HARDWARE, SOFTWARE & USE OF COMPUTER

 

 HARDWARE AND SOFTWARE

• HARDWARE :- The physical component of a computer that we can touch, handle, or see physically is called Hardware. Hardware is tangible parts. Hardware is a computer, electronic and mechanical components. It consists all mechanical, magnetic, electrical or electronic devices like CPU, Disk, Disk Drive, Monitor, Keyboard, Mouse, RAM, ROM, Cable etc.
• SOFTWARE: - Software is a set of instruction that tells a computer what to do. Software is written computer program or a series of instructions. Software is program that allows the hardware to perform a useful work. Without software hardware is quite useless. Software interaction between user and computer. Software is needed to complete the input, processing, output, and storage and control activity of Information System. There are two type of Software.

System Software.

Application Software (Over view of software).

•  SYSTEM SOFTWARE :- 
  System Software is a group of program that controls all the operation of computer. It controls the use and distribution of various hardware components. This enables other application programs to execute properly. The system consists of programs that manage software and support the activities of a computer system and its information processing. System software is the type of software, which makes better & effective utilization of the entire computer system. It controls all operations of computer system. System Software serves as interface between systems, network, hardware and the application programs of end users. The manufactures provide it. The person preparing system software is called System Programmer & the process is called System Programming. The development of Compiler, Operating System, and High-Level Languages come under this category. For example, Operating System, utilities, device drivers & Network Management Programs.
•  APPLICATION SOFTWARE :- 
  Application Software is a type of software that is used to perform specific task for users. It is used to perform different task such as word processor, a spreadsheet of database etc. An application is the job or task a user wants the computer to do. Application software enables you to perform specific task, solve problem, and perform work. The person preparing application software is called application programmer. For example software developed for the PAYROLL of employees and program for maintain of personal record come under this category.
• General Purpose Software.
• Application Specific Software.

• GENERAL PURPOSE :- 
  General Purpose Program is application program that perform common job for end user. For example, word processing program, spreadsheet programs, database management programs (MS-Access, Oracle) and graphics program.
• SPECIFIC APPLICATION PROGRAM :- 
  Specific application program is used to support specific application. This type of software perform specific task. For example program for scientific analysis, engineering design & monitor of experiment. Computer application in education, entertainment, music, art, law & medicine etc.

 APPLICATION OR USES OF COMPUTER

1.     COMPUTER IN OFFICE: - Word processing or the use of computer as a typewriter is one of the most widely appreciated functions of the modern computer. The secretaries, newspaper reporters, intellectuals, novelist and writer who deal in words are no one found it useful. With a word processor, a user can type a report, a letter, a story, or whatever they want and view it on the computer screen. Modify, simple words in sentences, or paragraphs can be inserted or deleted or moved to different part of the document. Computer spell-check, and finally it is copied on paper using a printer.

2.     COMPUTER IN THE BANK :- Bank keep most of the record and data on computer. Bank accounts are maintained on the computer to avoid any chance of duplication or malfunction. The cheque is read by MICR (Magnetic Ink Character Readers) a device used to allow the data on cheque to be read by machine. Read the MICR at the bottom of each check, which is printed in magnetic ink, as well as special character numbers. Such computer is used to keep records of customer accounts, deposits, repayments, loans, interest etc.

3.     COMPUTER IN INDUSTRIES :- Computer is used to control manufacturing and producing systems and continuous running of the machinery. It is also helping to monitor the temperature and pressure measurements in the manufacturing process. Computers are used in the form of robots, in many industries

4.     COMPUTER IN EDUCATION :- Computer is used in schools in many different ways. They are used to help Montessori children learn different skills such as to distinguish between shapes, color etc. While college students use graphs and charts and computers can take advantage of the calculation of the mathematical and scientific assignments. The students use computer for Internet.

5.     COMPUTER SIMULATION FOR TRAINING :- Computer models can be used to train people such as pilots. A cockpit that is built on an airplane cockpit computer screen shows the picture of the model view, see the pilot, which look like using the computer.

6.     COMPUTER AIDED DESIGN :- Computer are used as a designing tool for engineers, architects and designer to perform their large, and complex job in a very short period. Examples of such a design project include car making, office building, and design plaza designing.

