BUS SYSTEM IN A MULTIPROCESSOR SYSTEM

A number of bus configuration are available for a multiprocessor system.Example are:single shared bus system,dual bus system,crossbar interconnection,hypercube system,etc. A few bus system are described below in brief.
Fig 1 shows a single shared bus architecture.In such a system one processor is allowed to communicate with the memory or another processor at any given time.since it is restricted to one transfer at a time,its data transfer rate within the system is limited by the speed of the single sheared us system.It has been used in computer system because it can easily be designed and controlled.

fig1: single-Bus System

Fig 2 shows a dual bus configuration.In this system local buses are employed.Each local bus is connected to a CPU,the local memory and I/O.A system bus controller connects each local bus to a common system bus.The memory and I/O connected to the common bus can be sheared by all processors.In this system only one CPU is allowed to communicate with the shared memory and other common resources through the system bus at any given time.The other processors use their local memory and I/O devices.It is an improvement over the single shared bus system.It has higher data transfer rate.But is a costly and complex bus system.

Phasor diagram of real transformer

Phasor diagram for the exact equivalent circuit of real transformer

Types of electrical switches

• SPST(single pole single throw)
• SPDT(single pole double throw)
• DPST(double pole,single throw)
• DPDT(double pole,double throw)

SPST(single pole single throw):The spst is a basic ON/OFF switch,that is used to connect or break the connection between two terminals.This type of switch has one i/p and one o/p.This type of switch circuit controls one wire and make one connection.

SPDT(single pole double Throw):The SPDT switch is a three terminal switch,one terminal is used as i/p and remaining two terminals are used as outputs.

DPST(double pole,single throw):The DPST switch consists of two poles that means it includes two identical switches located on side by side.This switch is operated by one single toggle,which means that two discrete circuits are controlled at a time through one push.

This switch is used to turn two circuits ON/OFF and it consists of four terminals namely two inputs and two o/ps.

DPDT (double pole double throw):This switch is equal to two SPDT switches,it means two separate circuits,connecting two inputs of each circuit to one of two o/ps.

when it is in ON-ON mode or ON-OFF-ON mode they work like two discrete SPDT switches worked by the similar actuator.

PLOTTERS

plotters are output devices.They are used to produce precise and good quality graphics and drawing under computer's control.They use ink pen or ink-jet to draw graphics or drawings.Either single color or multicolours  pens can be employed.The pens are driven by motor.Drawing can be prepared on paper,vellum or mylar (polyster film). colour transparency can also be prepared.
Pen plotters are slow devices.The graphics and drawing produced by pen plotters are uniform and precise,and they are of very good quality. they are used for low to medium volume job. A pen plotter can make from several seconds (for simple drawing) to several minutes (for complex drawings) to produce a drawing. ut it takes much  less time as compared to traditional hand methods  of producing drawings . A complex drawing which can take about a month by traditional hand method can be produced in less than an hour using plotters.

 the pen plotter may be classified into the following types:               

 Drum plotters:
A drum plotter contains a large cylinder and a pen carriage . the  paper is placed over the drum (i.e. cylinder). The drum rotates back and forth to give up and down movement . The pen is mounted horizontally on the carriage. The pen  moves along with the carriage left  to right or right to left on the paper to produce drawings . Under the computer control both the drum and the pen move to produce the desired drawings. Several pens with ink of different colours can be mounted on the carriage for multicolour drawings. Since each pen is program selectable, a multicoloured drawing can be produced.

Microgrip plotter:
 Such plotter don't use drums. The paper or any other medium is held(gripped) on both sides at the age y pinch wheels which give back and forth paper movement. With such plotters high performance is attained at a low cost.

Flat-Bed plotters:
Some  plotters employ ink-jets in place of ink pens. The paper is placed on a drum and the ink-jets with different-coloured ink are mounted on a carriage. Such plotters are capable of producing multicolour large drawings.   

USE OF COMPUTER IN COMMUNICATION

Computers are extensively used in sending and receiving information.The information transfer may take place either between two points or throughout a computer network that connects a number of computers or workstations.Data communication packages are available which are used to send and receive information.For communication purpose one must have a computer,a data communication package and a modem.Usually,telephones lines are used over which data are transmitted from one place to another.

The telephones lines are used over which data are transmitted from one place to another.The telephone lines have been built for voice transmission.To transmit human voice continuously variable analog wave patterns are used.Thus a telephone line is designed to transmit analog signals.on the other hand,a computer processes digital signal consisting of pulse or no pulse,i.e presence or absence of an electrical voltage.Digital signals can not be transmitted over existing telephone lines which have been designed to transmit analog signals.Hence,modems are needed to convert or modulate digital signals to analog signals and vice versa when exiting telephone lines are to be used.A modem connects a computer to the telephone lines.The modem receives data from a computer or a terminal which are to be transmitted over telephone lines.The modem converts(modulated) the digital signals into analog signals which can be transmitted over the telephone lines.The modem at the other end receives the data from telephone lines and converts (or demodulates) the received analog signals into digital signals.These digital signals are processed by a computer at the receiving end and they are reproduced as the original information.Data can be transmitted in both directions.A modem performs both tasks:modulation and demodulation.when data is being transmitted from an end,the modem placed at that end performs modulation.when data is received at an end the modem placed at this end performs demodulation.

                                                                                     

Arrays Vs Structures

Both the arrays and structure are classified as structured data types as they provide a mechanism that enable us to access and manipulate data in a relatively easy manner.But they differ in a number of ways.

1.An array is a collection of related data elements of same type.Structure can have elements of different types.

2.An Array is derived data type whereas a structure is a programmer-defined one.

3.Any array behaves like a built-in data type.All we have to do is to declare an array variable and use it.But in the case of a structure,first we have to design and declare a data structure before the variables of that type are declared and used.

Arrays

An array is a fixed-size sequenced collection of  elements of the same data type.It is simply a grouping of like-type data.In its simplest form,an array can be used to represent a list of numbers,or a list of names.

an array is a sequence collection of related data items that shear a common name.For instance,we can refer to the individual salaries of a group of employees in an organization.we can refer to the individual salaries by writing a number called index or subscript in brackets after the array name.For example,represents the salary of the 10th employee.while the complete set of values is referred to as an array,individual values are called elements.

The ability to use a single name to represent a collection of items and to refer to an item by specifying the item number enable us to develop concise and efficient programs.

we can use arrays to represent not only simple lists of values but also tables of data in two or three or more dimensions.the following types of arrays.

• One-dimensional arrays
• Two-dimensional arrays 
• Multidimensional arrays