Os functions

Os functions

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  Definition  Operating systemis a system software that controls the hardware of the computer system and provides an environment for interaction between the user and system.  Simply OS(Operating System) is an intermediary between user and computer hardware.
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  Roles of OS The roles played by the OS can be summarized as follows:-  Resource manager:-Provides efficient, easy and systematic utilization of the resources.  Service provider:-Provides an environment for smooth execution of the other programs of the user.  Interface:-Provides an interface(GUI or DOS) to the user of the computer system.  Examples of OS:-MS-DOS,MS95/98/XP/Vista/7/8,  UNIX, LINUX, Solaris, OS/2 and Mac OS.
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  Functions of OperatingSystem  Following are the functions of operating system: 1. Process Management 2. Memory Management 3. File Management 4. Device Management 5. Security
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  Process Management  ProcessManagement:- In computer system several processes are running at the same time on the CPU, for maximum utilization of CPU. So these all processes are to be properly scheduled to get CPU for execution. OS uses scheduling algorithms for that  Processes are require several resources for execution OS must provide them.  New, ready, running, waiting, finished are states of process.
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  Memory Management  Inmultiprogramming environment main memory is very precious resource, so memory management is one of the very important function of OS.  The OS works as memory manager. The OS ensures the following: 1. Allocation of enough memory space to the individual processes & data at their execution time.
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  2. Optimum useof all kind of available memories. 3. Release of data & processes from the memory once the process is completed.
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  Methods of memoryallocation Contiguous: -Contiguous memory chunks(Blocks) are allocated to the different processes a. Fixed partition b. Variable or Dynamic
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  FIXED PARTITION 40 OS 40 40 40 40OS 20 20 A 40 40 40 OS 20 20 A 30 B 10 40 40 OS 20 20 A 30 B 10 40 C
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  Internal Fragmentation  Infixed partition , the process occupies an entire partition and the unused part of the memory cannot be utilized for other processes.  The unused part is wasted and this problem is called internal fragmentation.
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  VARIABLE PARTITION 30 OS30 OS 20 A 30 OS 20 30 A B 30 OS 20 30 B 60 C 10 30 OS 20 30 B
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  Continue…… 1.As the processA arrives, the chunks of 20KB is allocated to A. 2.Then the process B arrives, the chunk of 30KB is allocated to B. 3. Now the process A is completed so 20KB of A is released as shown in figure. 4. When process C arrives, the chunk of 60KB is allocated to process C as shown in figure, because it does not fit in the recently released 20KB of A and the total memory of 150KB is divided into chunks of varying size ranging from 10KB to 60Kb.
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  External fragmentation.  Iftotal memory is available to accommodate a requesting process, But OS is not allowed this process because this total memory part is not contiguous. The total memory part is available into many different chunks. This problem is called External fragmentation.
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  File management  Afile is a collection of logically related information which can be stored in the memory of the computer system and can be read, write and manipulated.  The OS performs following operations on the file such 1. Creating the file 2. Deleting the file 3. Searching the file 4. Renaming the file 5. Updating the file
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  Continue……….  Characteristics ofa file: 1. Name 2. Location 3. Size 4. Type 5. Date (of last access and creation, modification) 6. Time
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   Device management: 1.-OS is responsible for effective utilization of various I/O devices. 2. A device manager in the OS handles the management of the devices connected to the computer system. 3. OS communicate with the devices through a device driver software. 4. The devices are connected to the computer bia different ports.
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   Security:-OS protectsour system from different kind of external threats. 1. OS provides facility of creating different users, these users are password protected. So, only the user with the valid password can use the account 2. The OS provides sharing of folders and drives on network. We can set access permissions to users on network.
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  Types of operatingsystems Batch operating system:-In this OS a job pool is created by operator according to the need of users, than operator loads the job pool into the main memory and CPU executes the job one by one. These are very slow operating systems. They require trained operator to load jobs into memory and to take results. Sometime CPU sits idle when jobs are busy with input/output.
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   Multiprogramming OS:-Inthis systems multiple processes are allowed to reside in main memory, so CPU can select one of them if currently executing process is want to do I/O. In this system CPU is never sits idle. A scheduler select and deselect processes during execution. These systems are fast.  WIN-98/XP/7
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  Time sharing OS:-Thisis logical extension of multiprogramming OS. CPU switching among processes are very fast, so that each user can execute his/her program without delay. These are also called multitasking OS. Windows NT/2000/XP
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   Real TimeOS:-They are designed for handling real time applications, where quick response in minimum time is very essential. For example, to withdraw money from your nearest ATM, operations of military instruments, traffic control system, online bookng systems etc.  IBM’s OS-9, LINUX, OS/390
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   Network operatingsystem:- These OS provide networking facilities like one can share data and printer on network.  These computer communicate with each other through communication lines.  These OS are designed to install as a server for clients on network.  WINDOWS server 2003 and LINUX are easily configured as a server.