Operating System Services.

• An Operating System is an interface between a user and computer hardware. An operating system is a software which performs all the basic tasks like file management, memory management, process management, input and output devices management, and much more.
• Let's discuss about its services in details...

• Memory management.
• Process Management.
• File Management.
• Program Execution.
• I/O device Management.
• Resource allocation.
• Secondary-Storage Management.
• Network Management.
• Error Detection.
• Protection (User Authentication).

1. Memory Management

• Memory management is the most important part of an operating system and manages both the primary (known as the main memory) and the secondary memory directly. 
• Main memory provides the storage for a program which can be directly accessed by the CPU for its exertion. 
• Therefore, the primary memory management function for a program to be executed is to load the program into main memory.
• Memory management performs mainly two functions, these are..

1. Keep track of which part of memory are currently being used and by whom.
2. Decide which processes should be loaded into memory when the memory space is free.
3. Allocate and de-allocate memory spaces as and when required.

• The operating system loads the instructions into the main memory and then picks up those instructions and makes a queue to get CPU time to execute them. 
• The memory manager monitors which memory locations are open, which are to be allocated or de-allocated.
• It also makes decisions about which pages to swap between the main memory and the secondary memory. 
• This operation is referred to as virtual memory management that increases each process's amount of memory available.

2. Process Management

• In multiprocessing the operating system allows simultaneous running of more than one program (or process). 
• Process management is a part of an operating system that manages the processes in such a way just to improve system performance.
• The operating system deals with other types of activities also that includes user programs and system programs like as printer spooling virtual memory, swapping etc.
• A process is an activity which needs certain resources to fulfill its task. Diverse machine resources include CPU power, main memory, and I / O tools. 
• Those resources are allocated to the processes and are based on the decision that which process should be designated for resource allocation and this decision is taken by process management applying the algorithms for process scheduling.
• It should be remembered that a procedure is not a system. A method is only ONE instant of an operating program. A lot of processes run the same program.
• The five major activities of an operating system in regard to process management are:

1. Creation and deletion of user and system processes.
2. Suspension and re-activation of processes.
3. Process synchronization.
4. Process communication.
5. Deadlock handling.

3. File Management

• A file is a set of related information which its creator defines. Computer can store files on the disk (secondary storage) providing storage for the long term. 
• Magnetic tape, magnetic disk, and optical disk are some examples of storage media. Each of these media has its own properties, such as speed, power, data transfer rate and method of access.
• Typically a file system is organized into directories to make its use simple. These directories may include files, as well as other directories. 
• Each file system consists of analogous directories and sub-directories. Microsoft separates its directories with a back slash and its file names are not case sensitive, while operating systems derived from Unix (including Linux) use the forward slash and its file
• The main file management activities of an operating system are the creation and deletion of files / folders, file / folders manipulation support, file mapping to secondary storage and file backup.

4. Program Execution

• The purpose of the computer system is to enable efficient execution of programs by users. The operating system provides an environment in which those programs can be run smoothly to the user. 
• The user does not have to worry about the allocation or de-allocation of memory or anything else, because the operating system takes care of these things.
• The program must first be loaded into the RAM to run a program, and then assign CPU time to execute it. 
• This function is performed by operating system for user convenience. It also performs other significant tasks such as memory allocation and de-allocation, CPU scheduling etc.

5. I/O Device Management

• Management of input / output device is part of an operating system that provides an environment for improved interaction between system and I / O devices (such as printers, tape drives for scanners, etc.). 
• The operating system requires certain special programs known as the application driver to communicate efficiently with the I / O machines. 
• A system driver is a specific type of computer software designed to allow hardware devices to communicate with it. 
• It usually constitutes an interface for the connection of the hardware to the I / O device, via the actual machine bus or communication subsystem.

6. Resource Allocation

• In the multitasking environment, when multiple jobs are running at a time, it is the responsibility of an operating system to allocate the required resources (like as CPU, main memory, tape drive or secondary storage etc.) to each process for its better utilization. For this purpose various types of algorithms are implemented such as process scheduling, CPU scheduling, disk scheduling etc.

7. Secondary Storage Management

• A computer system has multiple storage levels including main storage, secondary storage, and cache storage. 
• But it is not possible to use primary storage and cache storage as permanent storage because these are volatile memories and their data is lost when power is turned off. 
• The main memory is too small to accommodate both data and programs. So the computer system has to provide secondary storage for the primary memory backup. Secondary storage involves video tapes, disk drives, and other files.
• The secondary storage management provides an easy access to the file and folders placed on secondary storage using several disk scheduling algorithms.
• The four major activities of an operating system in regard to secondary storage management are:

1. To managing free space available on the secondary-storage device.
2. Allocation of storage space.
3. Scheduling the requests for memory access.
4. Creation and deletion of files.

8. Network Management

• When multiple computers are in a network or in a distributed architecture, an operating system functions as a network resource manager.
• Processors communicate with each other through communication lines called network 
• The design of the communication network must consider routing and network methods, as well as network and security issues.
• Many of today's networks are focused on configuration of client-servers. 
• A client is a program running on the local machine requesting the service from a server, while a server is a program running on the remote machine providing customer service by responding to their request.

9. Error Detection

• Operating system also addresses problems with the hardware. The operating system continuously tracks the system to detect the errors and correct those errors to prevent hardware problems. 
• The main function of the operating system is to detect the errors on hard disk such as bad sectors, memory overflow and I / O device-related errors. 
• After the errors are detected, the operating system takes appropriate action to ensure consistent computing.
• User programs can not handle this service of error detection and error correction, because it involves monitoring the entire process of computing. 
• Such functions are too important to transfer to consumer systems. If given these privileges, a user program can interfere with the operation of the operating systems in question.

10. Protection (Authentication)

• Protection is the most demanding feature of an operating system. 
• Protection is an ability to authenticate the users for an illegal access of data as well as system.
• Operating system provides various data and network security services through passwords, file permissions, and data encryption. 
• Computers are generally connected via a network or internet connection, allowing users to share their files and access websites and transfer their files over the network. A high level of security is required for these cases.
• There are various firewalls for the software at the operating system level. A firewall is setup to allow or deny traffic to a service that runs on top of the operating system. 
• Therefore by installing the firewall one can deal with running the services, such as telnet or ftp, and not worry about Internet threats because the firewall will reject any traffic trying to connect to the service on that port.
• If a computer system has multiple users and allows multiple processes to be executed simultaneously, then the different processes must be protected against each other's activities. 
• Protection refers to mechanism for controlling access to the resources defined by a computer system by programs, processes, or users.