Data Transmission Mode

The way in which data is transmitted from one place to another is called data transmission mode.

Types of Transmission Modes

There are three types of data transmission modes:
1.Simplex Mode

In simplex mode, data can flow only in one direction . It cannot  be moved in both directions. It operates in a manner similar to a one-way street.The direction of flow never changes.A device with simplex mode can either send or receive data. It cannot perform both actions. An example is a traditional television broadcast. The  signal is sent from the transmitter to TV antenna. There is no return signal.

 2. Half - Duplex Traffic:

In half - duplex mode , data can flow in both directions but not at the same time. It is transmitted one - way at one time. A device with half- duplex mode can send or receive data but not at the same time.That is why the speed of half-duplex mode is slow.An example of half-duplex is a narrow bridge that can carry single vehicle at a time .The traffic from side A stops while the vehicles from side B cross the bridge. Similarly, traffic from side B has to stop so that the Vehicle from side A may cross.

3. Full-Duplex Mode

In full- duplex mode, data can travel in both directions simultaneously. Full duplex mode is a faster way of data transmission as compared to half duplex. Time is not wasted in changing  the direction of data flow. A telephone is a full- duplex device . Both persons can talk at the same time.Another example of full- duplex communication is automobile traffic on a two- lane road.The traffic can move in both directions at the samwe time.

Network Topologies

A network can be configured or arranged in different ways. The physical layout or arrangement of connected devices in a network is called topology. It is the shape of a network . Different network topologies are as follows:

• Bus Topology

Bus topology is the simplest type of network.It supports a small number of computers. In bus topology, all computers or network nodes are connected to a common communication medium.This medium is often a central wire known as bus. The terminators are used at the end of a bus to absorb signals.A collision can occur in bus topology if two computers transmit data at same time .Bus topology is mostly used in peer-to- peer networks.

• Working of Bus Network 

 

The sending computer sends the data and destination address through the bus. The data and address move from one computer to the other in the network. Each computer checks the address. If it matches with the address of a computer, the computer keeps the data.Otherwise the data moves to the next computer.
Advantages 

1. It is simple and easy to use.
2. It requires small length of  cable to connect computers. 
3. It is less expensive.
4. It is easy to extend a bus . It allows more computers to join network. 
5. If one node fails, it does not affect the rest of the network.

 Disadvantages 

1. It is difficult to troubleshoot . 
2. It only supports small number of computers.
3. The network speed slows down as the number of computers increases.

 Star Topology

All computers in star topology are connected with central device called hub, star topology is mostly used in client- server networks. 

Working of Star Network

The sending computer sends the data to hub.The hub sends data to the receiving computer. Each computer in star network communicates with a central hub.

Advantages

1. It is easy to maintain and modify network.
2. Adding or  removing computers can be done without disturbing the network.
3.  Finding faults becomes very simple.
4. Single computer failure does not bring down the  whole network.
5. It is more flexible than other topologies.
   

Disadvantages:

1. It central hub fails, the entire network breaks down
2. It requires a large length of cable to connect computers.
3. It is more expensive.

Rind Topology

In ring topology, each computer is connected to the next computer with the last one connected to the first. Thus a ring of computers is formed.

Working of Ring Network

Every computer is connected to next computer in a ring . Each computer  receives message from the previous computer and transmits it to the next computer. The message flows in one direction. The message is passed around the ring until it reaches the correct destination computer.


Advantages

1. It is less expensive than star topology.
2. Every computer has equal access to the network.

Disadvantages

1. Failure of one computer in the ring can affect the whole network. 
2. It is difficult to troubleshoot.
3. Adding or removing computers affect the whole network.

