WHAT IS OS (OPERATING SYSTEM)? EXPLAIN OBJECTIVES, FUNCTIONS, TYPES OF O.S.?BJECTIVES,

Definition of Operating System:

1.    An operating system (OS) is a software, that manages the computer hardware, and provides common services for execution of various application software.  For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between application programs and the computer hardware .

2.    An operating system (sometimes abbreviated as "OS") is the program that, after being initially loaded into the computer by a boot program, manages all the other programs in a computer.

Objectives of Operating System:

1.    Convenience: makes computer user friendly.

2.    Efficiency: allows computer to use resources efficiently.

3. Ability to evolve: constructed in a way to permit effective development, testing and introduction of new functions without interfering with service.

 

Functions of Operating System:

1.    Resource Management:  The resource management function of an OS allocates computer resources such as CPU time, main memory, secondary storage, and input and output devices for use.

a.     Process Management:  The operating system is responsible for the following activities in connection with process management:

                                                             i.      Creating and deleting both user and system processes.

                                                          ii.      Suspending and resuming processes.

                                                       iii.      Providing mechanisms for process synchronization.

                                                       iv.      Providing mechanisms for process communication.

                                                          v.      Providing mechanisms for deadlock handling.

b.    Memory Management:  The operating system is responsible for the following activities in connection with memory management:

                                                             i.      Keeping track of which parts of memory are currently being used and by whom.

                                                          ii.       Deciding which processes and data to move into and out of memory.

                                                       iii.      Allocating and deallocating memory space as needed.

 

c.     Storage Management:

                                                             i.      File – System Management:  The operating system is responsible for the following activities in connection with the file management:

·       Creating and deleting files

·       Creating and deleting directories to organize files.

·       Supporting primitives for manipulating files and directories.

·       Mapping files onto secondary storage.

·       Backing up files on stable (nonvolatile) storage media.

                                                          ii.      Mass – Storage Management:  The operating system is responsible for the following activities in connection with disk management:

·       Free-space Management

·       Storage Allocation

·       Disk Scheduling.

d.    Device Management: One of the purposes of operating system is to hide the peculiarities of specific hardware devices from the user.

2.    Data Management:  The data management functions of an OS govern the input and output of the data and their location, storage, and retrieval.

3.    Job Management:  The job management function of an OS prepares, schedules, controls, and monitors jobs submitted for execution to ensure the most efficient processing. A job is a collection of one or more related programs and their data.

4.    Standard means of communication between user and computer:  The OS establishes a standard means of communication between users and their computer systems. It does this by providing a user interface and a standard set of commands that control the hardware.

5.  In a multitasking operating system where multiple programs can be running at the same time, the operating system determines which applications should run in what order and how much time should be allowed for each application before giving another application a turn.

6.  It manages the sharing of internal memory among multiple applications.

7.  It handles input and output to and from attached hardware devices, such as hard disks, printers, and dial-up ports.

8. It sends messages to each application or interactive user (or to a system operator) about the status of operation and any errors that may have occurred.

9. It can offload the management of what are called batch jobs (for example, printing) so that the initiating application is freed from this work.

10. On computers that can provide parallel processing, an operating system can manage how to divide the program so that it runs on more than one processor at a time.

11. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.

12. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.

 

Types of Operating System:

1.    Batch Operating System:  Batch operating system is the operating system which analyzes your input and groups them into batches i.e. data in each batch is of similar characteristics. And then it performs operation on each individual batch.

2.    Real-time:  A real-time operating system is a multitasking operating system that aims at executing real-time applications. Real-time operating systems often use specialized scheduling algorithms so that they can achieve a deterministic nature of behavior. The main object of real-time operating systems is their quick and predictable response to events. They either have an event-driven or a time-sharing design. An event-driven system switches between tasks based on their priorities while time-sharing operating systems switch tasks based on clock interrupts.

a.   Hard real-time system:  It has the most stringent requirements, guaranteeing that real-time tasks be completed within their deadlines. Safety-critical systems are typically hard real-time systems.

b.    Soft real-time system:  It is less restrictive, simply providing that a critical real-time task will receive priority over other tasks and that it will retain that priority until it completes. Many commercial operating systems – as well as Linux – provide soft real-time support.

3.    Multi-user vs. Single-user:  A multi-user operating systemallows multiple users to access a computer system concurrently. Time-sharing system can be classified as multi-user systems as they enable a multiple user access to a computer through the sharing of time. Single-user operating systems, as opposed to a multi-user operating system, are usable by a single user at a time. Being able to have multiple accounts on a Windows operating system does not make it a multi-user system. Rather, only the network administrator is the real user. But for a Unix-like operating system, it is possible for two users to login at a time and this capability of the OS makes it a multi-user operating system.

4.    Multi-tasking vs. Single-tasking:  When a single program is allowed to run at a time, the system is grouped under a single-tasking system, while in case the operating system allows the execution of multiple tasks at one time, it is classified as a multi-tasking operating system. Multi-tasking can be of two types namely, pre-emptive or co-operative. In pre-emptive multitasking, the operating system slices the CPU time and dedicates one slot to each of the programs. Unix-like operating systems such as Solaris and Linux support pre-emptive multitasking. Cooperative multitasking is achieved by relying on each process to give time to the other processes in a defined manner. MS Windows prior to Windows 95 used to support cooperative multitasking.

5.    Single-processor Systems:  On a single-processor system, there is one main CPU capable of executing a general-purpose instruction set, including instructions from user processes.

6.    Multi-processor Systems:  A multiprocessing operating system allows a program to run on more than one central processing unit (CPU) at a time. This can come in very handy in some work environments, at schools, and even for some home-computing situations.

a.    Asymmetric multiprocessing:  In this each processor is assigned a specific task. A master processor controls the system; the other processors either look to the master for instruction or have predefined tasks. This scheme defines a master-slave relationship. The master processor schedules and allocates work to the slave processors.

b.    Symmetric multiprocessing (SMP):  In this each processor performs all tasks within the operating system. SMP means that all processors are peers; no master-slave relationship exists between processors.

7.    Distributed:  A distributed operating system manages a group of independent computers and makes them appear to be a single computer. The development of networked computers that could be linked and communicate with each other, gave rise to distributed computing. Distributed computations are carried out on more than one machine. When computers in a group work in cooperation, they make a distributed system.

8.    Embedded: Embedded operating systems are designed to be used in embedded computer systems. They are designed to operate on small machines like PDAs with less autonomy. They are able to operate with a limited number of resources. They are very compact and extremely efficient by design. Windows CE and Minix 3 are some examples of embedded operating systems.