27. Operating System Management

20 May 2020 | CS

Operating System Management

in computer programming, a process is an instance of a computer program that is being currently executed.

A computer program is a passive collection of instructions, while a process is the actual execution of those instruction when operating system allocates the resources(Memory & processor time). several processes may be associated with the same program.

For example : a user may working on number of MS word documents simultaneously.

A process can be user application program Or system process. operating system is responsible to manage both these processes.

A multitasking operating system rapidly switches the CPU execution time between the different processes currently being executed. although, CPU executes only one process at a time but due to switching it creates an illusion that all programs(processes) are running simultaneously but that is not the case

the process management is an important function managed by the operating system. the CPU can execute only one process at a time. therefore, operating system has to decide the schedule for process, order of execution for different processes at various stages and the CPU time to be allocated.

the program execution needs resources in terms of memory and the CPU’s processing time. the operating system manages the memory of the computer system by allocating main memory to different process currently under execution at various stages.

the main memory of also needs to be reallocated from the process that is already terminated. memory is an important limited resource and operating system manages this by allocation and reallocating the memory from terminated process to the new processes

A file is a collection of related information. A file can be text file, image, audio, video and many more.

the data is represented in a computer system only in a binary form. the data is stored permanently in a secondary storage devices such as hard disk

this data is physically stored in hard disk in two states(for magnetic tapes it is south and north poles) which can be represented in the binary form in a computer system.

the operating system is responsible for the following activities in connection with file management.

File creation and deletion

Directory creation and deletion

Support of primitives for manipulating files and directories

Mapping files onto secondary storage

File backup on stable(Non-volatile) storage media.

one of the important responsibility of the operating system is to provide secure and protected runtime environment to the various process(both applications process & system processes) which are being executed on the computer system.

the system security is another important aspect which is handily by the operating system. protecting system against unauthorized access can be implemented by activating different security features of the operating system.

A command interpreter is a program which reads the instructions given by the user. it then translates these instructions into the context of the operating system followed by the execution. command interpreter is also known as “shell”

A command interpreter is the part of a computer operating system that understand and executes commands that are entered interactively by a user or from a program.

A command interpreter is an interface between system and the user. there are two types of user interface:

command line interface

Graphical User Interface(GUI)

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27. Operating System Functions

20 May 2020 | CS

Operating System and operation modules

A computer system can be designed to operate in different modes in terms of number of users working on the machine at the same time, number of processors used, data handling and the number of applications running simultaneously on the same computer system.

A computer system needs to be configured accordingly and the system will also need the operating system which can support such operations.

in batch processing the processing transactions(交易) are executed in a group or batches. No user interaction(相互影响) is required one batch processing in underway.

the next batch is taken for processing only after the first batch is completed this often lead to CPU processing time is not optimally utilized

Example : IMB : OS2

Multi tasking allows more than one program to run concurrently.

the tasks share common processing resources, such as a CPU time and main memory.

in multi tasking process, only one CPU is involved but it switches from one program to another so quickly that it gives an illusion of executing all the programs at the same time.

the multi processor processing makes use of more than one processor in a same system to enhance the system performance. Due to number of processor the system performance is significantly improved. however, all the processes share the same common main memory(RAM)

A computer system with multi processor needs operating system which can support multiple programs execution simultaneously

A real-time operating system(RTOS commonly pronounced as “are-toss”) is a multitasking operating system designed for real-time applications. Such applications include embedded systems, industrial robots, scientific research equipment and others.

A real-time computing guarantees response within specific time limits and thus suitable for quick reaction system.

Hard Real-time operating systems

Meets deadlines with zero degree of flexibility

Missed deadlines cause catastrophe(灾难)

Cost of catastrophe is high

Soft Real-time operating system

Meets deadlines with some degree of flexibility

Missed deadlines does not cause catastrophe

cost rise in proportion of the delay

the real-time systems are sued in the situations where a large number of events(generally external to the computer system) are required to be accepted and processed in the form of quick response. such systems should be a multitasking system.

Almost all the modern telecommunication systems make use of RTOS

Radar systems, network switching control system, satellite monitoring system, satellite launch-control and manoeuvring(手段) mechanisms, global positioning system all have their operational dependence on RTOS

Now a days RTOS is increasingly finding use in strategic and military operations. there are used in guided missile launching units, track-and-trace spy satellite

Multi user operating system is a computer operating system(OS) that allows multi users to access a single system with one OS managing the computer system.

Each user is given a separate login credentials and more than one user can simultaneously use the computer system. each user will have their own settings.