7.     COMPUTER IN HEALTH CARE :-Doctor diagnoses diseases by entering patient's symptoms in computer and prescribe medicines accordingly. The doctor takes the final decision but the computer speed up the process. It also keeps record of the patient's checkup and medicine etc.

8.     COMPUTER IN LAW :- In law chambers, computer is used to store a data bank of all those cases that have been already solved or decided. This helps her cope with the current situation that enables lawyers to study any case.

9.     COMPUTER IN POLICE DEPARTMENT :- The police department use the computer to help them catch criminals. About criminals and crime suspects data can be stored on the computer. A computer can find all the information about a crime, through which it can be fed into the database repository.

10. COMPUTER IN THE HOME :- Now a day the computer becomes a necessity of every home like other electrical appliances. Kids play games on it, stamp collection records, play pictures, play music, watch movies and try some kind of reading and writing according to needs. Parents can write their reports and mac calculations, mac budget etc. They can use computer for internet services and for electronic mail.

11. SCIENCE AND TECHNOLOGY :- All of us know that large computers can do millions of engineering calculation per second, can rapidly process the results of hundreds of Thousands of laboratory experiments in physics, and cars, is an important tool for modern designer most important microelectronic parts for aircraft and computers. Science and technology, computers not only for their skills in a number of useful but crunchier as simulation techniques. Exploitation of computer graphics simulation and model building model objects and worlds numerical skills. Space research in computer simulation is particularly useful. Computer simulation is also useful for weather forecasts predict earthquakes.

 

 

COMPONENT OF COMPUTER

 

BASIC COMPONENTS OF COMPUTER

There are three basic Functional Unit / Elements of a computer.

• Input Unit.
• Processing Unit.
• Output Unit.

Input Unit

The devices through which we enter data and instruction (Programs) into computer is called input devices. e.g. Keyboard, Mouse, Scanner, Digital Camera etc.

Central Processing Unit

Central processing unit (CPU) of a computer admin section. It is the brain of computer. CPU is located on motherboard. Data passes through CPU continually. Data come from RAM and other unit such as keyboard and drivers. The CPU processes the data and sends it back to RAM and other units. CPU all the input, output and storage devices connected to and controls all functions of these devices. CPU receives data from input devices perform data processing and output devices sends the result of the count data. The CPU is a combination of two units.

• Control Unit :- Control Unit is the nerve center of the computer. It controls all activities of computer system. The control unit direct and coordinate the entire Computer System in carrying out program instruction. It accepts data from input device and sends it to the memory. Memories data are then send the result to the output unit ALU.
• Arithmetic and Logic Unit (ALU) :- This is the calculation section Computer. All arithmetic operation like addition subtraction, multiplication, and division as well as some logical operation are performed in this section. It consists of two units a- Arithmetic Unit b- Logic Unit.
• Arithmetic Unit :- Arithmetic Unit of the ALU performs basic arithmetic function as addition such as addition, subtraction, multiplication and division.
• Logic Unit :- Logic Unit of the ALU performs logical operation like comparing two data items to find which data item is greater than, equal to or less than the other.

STORAGE UNIT (Primary Memory

The memory is stored in the processing space where computer programs and data. It is a temporary storage unit for memory information, instructions and information. The storage unit is often called main storage or internal storage or primary storage. Usually there are two types of primary storage.

• RAM :- 
  It stands for Random Access Memory or read / write Memory because information can either be read from or written to RAM. RAM is called volatile or semiconductor memory. This is the memory whose or semiconductor memory. It is memory which can be erased or changed. It is temporary memory. Anything stored in RAM is lost when Computer is switched off.
• ROM :- 
  It stands for Read Only Memory. Information ROM can be read but can not write the information. It is memory that cannot be changed information. If we turn off the computer, the information stored in it cannot be lost. ROM is used to store permanent program. This informatics’ available on small pieces of the memory called chips. If we turn off the computer, the information stored in it cannot be lost.

OUTPUT UNIT

The user is called production unit output device used to display information. An output device can be used to store, display or print the information. e.g. monitor, printer, speaker etc.

