Main Functions of an Operating System

A separate module of operating system software performs following functions:

• Process Management: A process is a program in execution. During execution a process needs certain resources such as CPU time, memory space and I/O devices. At a particular instance of time, a computer system normally consists of a collection of processes. Process management module take care of creation and deletion of processes, scheduling of system resources to different processes requesting them and providing mechanisms for synchronization and communication among processes.
• Memory Management: To execute a program, it must be loaded in main memory (at least partially) together with the data it accesses. To improve CPU utilization and to provide better response time to its users, a computer system normally keeps several programs in main memory. Memory management module takes care of allocation and de-allocation of memory space to programs in need of  this resource.
• File Management: All computer systems store, retrieve and share information. Normally, a computer stores such information in units called files. Process read information from files and create new files for storing newly generated information. File management modules takes care of file related activities such as organization, storage, retrieval, naming, sharing and protection of files.
• Device Management: Normally, a computer system consists of several I/O devices such as terminal printer, disk and tape. The device management module of an operating system controls all I\O devices. It keeps track of I\O requests from processes, issues commands as I\O devices and ensures correct data transmission to\from an I\O device. It also provides a simple and easy interface between the devices and rest of the system.
• Security: Computer systems often store large amount of information, some of which are highly sensitive and valuable for its users. Users can trust a computer system and rely on it only if its various resources and information stored in it are protected against destruction and unauthorized access. Security modules protects the resources and information of a computer system against destruction and unauthorized access. It also ensures that when the system executes several disjoint processes simultaneously, one process does not interfere with others or with the operating system itself.
• Command Interpretation: Command interpretation module interprets user commands and directs system resources to process the commands.  

Data Communication

Data communication refers to the exchange of data between a source and a receiver. Data communication is said to be local if communicating devices are in the same building or a similarly restricted geographical area.

The meanings of source and receiver are very simple. The device that transmits the data is known as source and the device that receives the transmitted data is known as receiver. Data communication aims at the transfer of data and maintenance of the data during the process but not the actual generation of the information at the source and receiver.

Datum mean the facts information statistics or the like derived by calculation or experimentation. The facts and information so gathered are processed in accordance with defined systems of procedure. Data can exist in a variety of forms such as numbers, text, bits and bytes. The Figure is an illustration of a simple data communication system.

A data communication system may collect data from remote locations through data transmission circuits, and then outputs processed results to remote locations. Figure provides a broader view of data communication networks. The different data communication techniques which are presently in widespread use evolved gradually either to improve the data communication techniques already existing or to replace the same with better options and features. Then, there are data communication jargons to contend with such as baud rate, modems, routers, LAN, WAN, TCP/IP, ISDN, during the selection of communication systems. Hence, it becomes necessary to review and understand these terms and gradual development of data communication methods.

Components of data communication system

1. Message: It is the information or data to be communicated. It can consist of text, numbers, pictures, sound or video or any combination of these.

2. Sender: It is the device/computer that generates and sends that message.

3. Receiver: It is the device or computer that receives the message. The location of receiver computer is generally different from the sender computer. The distance between sender and receiver depends upon the types of network used in between.

4. Medium: It is the channel or physical path through which the message is carried from sender to the receiver. The medium can be wired like twisted pair wire, coaxial cable, fiber optic cable or wireless like laser, radio waves, and microwaves.

5. Protocol: It is a set of rules that govern the communication between the devices. Both sender and receiver follow same protocols to communicate with each other

A protocol performs the following functions:

1. Data sequencing: It refers to breaking a long message into smaller packets of fixed size. Data sequencing rules define the method of numbering packets to detect loss or duplication of packets, and to correctly identify packets, which belong to same message.

2. Data routing: Data routing defines the most efficient path between the source and destination.

3. Data formatting: Data formatting rules define which group of bits or characters within packet constitute data, control, addressing, or other information.

4. Flow control: A communication protocol also prevents a fast sender from overwhelming a slow receiver. It ensures resource sharing and protection against traffic congestion by regulating the flow of data on communication lines.

5. Error control: These rules are designed to detect errors in messages and to ensure transmission of correct messages. The most common method is to retransmit erroneous message block. In such a case, a block having error is discarded by the receiver and is retransmitted by the sender.

6. Precedence and order of transmission: These rules ensure that all the nodes get a chance to use the communication lines and other resources of the network based on the priorities assigned to them.

7. Connection establishment and termination: These rules define how connections are established, maintained and terminated when two nodes of a network want to communicate with each other.

8. Data security: Providing data security and privacy is also built into most communication software packages. It prevents access of data by unauthorized users.

9. Log information: Several communication softwares are designed to develop log information, which consists of all jobs and data communications tasks that have taken place. Such information may be used for charging the users of the network based on their usage of the network resources.

Information Systems Security

Computer system threats come in many different forms. Some of the most common threats today are software attacks, theft of intellectual property, identity theft, theft of equipment or information, sabotage, and information extortion. Most people have experienced software attacks of some sort. Viruses, worms, phishing attacks, and trojan horses are a few common examples of software attacks. The theft of intellectual property has also been an extensive issue for many businesses in the IT field. Intellectual property is the ownership of property usually consisting of some form of protection. Theft of software is probably the most common in IT businesses today. Identity theft is the attempt to act as someone else usually to obtain that person's personal information or to take advantage of their access to vital information. Theft of equipment or information is becoming more prevalent today due to the fact that most devices today are mobile. Cell phones are prone to theft and have also become far more desirable as the amount of data capacity increases. Sabotage usually consists of the destruction of an organization′s website in an attempt to cause loss of confidence to its customers. Information extortion consists of theft of a company′s property or information as an attempt to receive a payment in exchange for returning the information or property back to its owner. There are many ways to help protect yourself from some of these attacks but one of the most functional precautions is user carefulness.

