Multitasking/Multi programming operating system

Multitasking: - Multiprogramming is a fundamental form of parallel process in which several programs are run at the same time on a processor. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for that task. Multitasking solves the problem by scheduling which task may be the one running at any given time, and when another waiting task gets a turn. The most commonly used personal computers usually run such OSs; include MS WINDOWS and the MACHINTOSH operating system.

Operating system & functions of it

Operating system: - An operating system (OS) is software, consisting of programs and data, which runs on computers, manages computer hardware resources, and provides common services for execution of various application software. The operating system is the most important type of system software in a computer system. Without an operating system, a user cannot run an application program on their computer, unless the application program is self booting.

According to the American National Standards Institute- software which controls the execution of a computer programs and which may provide scheduling, debugging, input/output controls, accounting, compilation, storage assignment, data management and related services.

The functions of operating system-

Displays the on screen element with which you interact- the user interface

Loads programs into the computers memory so that you can use them.

Coordinates how programs work with the computer’s hardware and other software.

Manages the way information is stored on and retrieved from disc.

Asynchronous and Synchronous Data transmission

The basic difference between asynchronous and synchronous data transmission mood are given below-

1. In Asynchronous transmission, data is transmitted character by character; in synchronous transmission, data is transmitted by a group of character.
2. In Asynchronous transmission, data is transmitted at irregular time intervals; in synchronous data is transmitted at regular time intervals.
3. Asynchronous transmission is connection less; synchronous transmission is connection oriented.
4. In Asynchronous transmission a start bit and a stop bit is added to each data segment; in synchronous transmission system start and stop bit are eliminated. Each block framed by header and trailer information.
5. Asynchronous transmission takes much time then synchronous.

OSI model

OSI model: The Open Systems Interconnection model (OSI model) was a product of the open system effort at the International Organization for Standardization.

Open system interconnection is divided into 7 layers.

1.      Physical Layer: The Physical Layer defines electrical and physical specifications for devices. In particular, it defines the relationship between a device and a transmission medium, such as a copper or optical cable. This layer specifies what will be the system speed, modem speed and what will be the voltage level.

2.      Data Link Layer: The Data Link Layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical Layer.

3.      Network Layer: The Network Layer provides the functional and procedural means of transferring variable length data sequences from a source host on one network to a destination host on a different network.

4.      Transport Layer: The Transport Layer provides transparent transfer of data between end users, providing reliable data transfer services to the upper layers. 

5.      Session Layer: The Session Layer controls the dialogues (connections) between computers. It establishes, manages and terminates the connections between the local and remote application. It provides for full-duplex, half-duplex, or simplex operation, and establishes check pointing, adjournment, termination, and restart procedures.

6.      Presentation Layer: The Presentation Layer establishes context between Application Layer entities, in which the higher-layer entities may use different syntax and semantics if the presentation service provides a mapping between them.

7.      Application Layer: The Application Layer is the OSI layer closest to the end user, which means that both the OSI application layer and the user interact directly with the software application. 

Network topology

By which one computer is connected to another or more computer is called network topology. Network topology is the layout pattern of interconnections of the various elements of a computer. In communication networks, a topology is a usually schematic description of the arrangement of a network, including its nodes and connecting lines.

Some topology’s are: - Star topology, Ring topology, completely connected network, Multi-access Bus topology, etc. 

Star topology: - In the star network topology, there is a central computer or server to which all the workstations are directly connected. Every workstation is indirectly connected to every other through the central computer.

The following types of networks are examples of star topologies:

• ARC net

• 10Base-T, 100Base-TX

• Star LAN

Most modern cabling systems are designed in a star physical topology. The

Advantages of the star topology are many, including the following:

1. Easy to implement and extend, even in large networks
2. Well suited for temporary networks (quick setup)
3. The failure of a non central node will not have major effects on the functionality of the network.

However, the big advantage of the star network is that it is fast. This is because each

Computer terminal is attached directly to the central computer.

Star topology has the following disadvantages:

1. Hub failures can disable large segments of the network.
2. Limited cable length and number of stations.
3. Very expensive due to use of a lot of cable.
4. Maintenance costs may be higher in the long run.
5. Failure of the node can disable the entire network.
6. One virus in the network will affect them all.

Ring topology: - The ring topology is a physical, closed loop configuration consisting of point-to-point links. It is a topology of computer networks where each user is connected to two other users, so as to create a ring. A failure in any cable breaks the loop and can take down the entire network. All messages travel through a ring in the same direction effectively either "clockwise" each node passing on the data to the next node till it reaches its destination.

The following are examples of ring topologies:

• IBM Token Ring (although wired as a star)
• Fiber Distributed Data Interface (FDDI)

Advantages of Ring topology

• Growth of the system has minimal impact on performance
• All stations have equal access
• Each node on the ring acts as a repeater, allowing ring networks to span greater distances than other physical topologies.
• Because data travels in one direction high speeds of transmission of data are possible.
• When using a coaxial cable to create a ring network the service becomes much faster.