 INPUT AND OUTPUT DEVICE

Input Device :-
We called the device through which data and instructions in a computer input device. There are many devices for input. These devices of a digital Computer are responsible for accepting programs and data from the outside world, feeding it to the computer memory. These devices work in micro-processor control. Below are some of the popular input devices, keyboard, mouse scanner, microphone, video camera, touch screen, and optical scanning.

Key Board :- 

This key is a very common input tool that helps in the necessary information in the computer. The keyboard can be used effectively to communicate with the computer input device, but it is very slow. The keyboard is just like a typewriter in shape but enhance than that. It consists of normal Alphabetic, numeric, functions & other special characters or control keys, which are not available in a typewriter.

1.     Pointing Devices :- 
Used to control a pointer on the screen is called using an input device indicating devices. A pointer is a small icon that appears on the screen in the graphical user interface. Some example of pointing devices is Mouse. Track ball, joy stick etc.

o    MOUSE :- 
A mouse is a quick input device and is very small in size. The mouse is moved on a flat surface to control the movement of a cursor on a screen (pointer). A mouse usually has two buttons & one scroll ball. These buttons are used to perform various functions.

o    THE TRACKBALL :- 
The track ball is often used in place the mouse pointing devices. A trackball (inverted) device related to the mouse. It's a ball over and you can spin with your hand directly to the ball. The trackball is used in laptop computer. No need of mouse pad for track ball.

2.      TOUCH SENSITIVE SCREENS :- 
Touch screen finger touch is a video display screen that get their input. The screen is covered with a layer of plastic. Behind the scenes there are invisible beam of infrared light. The user enters data by touching icons. or menus on the screen. Most touch screen computer use sensors to detect a finger touch.

3.     PEN - BASED COMPUTING (LIGHT PEN) :- 
Do not enter data into the computer via a video screen pen-based devices use the optical circuit. A user on a display, light-sensitive pen can write the user sends specially designed pen touch screen parts information to the computer. Light pens are commonly used by engineers, graphic designers, and illustrators.

4.     VOICE RECOGNITION :- 
The voice recognition device is used to convert spoken data directly into electronic from a computer system. Voice recognition and voice response is the easiest way for data entry and conversational. The microphone is connected to the computer with voice support. The capability of a computer to distinguish spoken works is called voice recognition or speech recognition. Voice input is a fast way of entering data. Much word processing application. Provide the facility of voice input. The user speaks in microphone and the application software writes the spoken words as a text. Speech microprocessors toys, calculators, tools, automobiles, and other users can find, commercial, and industrial product type. 

5.     SCANNER :- 
Scanner is Optical character recognition equipment that can read special - purpose characters and codes. The scanner provides a way to insert data directly from source documents into a computer system. There are many types of optical readers, but they all use photoelectric devices to scan the readable characters. Data light patterns electronic impulses, which are then reflect the change to be accepted as input into the computer system. OCR-based optical scanning systems are widely used in credit card billing operations of credit card companies, banks and oil companies.

6.     MICROPHONE :- 
This is an input device that is used for keyboard and voice input instead of using the mouse. Special software place of using the keyboard and mouse. Special software is used to convert voice into test. This fast processing and a lot of memory and will become more common as technology improved. The microphone converts the digital audio signal

7.     VIDEO CAMERAS :- 
The video camera is an input device that is capable of capturing any kind of data images. Most scanners incorporate a special type of camera that is made up of a charge-coupled device (CCD). Each CCD receives light from the image and the light generates an electric charge. This means that the image dots represent light areas and dark areas of the charged cells of the non-charged cells.

8.     DIGITAL CAMERA :- Digital Camera is used to take and store picture in digital form. It does not use traditional camera film. It save money and the photos can be customizing using different application software. Digital cameras store pictures using different techniques like floppy disks. Super disk, PC card. Compact flash card, memory stick and micro drive. Through the digital camera's USB port can be easily connected to a computer.

OUTPUT DEVICES

Device information is a process by which output devices to the outside world. To print to an output device or information can be used. (e.g. monitor, printer, plotter, speaker).

