Computer Science UGC Net

HUB Hub is a controller that controls the traffic on the network.  The following important properties of hub are:  1) It amplify signals. 2) It propagates signals through the network. 3) It does not require filtering. 4) It does not require path determination for switching. 5) It is used as network concentration points. Hubs are basically two types: 1) Active hub 2) Passive hub Active hub: A ctive hub works as repeater which is a hardware device that regenerates the received bit pattern before sending them out . Passive hub : A passive hub is a simple hardware device which provide a simple physical connection between the attached devices. Advantages of hub: It cannot filter the traffic full stop feeling generally refers to a process or device that screens network traffic for certain characteristics such as source address and destination address and protocol. Disadvantages of hub: On a hub, more than one user may try to send data on the network at sam

Network Topology The arrangement in which elements like links, nodes of common network are connected is known as network topology. Example of Network topology is found in local area network. We have five types of topologies : 1.) Mesh Topology 2.) Bus Topology 3.) Ring Topology 4.) Star Topology 5.) Hybrid Topology 1.) Mesh Topology : In mesh topology every device is connected with another device via a particular channel. 2.) Bus Topology : The bus topology is used when a network installation is small, simple and temporary. On a typical bus network cable is just one or more wires with no active electronics to amplify the signal or pass it along from computer to computer. This makes the bus a passive topology. Only one computer can send data at one time therefore the number of computers attached to a bus network can significantly affect the speed of the network a computer must wait until the bus is free before it can transmitted. Advantages of bus topology: E

Normalization : Normalization is the process of transformation of the conceptual schema of the database into a computer represent table form. Normalization is the process of removing the redundancies from incoming data.  Normalization is a technique to which helps the user to group the data and place the data in a table.  Normalization is a process which ensure the inconsistencies are not introduced into the database. Need of Normalization : we know with the time, most of databases grow time to time by adding new relations and relationships, the data may be used in different ways. Regularly the information may undergo series of updations in such situations, the performance of a database is entirely dependent upon its design.      A bad  database design  may lead to certain undesirable things: Repetition of information Inability to represent certain information  Loss of information Uses of Normalization: When data is large and scattered There is no defined group

Generalisation is an abstraction for sharing similarities among classes while preserving their differences. For example, each piece of equipment has a manufacturer weight and cost . Pumps also have suction pressure and flow rate. Tank also have volume and pressure we would like to define equipment features just once and then add details for pump, tank and other equipment types. Generalisation is a relationship between a class and one or more refined versions of it. The class being refined is called superclass and each refined version is called a subclass. For example equipment is the superclass of pump and tank. Attributes and operations common to a group of subclasses are attached to the superclass and shared by each subclass. Each subclass is set to inherit the feature of its superclass, for example, pump inherites attributes manufacturer, weight and cost from equipment. Generalisation is sometimes called the "is-a" relationship because each instance of a subclass is

Preemptive Scheduling : In contrast to non preemptive scheduling, a scheduling decision can be made even while the job is executing whereas in non preemptive scheduling, a scheduling decision is made only after job completes its execution. Therefor preemptive scheduling may force a job in execution to release the processor, so that the execution of some other job can be undertaken, in order to improve throughput considerably. Types of preemptive scheduling: 1) Round Robin scheduling algorithm : the round Robin scheduling is designed for time sharing systems. The primary objective of round Robin scheduling are interactive use, good response time and sharing the resources equitable among processes. It is similar to FCFS, but preemption is added to switch between processes. The processes are alocated a small unit of time. Known as time Quantum or time slice is in rotation until the completion of processes. To implement round Robin scheduling, a FIFO(first in first out) queue

Scheduling : In multi-programmed computer, multiple processes competing for the CPU at the same time. This situation occurs whenever two or more processes are simultaneously in the ready state. If only one CPU is available. Then we need a system that decide which process run first and then next and this will be done by the scheduler. Scheduler : scheduler is an operating system module that she loves an axe top to be admitted into the system and then the next process to run. Scheduling is of two type: 1) Pre-emptive 2) Non pre-emptive Non Pre-emptive Scheduling : In batch non Pre-emptive scheduling implies that, once scheduled, selected job runs to completion. In other words, the running process not forced to relinquish ownership of the processor when a higher priority process becomes ready for execution. The scheduling techniques which use non preemptive scheduling are: 1) first come first serve (FCFS) scheduling 2) shortest job next (SJN) scheduling 3) dea