Governments, military, corporations, financial institutions, hospitals and private businesses amass a great deal of confidential information about their employees, customers, products, research and financial status. Most of this information is now collected, processed and stored on electronic computers and transmitted across networks to other computers.

Should confidential information about a business' customers or finances or new product line fall into the hands of a competitor or a black hat hacker, a business and its customers could suffer widespread, irreparable financial loss, as well as damage to the company's reputation. Protecting confidential information is a business requirement and in many cases also an ethical and legal requirement. A key concern for organizations is the derivation of the optimal amount to invest, from an economics perspective, on information security. The Gordon-Loeb Model provides a mathematical economic approach for addressing this latter concern.

For the individual, information security has a significant effect on privacy, which is viewed very differently in different cultures.

The field of information security has grown and evolved significantly in recent years. There are many ways of gaining entry into the field as a career. It offers many areas for specialization including securing network(s) and allied infrastructure, securing applications and databases, security testing, information systems auditing, business continuity planning and digital forensics.

Database Management System

A database management system (DBMS) is a set of program that allows the creation of datafile, the alteration of the data in these files and the extraction of date from the files. The idea with a DBMS is that all the data is kept centrally and only authorized system can access data via the DBMS.

All database management systems allow the following:

• data files to be set up by creating tables (or datafiles) which may be linked together
• users to ask queries of the data e.g search for data meeting certain criteria
• addition of more data (appending), deletion and editing of existing data
• alteration to the structures of the datafiles or tables
• security by allowing only certain people access to each of the datafiles or tables
• user to import data into the database from other packages and data to be transferred to another package (exporting)

File Organization

There are several methods to organize file.

• Serial Files: Here records don't follow each other in any particular order, if another record needs to be added it can just be added to the end of the file.

• Sequential Files: They are like serial files except the the records are held in a certain sequence e.g to order pupil file in admission number sequence

• Random Files: Random files have to be stored on disk and they are not stored in any order on the disk surface. The disk operating system keeps a map of the disk surface and using this map the read/write heads can go straight to the data. In this way, the data is found without the whole disk having to be read. Random access allows data stored on disk to be found extremely quick.

User Interfaces

The user interface is what you see when you turn on the computer;it consists of cursors, prompts, icons, menus etc which allows you to get something done using your computer.
User interfaces may be:

• command-driven
• menu-driven
• graphical user

Command-driven Interface

With command-driven interface, you type in an instruction (which is usually abbreviated) in order to get something done.Command-driven user interfaces are not easy to use.You have to remember many commands. 

Menu-Driven Interface

It produces a list of commands or options available within a program and the user can make a selection by using either a mouse or a keyboard. Both Microsoft Windows and Apple Macintosh programs are menu driven.

Graphical User Interface

It provides a way for the user to communicate with the computer through pictures (icon) and through pull-down menus. Windows is an example of a GUI. Windows provides a common way of using programs, which make them easier to learn. It also take care of some common chores such as working with printer and disk drive.Apple Macintosh computers were amongst the first to use a GUI.

Operating Systems

An operating system is a program that controls the hardware directly.It provides an interface between user and the computer hardware.It performs following tasks:

• provides a way for application software to communicate with the hardware
• manages the system resources
• manages the transfer of data to and from the various peripherals
• manages system security
• allocates certain rights to users 

Examples: Windows Millennium Edition, Windows 2000, Windows NT, Unix and OS2

Types of operating systems

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 objective of real-time operating systems is their quick and predictable response to events. They have an event-driven or time-sharing design and often aspects of both. An event-driven system switches between tasks based on their priorities or external events while time-sharing operating systems switch tasks based on clock interrupts.[citation needed] Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources.

Multi-user: A multi-user operating system allows multiple users to access a computer system at the same time. Time-sharing systems and Internet servers can be classified as multi-user systems as they enable multiple-user access to a computer through the sharing of time. Single-user operating systems have only one user but may allow multiple programs to run at the same time.[citation needed]

Multi-tasking vs single-tasking: A multi-tasking operating system allows more than one program to be running at the same time, from the point of view of human time scales. A single-tasking system has only one running program. Multi-tasking can be of two types: pre-emptive and 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, as does AmigaOS. Cooperative multitasking is achieved by relying on each process to give time to the other processes in a defined manner. 16-bit versions of Microsoft Windows used cooperative multi-tasking. 32-bit versions of both Windows NT and Win9x, used pre-emptive multi-tasking. Mac OS prior to OS X used to support cooperative multitasking.[citation needed]

Distributed: Distributed system: 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.

Templated: In an OS, distributed and cloud computing context, templating refers to creating a single virtual machine image as a guest operating system, then saving it as a tool for multiple running virtual machines (Gagne, 2012, p. 716). The technique is used both in virtualization and cloud computing management, and is common in large server warehouses.

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.

Data Storing

Computer Systems store data in two store:
1) Main Store e.g chips in side the centre processing unit
2) Backing Store e.g magnetic disk

Main Store (Memory)
Here data is held temporarily while processing takes place. The data held in the memory is instantly available to the computer unlike backing storage which has to be accessed on disk or tape.
There are two types of memory or main store:

• read only memory (RAM)
• random access memory (ROM)