MONITOR:-
A TV like device that is used by the Computer for displaying the information to the outside sued is known as CRT or VDU or more simply a Computer Screen. The monitor is basically glass cone, the cone back and which contains special electron guns to hit the screen with different colors to create text or graph. Monitors / Screens can be selected on the basis of user requirements. The following are the different types of monitors.

 

 

MONOCHROME MONITOR:-
Monochrome means one color. Monochrome displays images in a single color, usually white or blue display. Normally Monochrome is any monitor that cannot display colors. They can be black and white type but they are often available in green colors because green color is easier to eyes. A Monochrome monitor usually cannot display graphics. But then monitors the technique was developed to have graphics capability.

COLOR MONITOR:-
Color monitor display output in different color. Graphics, picture4 and colorful images are best viewed in colorful images are best viewed in color monitor. 

FLAT PANEL OR LCD MONITORS :-
Laptop PCs use flat-panel monitors. These monitors take less space. Use a variety of flat panel monitor technology. The most common is LCD (Liquid Crystal Display), LCD monitor use much less power than manual monitor. The LCD monitor is generally transparent but produces images with a special type of liquid crystal that becomes solid when charged electrically.

PRINTERS :-
Role of printer paper, logos, and graphics output device that prints. Hard copy is the printed output. Generally inch print resolution (DPI) is measured in dots per. Many types of printers vary in speed and quality. Different types of printers as follow

1.     Impact Printers.

2.     Non-Impact Printers. 

IMPACT PRINTER :-
Impact printer works like a typewriter. It can kill a print hammer or wheel against an inked ribbon or images in print. Impact printers are the following

• DOT-MATRIX PRINTER :- Dot Matrix printer produce prenticed images when tiny pins on a print head strikes an inked ribbon. Press the ribbon against the paper, it creates dots that form characters and graphics. The dot matrix printer head contain 9 to 24 pins. It depends on the printer model number and manufacture of pins. A number of pins that have more dots print high-quality output. 150 DPI affordable dot matrix printer uses 100. His speed is 200 to 300 characters per minute. 300 DPI printers are expensive and speed from 1000 to 3000 characters per minute.
• DAISY-WHEEL PRINTERS :- Daisy wheel is similar to type writer. As dot matrix printer rather than create excellent letter quality printout. They work just like a typewriter and using a hammer and a wheel to print anything on paper. But they are very noisy and therefore are not so popular. Impact Printers other so-called non-impact printers.

NON-IMPACT PRINTER

Non-Impact Printer Paper produces character without striking devices. They are much quieter than impact printer. The following are the non-impact printer.

• LASER PRINTERS :-  The most expensive and quality bearer printers are the laser printers, which produce high quality printout and are used for desktop publishing and graphics. A laser printer works on the principles of a photocopy. Only the toner is loaded with a special metal drum, and thus the printed ink splashed on paper only. They use multiple fonts for text and graphics as well as fast in work. Apart from these there are now color printers available in dot matrix as well as laser printers and all the others as well.
• INK JET :- It prints character and graphics by spraying tiny drops of liquid in on paper. It can create both text and graphics in black and white and color printers. Inkjet printer is slower than laser printer. They can print from 1 to 6 pages per minute. The higher print quality dot matrix printer. And the use of a black ink Color: Most inkjet printers usually have two print cartridges.

PLOTTERS
In a variety of color plotter is an output device that is used to create photo-quality graphics. Plotter works by drawing lines on paper using a mechanical arm holding pen. They are mostly used for engineering drawings and Maps purposes.

SPEAKER 7 HEADSET
The speaker is an output device for producing audio. These devices are music, speech, or beep speaker and headset etc. The two commonly used audio output devices such as a second voice. It produces soft copy output. We use the speaker to listen to any sound.

STORAGE DEVICE
The device in which we store the data and information is called storage devices. there are two types of storage device.

• Main / Primary Storage Devices.
  Rom
• Secondary Storage Devices.
  Hard Disk, Floppy Disk, Flash Drive, USB etc.

Main / Primary Memory or Internal Memory :-

The Main memory (Primary Memory) of CPU is they place where the computer program and data are stored during processing. This storage unit is often called either central storage or internal storage or primary storage.