Communication Devices

 The hardware used to transmit data, instructions and information between a sending and  receiving device is called communication device. A communication device at sending end sends data to a communication channel. A communication device at receiving end receives data from communication channel. Some communication devices are as follows: 

Modem

Modem stands for modulation and demodulation. Modem is a device that converts digital signal into analog  and analog signal into digital. Modem sends and receives data from one computer to another  through telephone lines. The sending and receiving computers both must have modems. A process of converting digital signal is called modulation. Computer stores data using telephone line, so it is converted from digital to analog form. A process of converting analog signal into digital signal is called demodulation. The modem on receiving computer receives data in analog form and converts it into digital format to be used by the computer.

Network Interface Card

Network Interface Card (NIC) is also called LAN adapter. It is used to connect a devices to a network. The transfer rate of an Ethernet card is from 10 Mbps to 1000 Mbps to 1000 Mbps. Different NIC are available for different types of computers. Network cards for wireless data transmission are also available. These adapter cards often have an antena.

Wireless Access Point

 A wireless access point is a central communication device. It allows computer and other devices to transfer data wirelessly among themselves or to a wired network.Wirless access points have high quality antennas for optimal signals. Some manufactures suggest to place the wirless access point at the highest possible location for the best signal.




Routers
A router is a communication device that connects multiple computer or other routers together. It connects multiple networks using similar or different protocols. It manages the best route between any two communication networks. Routers are used when several networks are connected together. They can connect networks of different countries. They transfer data in less time. The router is an intelligent device. It uses algorithms to find out the best path to transfer data to network.

HUB

A hub also called concentrator or multistation access unit (MAU). It provides a central point for cables in a network. Hubs also transmit signals and have multiple ports to which devices are connected. It broadcasts all messages to every computer on the network but only the intended recipient  computer takes the message.The computer that are not the recipients of the message ignores the message.A hub can handle only one-way  information traffic at a time.         

Data Communication

Data communication is a process of transferring data electronically from one place to another.Data can be transferred by using different medium.The basic elements of data communication are as follows: 

• Sender: The sender is the device that sends the information. It is also called source. Normally, computer is used as sender in data communication systems.

•  Medium :The medium is the physical path that connects the sender and the receiver.It is used to transmit the data. The medium can be a copper wire,a fiber-optic cable, airwaves etc. It is also called communication channel.

• Receiver: The receiver is the device that accepts the information. It is also called sink . The receiver can be computer, printer or another computer related device.

Types of Data Transmission

The two forms of data transmission are as follows:

1. Digital Data Transmission:

The transfer of data in the form of digital signal is called digital data transmission. Digital signal is a sequence of voltage represented in binary form. The digital signals are in the form of electrical pulses of ON an OFF.

Digital signals are faster and efficient.They provide low error rates . They also provide high transmission speed and high- quality voice transmission. All data communication between the computers is in digital form.Computers understand and work only in digital form. The following figure represents a high voltage as a 1 and a low voltage as a 0.

2. Analog Data Transmission

Analog data transmission is the transmission of data in a continuous wave form.For example sound waves are analog signals. When we talk, we emit sound waves that consist of waveforms of high and low pressure.Analog signal is measured in volts and its frequency is in Hertz (Hz). Telephone line is most commonly used media for analog transmission of data. light, sound, radio and microwave can also be used as analog transmission media.

Operating System of Computer

An operating system is a set  of programs that manages all computer components and operations. A computer cannot do anything without operating system. Operating system must be installed on every computer. Users interact with computer via operating system. When computer is turned on, the operating system runs and checks that all parts of the computer are functioning properly. Operating system runs and checks that all parts of the after loading. The following figure shows that an operating system is a set of program that acts as an interface between a user of a computer and computer hardware. Some popular operating system are DOS, windows, Unix, OS/2, Linux etc.

Functions of Operating System

Operating system performs the following functions:

• Booting: Booting is a process of starting the computer. Operating system starts the computer to work. It checks the computer and makes it ready to work. 

• Memory Management: The memory cannot be managed without an operating system. Different programs and data execute in memory at one time. If there is no operating system, the programs may mix with each other.

• Loading and Execution: A program is loaded in memory before it can be executed. Operating system provides the facility to load and execute programs.

