Sistemet Operative

Shembuj Sistemesh Operative

Ka shume sisteme operative ne treg me pagese ose me kod burimi te hapur (open source). Me poshte po listojme disa shembuj sistemesh operative:

• Windows, sistem operativ i Microsoft per kompjutera dhe servera

• Linux nje version i bazuar mbi sistemin operativ  Unix  publikuar per here te parene shtatot , 1991 ngaLinus Torvalds. Sot ka me shume se 30+ variante si Fedora, OpenSUSE, CentOS, UBuntu etj.  Shume prej tyre jane pa pagese ndersa mund te kene versione "enterprise" me pagese.

• MacOS, sistem operativ mobile i zhvilluar nga Apple Inc. per pajisjet e tyre

• iOS , sistem operativ mobile i zhvillia nga Apple Inc. i perdorur vetem per pajisjet e tyre mobile siiPhone, iPad etj.

• Android, sistem operativ mobile i bazuar ne nje version te modifikuar te kernel te Linux dhe disa software te tjere me kod burimi te hapur i ndertuar kryesisht per pajisje mobile me prekje(touch) si telefone, tableta, televozore, pajisje te levizshme etj

Sisteme te tjere me te vjeter por ende e perdorim, nder te cilet Solaris, VMS, OS/400, AIX, z/OS, etj

Funksionet  e Sistemit Operativ

Funksionet e sistemeve operative jane:

• Administrimi i proceseve

• Administrimi i pajisjeve te hyrje/daljes 

• Administrimi i skedareve 

• Administrimi i rrjetit

• Administrimi i Memories baze 

• Administrimi i memorjes dytesore 

• Administrimi i sigurise 

• Interpretimi i komandave te sistemit 

• Kontroll mbi performancen e sistemit

• Skedulimi i Pneve

• Kapja dhe korrigjimi i gabimeve

• etj

Batch Operating Systems

The users of a batch operating system do not interact with the computer directly. Each user prepares his job on an off-line device like punch cards and submits it to the computer operator. To speed up processing, jobs with similar needs are batched together and run as a group. The programmers leave their programs with the operator and the operator then sorts the programs with similar requirements into batches.

The problems with Batch Systems are as follows −

Lack of interaction between the user and the job.

CPU is often idle, because the speed of the mechanical I/O devices is slower than the CPU.

Difficult to provide the desired priority.

The users of a batch operating system do not interact with the computer directly. Each user prepares his job on an off-line device like punch cards and submits it to the computer operator. To speed up processing, jobs with similar needs are batched together and run as a group. The programmers leave their programs with the operator and the operator then sorts the programs with similar requirements into batches.

Time-sharing operating systems

Time-sharing is a technique which enables many people, located at various terminals, to use a particular computer system at the same time. Time-sharing or multitasking is a logical extension of multiprogramming. Processor's time which is shared among multiple users simultaneously is termed as time-sharing.

The main difference between Multiprogrammed Batch Systems and Time-Sharing Systems is that in case of Multiprogrammed batch systems, the objective is to maximize processor use, whereas in Time-Sharing Systems, the objective is to minimize response time.

Multiple jobs are executed by the CPU by switching between them, but the switches occur so frequently. Thus, the user can receive an immediate response. For example, in a transaction processing, the processor executes each user program in a short burst or quantum of computation. That is, if n users are present, then each user can get a time quantum. When the user submits the command, the response time is in few seconds at most.

The operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time. Computer systems that were designed primarily as batch systems have been modified to time-sharing systems.

Advantages of Timesharing operating systems are as follows −

Provides the advantage of quick response.

Avoids duplication of software.

Reduces CPU idle time.

Disadvantages of Time-sharing operating systems are as follows −

Problem of reliability.

Question of security and integrity of user programs and data.

Problem of data communication.

Distributed operating System

Distributed systems use multiple central processors to serve multiple real-time applications and multiple users. Data processing jobs are distributed among the processors accordingly.

The processors communicate with one another through various communication lines (such as high-speed buses or telephone lines). These are referred as loosely coupled systems or distributed systems. Processors in a distributed system may vary in size and function. These processors are referred as sites, nodes, computers, and so on.

The advantages of distributed systems are as follows −

With resource sharing facility, a user at one site may be able to use the resources available at another.

Speedup the exchange of data with one another via electronic mail.

If one site fails in a distributed system, the remaining sites can potentially continue operating.

Better service to the customers.

Reduction of the load on the host computer.

Reduction of delays in data processing.

Network operating System

A Network Operating System runs on a server and provides the server the capability to manage data, users, groups, security, applications, and other networking functions. The primary purpose of the network operating system is to allow shared file and printer access among multiple computers in a network, typically a local area network (LAN), a private network or to other networks.

Examples of network operating systems include Microsoft Windows Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell NetWare, and BSD.

