Operating System Overview

Operating System Overview

• OS definition: Operating System is a program that controls the execution of application programs. It is an interface between applications and hardware.

• OS provides different types of view. For user, it is abstract view because it provides features which are important for users. OS is intermediary between user and the computer system.

• The major design goals/ functions of an operating system are :

1. Efficient use of a computer system 2. User convenience 3. Ability to evolve.

• An operating system is software that manages the computer hardware. The hardware must provide appropriate mechanisms to ensure the correct operation of the computer system and to prevent user programs from interfering with the proper operation of the system.

• Efficiency is the one of the parameter for use of computer system. Operating system consumes some resources during its own operation. For example it uses CPU and memory. CPU is busy with scheduling and memory is occupied by instruction and required data.

• This is one type of overhead and because of this lesser resources are available to the user.

• An OS makes a computer more convenient to use. If the operating system can notallocates the free available resources to program or it over allocates the resources then efficiency is poor.

Efficient use

• For efficient use of resources, it must be monitored by operating system. Proper bold scheduling of resources is also required.

• Computer contains different type's resources like CPU, memory and I/O device etc. Proper monitoring is required on these resources to avoid the overhead. As per the resource, scheduling is required.

• Special attention to be given for CPU and memory. If memory is not free then user can not load new program into the memory. Then CPU will be busy with memory management.

User convenience

• User convenience is affected by computing environment of the computer system. The computing environment is comprised of computer system, its interfaces with other systems and nature of computations performed by its users.

• Computer architecture and use change the computing environment of the system. Following factors are considered while considering user convenience:

1. Good service      2. Ease of use       3. New programming model        4. Evolution        5. User friendly OS

Ability to evolve

• An OS should be constructed in such a way as to permit the effective en development, testing and introduction of new system functions without at the same time interfering with service.

• Task performed by operating systems :

1. Maintain the list of resources in the system

2. Maintain the list of authorized users

3. Initiate the execution of programs and process

4. Maintain resource usage list

5. Maintain the resource allocated list

6. Scheduling of resources (CPU, Secondary storage etc.)

7. Also maintain the protection information.

Operating System as a User Interface

• Computer system consists of software and hardware to solve specific problems. User, application program, operating system and the hardware are the components of the computer systems.

• Application program used to solve specific program. Student attendance no no monitoring is the example of application program.

• Operating system is a subset of the system software. OS interacts directly with the hardware to provide an interface to other system software.

• System software and hardware exist to support the creation and effective use application software.

• Fig. 1.2.1 shows conceptual view of a computer system.

• Resource sharing and resource abstraction are two key aspects of the operating system.

• Purposes of the operating system :

1. OS provides an interface between the computer hardware and computer user (programmer). It simplifies the programmer job like editing, coding, creation.

2. Allocation and use of computer resources among the programmer is controlled arnaldo it by OS.

Operating System as Resource Manager

• A computer is a set of resources. These resource provides various functions to the user. Functions like data movement, storing of data and program, operation on data are control by an operating system.

• Fig. 1.2.2 shows OS as a resource manager.

• The operating system is responsible for managing the all resources. A portion of the OS is in main memory. This portion of the OS is called kernel.

• User program and data is also stored in remaining parts of the memory. Allocation of main memory is controlled by operating system with the help of memory management hardware.

• I/O device is controlled by OS and it decides when an I/O device can be used by program in execution. Processor is one type of resource and OS control the execution of user program on the processor.

• Modern OS allows multiple programs to run at the same time. If multiple users are using computer then there is need of managing and protecting the memory, I/O devices and other resources.

• Resource management includes sharing resources in different ways. Time and space are the two concept for resource sharing.

1. Time: Time slot is allocated to each program first one gets to use the resource then another and so on.

2. Space: Consider the example of main memory. Main memory is normally divided up among several running programs, so each one can be resident at the same time.

Characteristics of Modern Operating Systems

1. Microkernel architecture assigns only a few major functions to the kernel. It includes basic CPU scheduling, IPC, allocation of address space etc.

2. Process: Collection of threads.

3. Thread Thread is light weight process. A thread is a flow of execution through the process code. It contains program counter, stack pointer and stack for data storage.

4. Multithreading: Process creates number of multiple threads. These all thread can run simultaneously.