Disadvantages of Ring topology

• Often the most expensive topology
• Failure of one computer may impact others

Completely connected network: - The mesh topology connects all computers to each other. It is a way to route data, voice and instructions between nodes. A mesh network effectively extends a network by sharing access to higher cost network infrastructure. The cable requirements are high, but there are redundant paths built in.

Mesh topology has the following advantage:

• A mesh network is reliable and offers high speed.
• If one node can no longer operate, all the rest can still communicate with each other, directly or through one or more intermediate nodes.
• Mesh networks work well when the nodes are located at scattered points that do not lie near a common line.
• Easy to solve problems.

Disadvantages of mesh topology are as follows:

• The chief drawback of the mesh topology is expense, because of the large number of cables and connections required.
• Instillation and configuration system is very complex.

Bus topology: - In the bus network topology, every workstation is connected to a main cable called the bus. Therefore, in effect, each workstation is directly connected to every other workstation in the network. A single cable, the backbone functions as a shared communication medium, attaches or taps into with an interface connector with the devices.

Bus topology has the following advantage:

• Cabling costs are minimized because of the common trunk.
• Easy to implement.
• A relatively cheap and reliable topology.

Disadvantages of Bus topology

• Difficult to trouble shoot because no central distribution points exist.
• Limits on cable length and Workstation numbers.

Computer network

Computer Network: - 

In a communication system by which a computer is connected to another computer is called computer network. In other words a Network is set of technologies-including hardware, software and media that can be used to connect computers together, enabling them to communicate, exchange information, and share resources in real time.

Usefulness: - 

Network allows many users to access shared data and programs almost instantly. When data and programs are stored on a network and are shared, individual users can substantially reduce the need of programs on there own computer. Networks open up new ways to communicate, such as e-mail, instant messaging etc. By allowing users to share expensive hardware resources such as printers, networks reduce the cost of running an organization.   

Half duplex & full duplex

Difference between half duplex & full duplex are given below:-

·        Half duplex transfer data at a time in one direction; on the other handful duplex transfer data in both directions.

·        Half duplex requires less wire than full duplex system.

·        In full duplex transfer require less time than half duplex system.

·        Half duplex is less costly than full duplex mood.

·        Half duplex can not transfer data in both directions; on the other hand full duplex transfer data in both directions at a time.

RAM AND ROM

The difference between Ram and Rom are given below:

1. Ram stores data temporally and Rom stores data permanently.
2. Ram is volatile type; on the other hand Rom is non volatile type.
3. Ram holds data and program instruction while the CPU works with them; Rom holds data instruction that the computer needs to operate.
4. When a program launched it is loaded into and run from memory for faster access; When computers power turned on it checks ROM for direct instruction or direction that helps it start up and inform about it hardware device.
5. Rams data is always readable and rewritable; Rom’s data is non rewritable.

Optical Fiber

Optical Fiber: - Optical fibers are hire thin thread of glass or plastic, which can serve as a data transmission medium as copper wire or coaxial cables. The basic difference is that optical fiber transmits light signals instead of electrical signal. A fiber optic cable consists of three layers. The inner core is consisting of a cladding around it and outer protective coating.

Advantages: - The main components of optical fiber of an optical fiber in data communication system.

1. Large band with: - Optical fiber can transmit massive amount of data at very high speed and long distance.
2. High Speed: Because of light speed travels faster then electricity, optical fiber can transmit data at much higher speed.
3. Low loss: Light signal can travel, at very high with no significant loss over long distance.
4. Small size and light weight: Fiber optics is much smaller in size and lightens in weight.
5. Security: Optical fiber increase security since it extremely difficult and expensive to top optical signals.  

Application of Computer

Computer Application in our daily life:

Of present-day technology, computer use is very popular. Combined with the further development of the micro-computer, using the simplified operation, computer applications, are not limited to the application of scientific research and high precision. Sharing resources, communications, those two are the most original features of the first in their daily lives to be the most common applications. In ordinary everyday life, computer plays an increasingly important role. Almost every household has a computer. The extensive use of computers, convenient and well received by the people’s welcome.

Some common sectors of computer apps that we use our daily life are given below.

1) Home: Now a day’s computer is very available and in every home there is a computer. Generally in home we use computer Application for:-a) Communication,

                                                                                      b) Entertainment,

                                                                                      c) School life,

                                                                                      d) Small business.

Those are the common sector that we use computer application at home.

2) In Education: Computer apps have great use in education. There are no boundaries of use of computer application in education.

3) Business: We use computer apps in business for calculating, creating voucher, making design etc. Some common apps of computer that we use in business are MS WORD, Excel etc.

4) Medical Science: Computer apps have a great use in Medical Science.

5) Industry: In every big or small industry to accelerate productivity the use of computer apps is must.

In short, modern society, the rapid development of the network for computers the use of computer application is increasing day by day.

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