 

• Data Security :Data is an important part of computer system. The operating system protects the data stored on the computer from illegal use, modification or deletion. 

•  Disk Management:Operating system manages the disk space. It manages the stored files and folders in a proper way.

•  Process Management:CPU can perform one task at one time. If there are many tasks, operating system decides which task should get the CPU.

• Device Controlling:Operating system controls all devices attached to computer.The hardware devices are controlled with the help of device drivers. 

• Printing Controlling:Operating System also controls printing function. If a user issues two print commands at a time, it does not mix data of these files and prints them separately.

• Providing Interface: User interface is used to interact with computer . It controls how a user enters data and instructions and how information is displayed on the screen.

Computer Software

A set of instructions given to computer to solve a problem is called software.Software is also known as program .Computer software specify a sequence of operations to be performed by computer.A computer works according to the instructions written in software.

Types Of  Software

The main types of software are system software and application software.

1. System Software:

System software is set of programs to control and manage the actual operations of a computer hardware.It controls the usage and allocation of different hardware components. It enables application programs to execute properly.It controls the basic operations as follows:

• Saving data on disk 

• Making computer to work for us 

• Printing a document etc.

Examples of System Software

Examples of system software are as follows:

• Operating System

• Utility Programs  

• Device Drivers

2. Application Software

Application software is a program needed to perform various applications on the computer by the user. It helps a computer user to solve specific problems. Different software packages are used on computer to ease the work. The application software uses the operating system in order to function. The operating system is the base software. The applications software runs on top of the operating system software.

Types of Application Software

Different types of application software are as follows:

• Word Processing: Word processing software is used to produce letters, applications and other documents. MS world is an examples of world-processing software. 
• Spreadsheets:  Spreadsheet program is used for calculations. It provides worksheets to enter data perform calculations using formulas and built-in functions. It can display data using charts and figures. MS Excel is an example of spreadsheet. 
• Databases:  Database is an organized collection of related data that is stored in an efficient and compact manner. It is used to store information and then search  this information quickly. MS Access and Oracle are examples of database software. 
• Graphics:  Graphics software is used to produce advertisements, posters etc. It is also used to draw pictures and figures. CorelDraw is an example of graphic software. 
• Communication software: Communication software is used to communicate with different people using Internet. The user can communicate by sending email or voice mail. MSN Messenger, Outlook Express, Mirc and Internet Explorer are examples of communications software.

Computer Buses

  A computer system consists of different devices.CPU must be able to communicate with all devices. The devices are connected together by a communications channel called bus. A bus consists of a set of communication lines or wires. It is used to move a large amount of bits in the form of electrical pulses from one unit to another. The bus is used to connect the following units:

• Central Processing Unit

1. Control Unit 
2. Arithmetic and Logic Unit

• Main Memory ( RAM, ROM)
• Input / Output Devices

Bus is a common path to transfer data and commands between CPU, memory and input / output devices.It is also used to send or receive data from secondary storage.The capacity of a bus depends on the number of data lines in it.A bus with 16 lines can carry 16 bits or 2 bytes at a time. A bus with 32 lines can carry 32 bits or 4 bytes at a time .

Types Of  Buses


Different types of buses are as follows:

1. Data Bus

2.Address Bus

3.Control Bus 

1.Data Bus:
Data bus is the most common bus. It is used to carry data.It is an electrical path that connects CPU, memory, input / output devices and secondary storage devices.The bus contains parallel set of lines. The number of lines affects the speed of data transfer between different components. A data bus with more lines can carry more data.A data bus with 16 lines can carry 16 bits ( 2 bytes ) of data. A bus with 32 lines can carry 32 bits ( 4 bytes ) of data.

2.Address Bus :
Address bus is used to carry address information. It is a set of wires similar to data bus. It only connects central processing unit and memory. The following steps take place when CPU needs data from the memory:

• CPU places the address of required data on address bus.
• The address is carried to the memory.
• The data from the requested address is fetched and placed on data bus. 
• The data bus carries the data to CPU.