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26. Operating System architecture

20 May 2020 | CS

Operating System architecture

An operating system structure(OS design approach/architecture) can be classified based on the design approach and implementation by the operating system.

simple structure OS

layered approach OS

Monolithic Approach OS

Microkernel Approach OS

Monolithic((组织或体系) 庞大而僵化的) Kernel Design

A kernel is the central part of an operating system with unrestricted access to all system recourses. it manages the tasks of the computer software and the hardware(most notably(特别) Memory RAM and CPU processing time).

there are two types of kernels:

A Microkernel : which contains only basic functionality

A Monolithic Kernel : which contains many drivers

A computer user never interacts directly with the kernel. the kernel run behind the scenes and user interact with OS GUI interface OR through a command line.

The kernel is the most fundamental part and core an operating system. we can think of kernel as the system program which controls all other application program running on the computer system.

when the computer starts, it goes through some initialization(booting) function, such as checking memory. the kernel handles all the system recourses such as main memory RAM and CPU processing time. the kernel is responsible for allocating and reallocating the system memory which allows application programs to run.

the early kernel designs were based on monolithic architecture in which each component of the operating system was contained within the kernel. Applications could communicate directly with any internal component of the operating system and had unrestricted system access. this kind of layered design was perceived(注意到) to be efficient but prone(易于遭受) for crash.

the core software components of an operating system are collectively known as the kernel. the kernel has unrestricted access to all the system resources of a computer system.

in monolithic architecture, each layer communicates only with the layer immediately above and below it. the lower-level layers provide services to higher-level ones using an interface that hide their implementation

although from efficiency point of view the monolithic kernel will perform very well as such operating systems implementing monolithic kernel will be very efficient.

the most important drawback of the monolithic kernel is the inability(无能) to isolate the other components in the event if one such component crashes endangering the entire system to crash. thus there was a high risk of damage due to erroneous of malicious(恶毒的) code

the summarize, the core components of the operating system are collectively referred as kernel. the kernel has unrestricted access to all the system resources. the kernel also handles all the crucial tasks performed by the operating system.

in computer endangering, computer architecture is a set of rules and methods that describes the functionality, system design specifications, organization and implementation details of a computer systems.

A computer architecture is a design specifications detailing how a set of software and hardware technology standards interact to form a computer system or a platform. in short, computer architecture refers to how a computer system is designed and what technologies it is compatible with.

An operating system is an essential component of the computer system. it is a system program which provides services, resources and runtime environment for application programs running on the computer system.

An operating system architecture is a term that specifies the overall structure of the operating system, its logical components and the logical interrelationships of various components that constitute an operating system.

Microkernel Design

A Microkernel architecture includes only a very small number of bare minimum essential services within the kernel area as an attempt to keep it small, protected and scalable.

the services within Microkernel area typically include the low-level memory management, inter-processes communication and basic process synchronisation to enable processes to cooperate.

as compared to a typical kernel, a Microkernel is designed to be compact and performing only the basic functions universal to all computer systems.

the Microkernel are designed to be intergraded into different operating systems. therefore, Microkernel are highly modular which makes them protected, extensible, portable and scalable.

in Microkernel designs, most operating system components such as process management and device management are placed outside kernel area which execute outside the kernel within a user area with lower level of system access.

the Microkernel design OS is considered to be more stable as the device drivers are moved out to the user space so that OS crash could be avoided in the event of faulty drivers.

in a Microkernel operating system, the OS kernel deals only with the critical activities such as controlling the memory allocation and CPU processing time and nothing else.

Drivers and other functions that monolithic kernels would normally do within the kernel area are moved outside the kernel area to the user area, where they are under control.

in Microkernel architecture, the operating system components placed outside the kernel area can fail without causing the entire operating system to crash.

however placing operating system components outside the kernel area affects the performance and the downside is an increased level of inter-module communication which can degrade system performance

to summarize, the core components of the operating system are collectively referred as kernel. the kernel has unrestricted access to all the system resources. the kernel also handles all the crucial tasks performed by the operating system.

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11.Binary Search - Finding first or last occurrence of a number

20 May 2020 | STL Programming Practice_1

#include <bits/stdc++.h>
#include <iostream>
using namespace std;

int Binarysearch_(int M[], int n, int k, int flag)
{
    int left = 0;
    int right = n-1;
    int mid;

    int result = -1;
    while(left<=right)
    {
        mid = (left+right)/2;
        if (k==M[mid])
        {
            result = mid;
            if (flag == 1) right= mid-1;
            if (flag == 2) left = mid +1;
        }
        else if (k<M[mid]) right = mid - 1;
        else left = mid+1;
    }
    return result;

}

int main()
{
    int A[] = {1,1,1,3,3,3,3,3,3,3,5,6,6,8,9,9};

    int n = sizeof(A)/sizeof(A[0]);
    // 1 == firstOccurance
    // 2 == LastOccurance
    int firstOccurance = Binarysearch_(A,n,3,1);
    int lastOccurance = Binarysearch_(A,n,3,2);

    if(firstOccurance==-1)
    {
        cout << "the element is not in the array";
    }else
    {
        cout << "the element appears "<<lastOccurance-firstOccurance + 1;
    }
    return 0;
}