• RAM :- It stands for Random Access Memory or write/read memory because information can either be read from or written to the RAM. It is memory which can be erased or changed. It is temporary memory. Stored in RAM is lost when the computer is off anything.
• ROM :- It stands for Read Only Memory. Information can be read from ROM but we cannot write or change information  to it. It is memory that cannot be changed information. We cannot lose the information stored in the computer, then turn off. ROM is used to store permanent program. This information is available on small pieces of memory chips called.

Secondary / Auxiliary / External Memory (Storage)  :-

A computer device such as software and data store information that is permanently called secondary storage. Disk can store a large amount of data can be obtained and where it is, where it is a secondary storage device. It has different types e.g. H.DD., CD-ROM, Removable Disk, Magnetic Tape etc.
Following are the Secondary Storage Devices:

• Magnetic Disk:- 
  The Magnetic Disk is made up of one or more rotating platters, on which data is stored magnetically. It is made from coated on both sides with a magnetic object that iron oxide plastic. We have two main types of Magnetic Disk, which is used in computer, i.e. Floppy Disk and Hard Disk.
• Hard Disk:- 
  It made up of one or more rotating platter, which is enclosed with magnetically object that is iron oxide. This circular object that metallic ally iron oxide. It is a circular metal plate is completely sealed off as relatively thick in size and permanently. Date is recorded on magnetic plates. 
• Floppy Disk: - 
  It is a removable Plastic Disk. It is not fixed in the computer. The object of the magnetically encoded with the iron oxide. Hard disk storage capacity is less. You must have a floppy disk drive to use a floppy disk. You must have a floppy disk drive to use a floppy disk. Floppy disk drives are used for A & B.

•  OPTICAL DISK STORAGE :- 
  Optical Disk is the fast growing storage medium. CD-ROM is Optical disk. Compact Disk Read Only Memory is known as CD-ROM. CD-ROM technology uses 12 centimetre (4.7 Inches) compact disk similar to those used in stereo music system. It is the latest invention. It is so called CED-ROM because the information may be just read from it but not written down. A CD-ROM can store up to 840 megabytes of data. We run CD through CD Rom. You must use the CD-ROM to a CD. Other optical disk technology produces WORM (Write Once Read Many) and CD-R (CD Record able) disk. CD-ROM, CD-R, and the worm drive is important that the recorded data cannot be erased. However erasable optical disk system is also available (CD-RW). CD-RW provides full re-writable capabilities. This technology record and erases data by using a laser to heat a microscopic point of the disk surface. In some version, a magnetic coil changes the spot reflective property from one direction to another, thus recording a binary one or zero (1 or 0), a laser device can then read the binary code on the disk by sensing the direction of reflected light. The newest optical disk is digital video disk (DVD) or digital versatile disk provide to large amount of data and transferring data on higher speed (up to 12MBps). Digital Video Disks are designed to work with a video player and television.
• MAGNETIC TAPE: - 
  Magnetic Tape is a flexible plastic tape, coated on one side with magnetic iron oxide material. It is used when large amounts of data are to be processed sequentially. An advantage of magnetic tape is that is very cheap and economical storage medium but very slow in processing.
•  MAGNETIC DRUM: - 
  It is therefore a rotatable cylinder whose surface is coated with a magnetically sensitive iron oxide compound. A number of the tracks, each track is divided into one or more of the reading and recording heads it. Magnetic drums are commonly used when very fast access and transfer speeds are required. There is one disadvantage is that they cannot be removed from the unit.
• FLASH MEMORY: - 
  Now a day the latest and modem storage device is flash memory or USB is used as a secondary storage device. It is semiconductor memory. This RAM is the same as ROM in circuitry. It is used as secondary storage for moving data.

NETWORKS AND INTERNET

 

Introduction

To manage network security, you will need knowledge of how computer networks operate. Those readers who already have a strong working knowledge of network operation may choose to skim or perhaps give it a quick read as review. For others new to computer networking, study will give you a basic introduction to how networks and the internet work. This understanding of networks and internet will be crucial to your comprehension of later topics presented.

We will try to understand that how will examine the basic model of network and the underlying technologies that allow networks to communicate. This information will be the foundation on which all of the other materials in this course are build. You will be able to practice using some utilities i.e. IPCongfig, tracery, & ping.

