Explain About Computer Operating System

 Explain About Computer Operating System

What is computer operating system?

An operating system is a system software that provide a virtual machine that hides hardware details, provides I=an interface to applications and end users and manages computing resources by keeping track of resource usage and grant/ revoke permissions for resources as well as it executed software. 

Examples for operating systems

• Windows
• Linux 
• Android 

Evolution of Operating System

1.No OS(late 1940- mid 1950s)

An operating system was not uses in this area. Therefore users had to give each and every instruction step by step.

Feature of this instructions

• No operating system.
• Processors sat idle when loading programs and doing I/O
• uniprogramming   
• Manual programing Scheduling
• Single user system
• Programs loaded directly into computer

2. Simple Batch System

• These system were introduced to maximize the processor utilization and these programs were recorded in a magnetic tape with an inexpensive machine. 
• OS loaded and executed programs in tape one at a time.
• When the current program ended execution, its output was written to another tape and OS loaded next program.
• At the end of entire batch of programs, output tape was printed with an inexpensive machine.

Features:-

• No direct access to hardware 
• Uniprogramming 
• Processor sat idle during I/O
• High response time

3.Multi-programmed batch System 

• These system can be taken as a Central theme of modern OS and were introduced in 3rd generation computers to minimized the processor idle time during input and output.
• Memory is partition to hold multiple programs.
• If memory is large enough to hold more programs, proceeder could keep 100% busy.
• When current program waiting for I/O, OS switches processor to execute another program in the memory.

4.Time Sharing System

A time sharing operating system is that each task is given some time to execute and all tasks are given time, so that all processes run without any traffic.

• Introduced to minimize the response time and maximize the user interaction during program execution and it uses context switching method(process switch/ task switch) which means CPU switch one process to another process.
• Enables to share the process time among multiple programs. 

Main functions of an operating system

• Process Management(by allocating time for processes)

• Resources Management(Memory, I/O device, storage)

• Providing a user Interfe.

• Managing Security and Access rights for the protection of the computer system.

Different Types of operating system 

computer operating system cab be categorized according to the number of users and number of tasks.

Different types of operating system(Based on the users)

• single user- Facilitates single user to use the system at a time.
• Multi user- Facilities multiple users to use the system at a time.

Different types of operating system(Based on Number of tasks)

• Single Task- Executes only one program at a time.
• Multi Task- Executes multiple program at a time.

Other types of operating systems

• Single user-single task- A single task is performed by one user at a time

• Single user-multi task- Several programs are run at the same time by a single user.

• Multi user- Multi task- A multi- user operating system has been design for more than one user to access the computer at the same time or different time.

• Multi-threading- A thread is also called a sub process. Threads provide a way to improve application performance through the parallel execution of sub process.

Real time- 

• OS is design to run applications with very precise timing and with high degree of reliability.

• The main objective of real-time operating system is their quick and predictive response to event.

• These type of OS are needed in situations where downtime is costly or a program delay could cause a safety hazard.

Time sharing System 

• Processor's time is shared among multiple users/applications. 

• Provides quick response

• Reduced CPU idle time.