The advantages of network operating systems are as follows −

Centralized servers are highly stable.

Security is server managed.

Upgrades to new technologies and hardware can be easily integrated into the system.

Remote access to servers is possible from different locations and types of systems.

The disadvantages of network operating systems are as follows −

High cost of buying and running a server.

Dependency on a central location for most operations.

Regular maintenance and updates are required.

Real Time operating System

A real-time system is defined as a data processing system in which the time interval required to process and respond to inputs is so small that it controls the environment. The time taken by the system to respond to an input and display of required updated information is termed as the response time. So in this method, the response time is very less as compared to online processing.

Real-time systems are used when there are rigid time requirements on the operation of a processor or the flow of data and real-time systems can be used as a control device in a dedicated application. A real-time operating system must have well-defined, fixed time constraints, otherwise the system will fail. For example, Scientific experiments, medical imaging systems, industrial control systems, weapon systems, robots, air traffic control systems, etc.

There are two types of real-time operating systems.

Hard real-time systems

Hard real-time systems guarantee that critical tasks complete on time. In hard real-time systems, secondary storage is limited or missing and the data is stored in ROM. In these systems, virtual memory is almost never found.

Soft real-time systems

Soft real-time systems are less restrictive. A critical real-time task gets priority over other tasks and retains the priority until it completes. Soft real-time systems have limited utility than hard real-time systems. For example, multimedia, virtual reality, Advanced Scientific Projects like undersea exploration and planetary rovers, etc.

Sherbimet e sistemit operativ

An Operating System provides services to both the users and to the programs.

It provides programs an environment to execute.

It provides users the services to execute the programs in a convenient manner.

Following are a few common services provided by an operating system −

• Program execution

• I/O operations

• File System manipulation

• Communication

• Error Detection

• Resource Allocation

• Protection

Program execution

Operating systems handle many kinds of activities from user programs to system programs like printer spooler, name servers, file server, etc. Each of these activities is encapsulated as a process.

A process includes the complete execution context (code to execute, data to manipulate, registers, OS resources in use). Following are the major activities of an operating system with respect to program management −

Loads a program into memory.

Executes the program.

Handles program's execution.

Provides a mechanism for process synchronization.

Provides a mechanism for process communication.

Provides a mechanism for deadlock handling.

I/O Operation

An I/O subsystem comprises of I/O devices and their corresponding driver software. Drivers hide the peculiarities of specific hardware devices from the users.

An Operating System manages the communication between user and device drivers.

I/O operation means read or write operation with any file or any specific I/O device.

Operating system provides the access to the required I/O device when required.

File system manipulation

A file represents a collection of related information. Computers can store files on the disk (secondary storage), for long-term storage purpose. Examples of storage media include magnetic tape, magnetic disk and optical disk drives like CD, DVD. Each of these media has its own properties like speed, capacity, data transfer rate and data access methods.

A file system is normally organized into directories for easy navigation and usage. These directories may contain files and other directions. Following are the major activities of an operating system with respect to file management −

Program needs to read a file or write a file.

The operating system gives the permission to the program for operation on file.

Permission varies from read-only, read-write, denied and so on.

Operating System provides an interface to the user to create/delete files.

Operating System provides an interface to the user to create/delete directories.

Operating System provides an interface to create the backup of file system.

Communication

In case of distributed systems which are a collection of processors that do not share memory, peripheral devices, or a clock, the operating system manages communications between all the processes. Multiple processes communicate with one another through communication lines in the network.

The OS handles routing and connection strategies, and the problems of contention and security. Following are the major activities of an operating system with respect to communication −

Two processes often require data to be transferred between them

Both the processes can be on one computer or on different computers, but are connected through a computer network.

Communication may be implemented by two methods, either by Shared Memory or by Message Passing.

Error handling

Errors can occur anytime and anywhere. An error may occur in CPU, in I/O devices or in the memory hardware. Following are the major activities of an operating system with respect to error handling −

The OS constantly checks for possible errors.

The OS takes an appropriate action to ensure correct and consistent computing.

Resource Management

In case of multi-user or multi-tasking environment, resources such as main memory, CPU cycles and files storage are to be allocated to each user or job. Following are the major activities of an operating system with respect to resource management −

The OS manages all kinds of resources using schedulers.

CPU scheduling algorithms are used for better utilization of CPU.

Protection

Considering a computer system having multiple users and concurrent execution of multiple processes, the various processes must be protected from each other's activities.

Protection refers to a mechanism or a way to control the access of programs, processes, or users to the resources defined by a computer system. Following are the major activities of an operating system with respect to protection −

The OS ensures that all access to system resources is controlled.

The OS ensures that external I/O devices are protected from invalid access attempts.

The OS provides authentication features for each user by means of passwords.