The OSL Model

Let’s begin with the OSI model or open system interconnect model. This model is a description of  how networks communicate. It describes the various protocols, activities and it delineates how the protocols and activities related to each other. This model is divided into seven layers which is shown in following. It was original developed by the International Standards Organization (ISO).

Layer	Description	Protocols
Application	This layer interfaces directly to the application and performs common application services for the application processes.	Non
Presentation	The presentation layer relieve the application layer of concern regarding syntactical differences in data representation within the end-user system	POP, SMTP, DNS, FTP, Telnet, ARP
Session	The session layer provides the3 mechanism for managing the dialogue between end-user application processes	NetBIOS
Transport	This layer provides end-to-end communication control	TCP
Network	This layer routes the information in the network	IP, ICMP
Data Link	This layer describes the logical organization of data bits transmitted on a particular medium. Data Link is divided into two sub-layers: the Media Access Control layer (MAC) and Logical Link Control layer (LLC)	SLIP, PPP
Physical	This layer describes the physical properties of the various communications media, as well as the electrical properties and interpretation of the exchanged signals. In other words, the physical layer is the actual NIC, Ethernet Cable and so forth.	None

 

Many networking students memorize this mode. It is good to at least memorize the name of the seven layers and in general understand what they each do. Form a security perspective, the more you understand about network communications, the more sophisticated your defense can be. The most important thing for you to understand is that it describes a hierarchical model of communication. A layer will interact directly with the layer above or below it.

Network Basics

Getting two or more computers and a process to transfer data that is simple in concept but complex in. Consider all the factors involved. First, you'll need to physically connect to the computer. This connection is accomplished by either your computer or plug in a cable to infrared light. The cable is then plugged either directly into another computer or is plugged into a router which ort a hub that will, in turn, connect to several other computers.

Most modern computers have a card called a network interface card or a NIC. The connection is via a cable, so the computer has a connection slot that looks like a telephone jack, just a little bigger that looks part of the NIC that is external. Of course wireless network, which is a slot for a cable to connect to, the wireless network simply uses infrared signals to transmit to a nearby wireless router or hub.

Media Access Control (MAC) Addresses

MAC addresses are an interesting topic. (The data link layer of the OSI model of Mac you can feel Layer). A MAC  address is a unique address for a NIC. Every NIC in the world has a unique address represented by a six byte hexadecimal number. MAC addresses is a protocol that is used to change the IP addresses. This protocol is the Address Resolution Protocol or ARP. Therefore, when you type in a Web address, the DNS (Domain Name Server) protocol is used to translate that into a IP address. The ARP protocol will then translate that IP address into a specific MAC address of an individual NIC.

DNS Servers

How does a URL get translated into a IP address? IP is the URL that the computer how to do? Servers have been set up to perform this task. There are only set up servers to do the job. DNS stands for Domain Name Server (or System or Service). DNS translates domain names (www.example.com) into IP address (199.246.58.4). To remember domain names are alphabetic, because they are easy, but the Internet is really based on IP addresses. Thus, every time you use a domain name, a DNS server must translate the name into the corresponding IP address. If you are on corporate network, you probably have a DNS server on your network. If not, those, you ISP have one. These servers maintain a table of IP-to URL entries.

From time to time there are transfers of DNS data, called zone transfers, that allow one DNS server to send its changes to another. Across the Internet, there are root DNS server that are maintained with centralized data for all registered URL/IP addresses. The DNS system is, in fact, its own network. If one DNS server does not know how to translate a particular domain name, it asks another one and so on until the correct IP address is returned.

Primary DNS is the name given to the server or service that holds the authoritative information for a domain. Actually, a DNS server ( the computer / software) is not specifically “primary” or “Secondary”. A DNS server can be primary for one zone (domain) and secondary for another. By definition, a primary DNS server hold the master copy of the data for a zone and secondary servers have copies of this data that they synchronize with the primary server through zone transfers at intervals or when prompted by the primary server.

The physical connection: Local Network

Cable is a way through which more than one computes connected. The cable connection used with hard-wired NICs us an RJ-45 connection. (RJ is short for “Registered Jack”, which is an international industry standard). In contrast to the computer’s RJ 45 jacks, standard telephonic lines use RJ 11 jacks. The biggest different between jack involves the number of wires in the connector, also called the terminator. Phone lines have four wires, whereas RJ 45 connectors has eight.

