Introduction of os and types

Introduction of OS
BY
Dr. V. S. PRAKASH
Assistant Professor
Department of Computer Science (UG)
Kristu Jayanti College

What is an Operating System?
• A program that acts as an intermediary between a user of a
computer and the computer hardware.
• It’s a program that control the execution of application program
• Acts as an interface between application and hardware
• Main Objectives of OS:
– Convenience, Efficiency, Ability to solve
• Operating system goals:
– Execute user programs and make solving user problems
easier.
– Make the computer system convenient to use.
• Use the computer hardware in an efficient manner.

Advantages of using Operating System
• Allows you to hide details of hardware by creating an
Easy to use with a GUI
• Offers an environment in which a user may execute programs/applications
• The operating system must make sure that the computer system convenient to use
• Operating System acts as an intermediary among applications and the hardware
components
• It provides the computer system resources with easy to use format
• Acts as an intermediate between all hardware's and software's of the system
• Disadvantages of using Operating System
• If any issue occurs in OS, you may lose all the contents which have been stored in
your system
• Operating system's software is quite expensive for small size organization which
adds burden on them. Example Windows
• It is never entirely secure as a threat can occur at any time

History of OS
• Operating systems were first developed in the late 1950s
to manage tape storage
• The General Motors Research Lab implemented the first
OS in the early 1950s for their IBM 701
• In the mid-1960s, operating systems started to use disks
• In the late 1960s, the first version of the Unix OS was
developed
• The first OS built by Microsoft was DOS. It was built in
1981 by purchasing the 86-DOS software from a Seattle
company
• The present-day popular OS Windows first came to
existence in 1985 when a GUI was created and paired with
MS-DOS.

Features of OS
• Protected and supervisor mode
• Allows disk access and file systems Device drivers
Networking Security
• Program Execution
• Memory management Virtual Memory Multitasking
• Handling I/O operations
• Manipulation of the file system
• Error Detection and handling
• Resource allocation
• Information and Resource Protection

What is a Kernel?
• The kernel is the central component of a computer
operating systems. The only job performed by the kernel
is to the manage the communication between the
software and the hardware.
• A Kernel is at the nucleus of a computer. It makes the
communication between the hardware and software
possible. While the Kernel is the innermost part of an
operating system, a shell is the outermost one.

Difference between the OS and Kernel
KERNEL
• Kernel is system software which
is part of operating system.
• kernel provides interface b/w
application and hardware.
• Its main purpose is memory
management, disk management,
process management and task
management.
• All operating system needs
kernel to run.
• Type of kernel includes
Monolithic and Micro kernel.
Operating System Concepts
OPERATING SYSTEM
• Operating System is a system
software.
• Operating System provides interface
b/w user and hardware.
• It also provides protection and
security.
• All system needs operating system to
run.
• Type of operating system includes
single and multi-user OS,
multiprocessor OS,real-time OS ,
Distributed OS.
• It is the first program to load when
computer boots up.

Computer System Components
1. Hardware – provides basic computing resources (CPU, memory,
I/O devices).
2. Operating system – controls and coordinates the use of the
hardware among the various application programs for the various
users.
3. Applications programs – define the ways in which the system
resources are used to solve the computing problems of the users
(compilers, database systems, video games, business
programs).
4. Users (people, machines, other computers).

Abstract View of System Components

Evaluation Of Operating System
•A Major OS evolve over time for no.
of reasons
– h/w upgrade
– New type of h/w
– New services provided

Operating System Definitions
• Resource allocator – manages and allocates resources.
• Control program – controls the execution of user programs and
operations of I/O devices .
• Kernel – the one program running at all times (all else being
application programs).

Simple Batch Systems
• Set of job with similar needs
– Eg: in our class we classify top level, meddle level and low level students
• In batch processing same type of jobs batch together & execute
at a time
• There is no direct interaction between user and computer.

Advantages OF BOS
• Sharing of batch system for multiple users.
• The idle time batch system is very less.
• You can assign specific time for the batch jobs so when the
computer is idle it starts processing the batch jobs i.e. at
night or any free time.
• The batch systems can manage large repeated work easily.

Disadvantages OF BOS
•Computer operators must be trained for using
batch systems.
• It is difficult to debug batch systems.
• Batch systems are sometime costly.
•no direct interaction between user and computer
• If some job takes too much time i.e. if error
occurs in job then other jobs will wait for
unknown time.
•No mechanism to prioritize processes.
•CPU is often idle, because the speeds of the
mechanical I/O devices is slower than CPU.

