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Operating Systems

In brief, an operating system is the set of programs that controls a computer
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It provides users an environment in which a user can execute programs conveniently
and efficiently
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An operating System controls the allocation of
resources and services such as memory, processors, devices and information
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Main memory is a large array of words or
bytes where each word or byte has its own address
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So for a program to be executed, it must in the main memory
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 Keeps track of primary memory
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 Allocates the memory when the process requests it to do so
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Processor Management
In multiprogramming environment, OS decides which process gets the processor when and how much time
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Operating System does the following activities for processor management
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Program responsible for this task is known as traffic controller
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 De-allocates processor when processor is no longer required
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Operating System does the following activities for device
management
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Program responsible for this task is known as the I/O controller
Decides which process gets the device when and for how much time
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De-allocates devices
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This interface is called an I/O module, which consist of both
hardware and software components
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Software component is the device driver, which controls the I/O device
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Converts the signal type from analog to digital and vice versa
Converts serial to parallel communications and vice versa
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All the processes in the CPU is
blocked until the I/O operation is completed
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Device Polling

Polling is the process where the computer or the controlling device waits for an external device to check for its readiness or
the state often with low level hardware
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Instead it is allowed to execute some other processes for a short period of time and then go check the device states
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Interrupt Driven I/O

In the Interrupt driven scenario, the CPU works on its given tasks continuously
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When an I/O
request is initiated by the CPU, it is simply switched over to another process and continues the execution until the I/O device
send a return signal, which is called an Interrupt
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Therefore the
current process should be interrupt to pay attention to do the data transmission
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The microprocessor is
freed from involvement with the data transfer, thus speeding up overall computer operation
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These directories may contain files and
other directions
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Keeps track of information, location, uses, status etc
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Decides who gets the resources
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De-allocates the resources
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The Resources like Memory and Processor and all the Input output Devices those are attached to the
system are known as the resources of the computer system and the operating system will manage all the resources of the
system
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And which input device will respond to which request of the user means when the input
and output devices are used by the programs
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Other Activities Done
 Security
o By means of password and similar other techniques, preventing unauthorized access to programs and data
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 Job accounting
o Keeping track of time and resources used by various jobs and users
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 Coordination between other software and users
o Coordination and assignment of compilers, interpreters, assemblers and other software to the various users of
the computer systems
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Just as the OS shields the programmer from the
disk hardware, and presents a simple file-oriented interface, it also conceals a lot of unpleasant business
concerning interrupts, timers, memory management, and other low level features
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Types of Operating System
All the operating systems can be categorized as to two components
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For example, the washing
machine’s OS is used to integrate the clothes washing powder and the motor speed so that the clothes are washed properly
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Single User Multi-Tasking
By taking Windows to example, the multi-tasking refers to the ability that it is able to run multiple programs (applications) at
the same time
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They are running
in a time sharing based giving the user the idea of running parallel
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Multiple users can access the computer the same time (Main frame
computers)
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Layered Architecture of a Computer System

There are three kinds of modes when
expanded as the layered architecture
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In the user mode, if
the person doesn’t like the specific
application, they can uninstall it
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This is widely used for system
calls (example: disk interrupt handler)
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A major function of the operating system is to hide all the complexity and give the programmer a more convenient set of
instructions to work with

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