If you look on the back side of computers or laptop, you will mostly find three ports that, at first glance, look as phone jacks two of the three ports are probably for a traditional modern and telephone and accept a standard RJ-11 jack.  One port is used for RJ 45 connector. Not all computers come with a NIC, most modern computer do. Additionally, many modern computers no longer contain an internal modern, in which case there would not be an RJ 11 jack.

This standard connector jack must be crimped on the end of the cable. The cable used in most networks today is a category 5 cables – or CAT 5, as it is commonly known. (Not that CAT-6 cable is becoming more prevalent with high – speed networks). 

 

Category	Specifications	Uses
1	Low-speed analog (less than 1 MHz)	Telephone, doorbell
2	Analog line (less than 10 MHz)	Telephone
3	Up to 16 MHz or 10 MBps (megabits per second)	Voice transmissions
4	Up to 20 MHz / 16 MBps	Data lines, Ethernet networks
5	100 MHz / 100 MBps	Most common types network cable
6	250 MHz / 1000 MBps	Very high-speed networks

 

The type of cable used in connecting computers is also often referred to as shielded twisted pair cable (UTP). In UTP, the wires in the cable are in pairs, twist together without any additional shielding. As you can see in above mentioned table, each subsequent category of cable is somewhat faster and more robust than the last. It should be noted that, although CAT-4 can be used for networks, it is most never used for that purpose simply because it is slower, less reliable and oldest technology. You will usually see CAT – 5 cables and it is also increase upto CAT – 6.

Notice the speeds listed in table, such as MBps. This speed stands for megabits per second. Ultimately, everything in computer is stored in binary format using a 1 or 0. These units are called bits. It takes eight bits, or one byte, to represent a single character such as a letter, number or carriage return. It follows, then, that CAT – 5 cable can transmit up to 100,000,000 bits per second. This is known as the bandwidth of the cable. Remember, though, that this is the maximum that can be transmitted “across the wire” at any given second. If multiple users are on a network and all of them are sending data, the traffic generated is going to quickly use up all of the bandwidth. Simple scanned-in photos can easily reach two megabytes or much more. Steaming media, such as video is perhaps the most demanding on bandwidth.

If you simply want to connect two computers to each other, you can have the cable go directly from one computer to the other. But what do you do if you wish to connect more than one computer? What if 100 computers need to be connected on a network? There are three devices that can help you accomplish this task: the hub, the switch, and the router. These devices each use CAT – 5 or CAT – 6 cable with RJ – 45 connectors. 

1.      The Hub
the simplest connection device is the HUB. A hub is a small, box-shaped electronic device into which you can plug network cable. It will have four or more (typically 24) RJ 45 jack him, met each port. This is as a center as many ports can connect to the computer. You can also connect on hub to another; this strategy is referred to as “stacking” hub. Very cheap and easy plug-in cable to connect --- centers. However, however, hubs have a downside. If you send a packet from one computer to another, a copy of that packet is actually send out from every port on the hub. All of these copies lead to a great deal of unnecessary network traffic. There is no way of knowing where the center, because it is a very simple device occurs, a packet should be. Therefore, it simply sends copies of the packet out of all of its ports.

2.      The Switch
The next connection device option is known as Switch. A switch is basically an intelligent hub. However, a switch receive a packet, it will send that packet only out the port for the computer to which it needs to go. A switch builds a table based on MAC addresses and uses that to determine where a packet is being sent. How this determination is made is explained in the Data Transmission section below.

3.      The Router
Finally, if you want to connect two or more networks together, you use a router. A router is similar in concept to a hub or switch, as it does relay packets; yet, it is far more sophisticated. You can program most routers and control how they relay pockets. How your router vendor programs such details are different form. However, you should be aware that most routers are programmable, allowing you to change how they route traffic. Moreover, unlike using a hub or switch, a router connected to two networks are still separate networks. In short, the three basic connection devices are the hub, switch and router all of which connect category 5 or category 6 cable using RJ 45 connectors.