Examples of BOS
1.Payroll system
• Batch systems are ideal for making payrolls. The salaries
of employees can be printed at the end of month by the
batch systems. So the statements can be made easy by
using batch systems.
2.Bank statements
• At the end of month the bank makes statements for each
account holder. So these bank statements can be made
easily by batch systems at the end of month.

Multiprogrammed Batch Systems
Several jobs are kept in main memory at the same time, and the
CPU is multiplexed among them.

Multiprogrammed Batch Systems
•In this the operating system, picks and
begins to execute one job from memory.
•Multiprogramming system, CPU will never
be idle and keeps on processing.

• ADVANTAGES
• It increases CPU utilization.
• It maximizes the total job throughput of a
computer.
• Better Reliability-if one processor breakdown
then other takes its workload.
• DISADVANTAGES
• It must keep track of all kinds of jobs.
• Each system requires large chunks of hard drive
space which cannot be allocated to programs
• Poor CPU usage when only one program is
present in memory.

OS Features Needed for Multiprogramming
• I/O routine supplied by the system.
• Memory management – the system must allocate the memory to
several jobs.
• CPU scheduling – the system must choose among several jobs
ready to run.
• Allocation of devices.

Time-Sharing Systems–Interactive Computing
• It is similar to Multi programming system.
• It can be used to handle multiple interactive job.
• Processor time is shared among the multiple users.
• The CPU is multiplexed among several jobs that are kept in
memory and on disk (the CPU is allocated to a job only if the job
is in memory).
• A job is swapped in and out of memory to the disk.
• On-line communication between the user and the system is
provided; when the operating system finishes the execution of
one command, it seeks the next “control statement” not from a
card reader, but rather from the user’s keyboard.
• On-line system must be available for users to access data and
code.

Time-sharing systems
User 5 is in active state-has CPU time
User 6 is in the ready queue
User 1,2,3, are in the waiting state (wait
queue)
Advantages:
1. Many users tasks are processed
simultaneously
2. Cpu idle time is minimized
3. Less response time
4. Resources are shared
Disadvantage:
1.Requires memory mgmt
2. CPU scheduling algorithms
3. Disk management and protection
mgmt
4.May stuck in deadlock.

Personal-Computer Systems
• Personal computers – computer system dedicated to a single
user.
• I/O devices – keyboards, mice, display screens, small printers.
• User convenience and responsiveness.
• Can adopt technology developed for larger operating system’
often individuals have sole use of computer and do not need
advanced CPU utilization of protection features.

Migration of Operating-System Concepts and Features

Parallel Systems
• Multiprocessor systems with more than one CPU in close
communication.
• Tightly coupled system – processors share memory and a clock;
communication usually takes place through the shared memory.
• Advantages of parallel system:
– Increased throughput
– Economical
– Increased reliability

Parallel Systems (Cont.)
• Symmetric multiprocessing (SMP)
– Each processor runs an identical copy of the operating
system.
– Many processes can run at once without performance
deterioration.
– Most modern operating systems support SMP
• Asymmetric multiprocessing
– Each processor is assigned a specific task; master
processor schedules and allocates work to slave processors.
– More common in extremely large systems

Symmetric Multiprocessing Architecture

Real-Time Systems
• Often used as a control device in a dedicated application such as
controlling scientific experiments, medical imaging systems,
Traffic system, industrial control systems, and some display
systems.
• Well-defined fixed-time constraints.
• Hard real-time system( purly Deterministic system and time
constrain sys)).
– Secondary storage limited or absent, data stored in short-
term memory, or read-only memory (ROM)
– Conflicts with time-sharing systems, not supported by
general-purpose operating systems.
 Eg: Satelite system
• Soft real-time system
– Limited utility in industrial control or robotics
– Useful in applications (multimedia, virtual reality) requiring
advanced operating-system features.
– System meeting deadline is not compulsory
– Eg: Personal computer , audio & video system

Distributed Systems
• Distribute the computation among several physical processors.
• Loosely coupled system – each processor has its own local
memory; processors communicate with one another through
various communications lines, such as high-speed buses or
telephone lines.
• Advantages of distributed systems.
– Resources Sharing
– Computation speed up – load sharing
– Reliability
– Communications

Distributed Systems (Cont.)
• Network Operating System
– provides file sharing
– provides communication scheme
– runs independently from other computers on the network
• Distributed Operating System
– less autonomy between computers
– gives the impression there is a single operating system
controlling the network.

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Introduction of os and types

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