple operating systems to run concurrently and isolated on the same physical computer.

2. System Calls
 System calls provide an interface to the services made available by
an operating system.
 Type of system calls:
 Process control (e.g., create and destroy processes)
 File management (e.g., open and close files)
 Device management (e.g., read and write operations)
 lnformation maintenance (e.g., get time or date)
 Communication (e.g., send and receive messages)

3. System Call Flow

4. System Calls

5. Communication Models
• if a process cannot affect or be affected by the other processes
executing in the system then the process is said to be
independent.
• So any process that does not share any data with any other
process is independent.
• A process is said to be cooperating if it can affect or be affected
by the other processes executing in the system.
• So it is clear that, any process which shares its data with other
processes is a cooperating process.

6. • Cooperating processes need an inter-process communication
(IPC) mechanism that will allow them to exchange data and
information.
• Two basic models of inter-process communication are there:
shared memory and message passing.

7. • A region of memory that is shared by cooperating processes is
established, in shared-memory model.
• Processes can then exchange their information by reading and
writing data to the shared region.
• In message-passing model, communication takes place by
means of messages exchanged between the cooperating
processes.

8. Communication Models

9. System Programs in Operating
System
• System Programming can be defined as the act of building
Systems Software using System Programming Languages.
• System Programs can be divided into these categories :
• File Management
• Status Information
• File Modification
• Programming-Language support
• Program Loading and Execution
• Communications

10. • File Management –
• A file is a collection of specific information stored in the memory
of a computer system.
• File management is defined as the process of manipulating
files in the computer system, its management includes the
process of creating, modifying and deleting files.

11. • Status Information –
Information like date, time amount of available memory, or disk
space is asked by some users.
• Others providing detailed performance, logging, and debugging
information which is more complex.
• All this information is formatted and displayed on output devices
or printed.
• Terminal or other output devices or files or a window of GUI is
used for showing the output of programs.

12. • File Modification –
For modifying the contents of files we use this.
• For Files stored on disks or other storage devices, we used
different types of editors.
• For searching contents of files or perform transformations of
files we use special commands.

13. • Programming-Language support –
For common programming languages, we use Compilers,
Assemblers, Debuggers, and interpreters which are already
provided to users.
• It provides all support to users. We can run any programming
language.

14. • Program Loading and Execution –
When the program is ready after Assembling and compilation, it must
be loaded into memory for execution.
• A loader is part of an operating system that is responsible for loading
programs and libraries. It is one of the essential stages for starting a
program.
• Communications –
Virtual connections among processes, users, and computer systems
are provided by programs.
• Users can send messages to another user on their screen, User can
send e-mail, browsing on web pages, remote login, the
transformation of files from one user to another.

15. Virtual Machines
• A virtual machine is an execution of computer system within our
physical personal computer.
• A virtual machine allows users to install and run multiple operating
systems in a single PC thereby making an illusion that each separate
execution environment is running its own private computer.
• Here resources of computer system are shared to each OS running by
virtual machine.

17. Advantages
• Virtual machines provide higher degree of protection to various
resources of the system because if any of the OS corrupted or
malfunctioned leads to affect only that relevant virtual machine
• Other users of virtual machine can continue their routine operations
without being disturbed.
• Various OS can be run concurrently to serve the different needs of
various users
• Multiple OS environment can exists simultaneously on the same
machine isolated from each other
• Easy maintenance, availability and convenient recovery.

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