The number of lines in the address bus determines the maximum number of memory addresses.If an address bus has 8 lines, the maximum number of memory locations that can be addressed are 2 = 256. The computers used today have 32 bit address lines .These computers can access 4GB of memory.

3.Control Bus:
Control bus is used to transmit different commands or control signals from one component to another component. Suppose CPU wants to read data from main memory. It will use control bus to send the memory read command to the main memory of computer. The control bus is also used to transmit control signals like ACKS( Acknowledgement  signals) A control signal contains the following:

• Timing Information:It  specifies the time for which a device can use data and address bus.
• Command Signal:It specifies the type of operation to be performed . 

Suppose that CPU gives a command to the main memory to write data . The memory sends acknowledgement signal to CPU after writing the data successfully.CPU receives the signal and then moves to perform some other action.

Storage Devices of the Computer

Storage devices are used to store data and programs permanently. These devices are used to store large volume of data and program. Storage devices are also called backing storage devices, secondary storage devices, or auxiliary storage devices. Two important instructions or information from storage medium to memory. Writing is a process of coping the data, instructions or information from memory to a storage medium.

Types of Storage Devices

Different types of storage devices are as follows:

1. Magnetic Tape
Magnetic tape is a flexible plastic tape coated with magnetic material. It is widely used when large amount of  data  is to be processed sequentially. An advantage of magnetic tape is that it is very cheap and economical storage medium. Its major disadvantage is that it is very slow and it is only sequential.


2. Magnetic Disk

Magnetic disk is the most widely used storage media. A magnetic disk is a thin, circular metal plate / platter coated with magnetic material. Information can be recorded on or read  from the magnetic surface. A disk must be formatted before it can be used. The formatting process prepares the disk so that it can store data. Formatting process creates tracks and sectors on disk. Each track on a disk is divided into sectors. Each sector  holds a specific number  of characters. A sector is the smallest physical storage unit on a disk. Its size is normally 512 bytes. The magnetic disk is a random access storage media. It means that any part of the disk is directly accessible.

Types of Magnetic Disk
Different types of magnetic disks are as follows:


a. Floppy disk or Diskette                            

Floppy disk is also called diskette. It consists of a thin plastic disk coated with magnetic material. This disk is enclosed in a plastic jacket. It  can store a small amount of data. Data access speed of floppy disk is slower than hard disk. It is inexpensive storage media. The standard size of floppy disk is 3  1/2 inch and its capacity is 1.44MB. The circular piece of plastic on 3  1/2 inch disk is enclosed in a shell. A piece of metal covers the reading and writing area. It is called shutter. When the disk is inserted into a disk drive, the shutter opens to read the stored data with floppy disk drive. The read / write head in floppy disk drive is used to read and write data on floppy disk.




b. Hard Disk

Hard disk is a type of magnetic disk. It is also called fixed disk  because it is fixed in the system unit. A hard disk  consists of several circular disks called platters sealed inside a container. The container contains a motor to rotate the disk. It also contains an access arm and read/write head to read and write data to the disk. The platters are used to store data. A platter in a hard disk is  from 320GB and more. It is much faster than floppy disks. The data stored on hard dis is safer than floppy disk. 

c. Zip Disk

Zip disk is a portable disk. It has more storage capacity than floppy disk. Its storage capacity is up to 1000 MB. Zip disk can be read / written by using Zip drive. It is used for taking the backup of large data.




Optical Disk

Optical disk uses laser technology to read and write data. The LASER stands for light Amplification through Stimulated Emission of Radiation. Laser beam writes on the surface by creating small pits (hole) in the disk.Optical drive reads data by focusing laser beam on the surface of the disk.A laser detects the presence of a pit.The presence of pit indicates 1and absence of pit indicates 0. Laser beam converts these pits into digital data.Optical disk storage capacity is from 600 MB to over 1 GB

Categories of Optical  Laser Disks:  

Different categories of laser disks are as follows: 

• CD-ROM:                                                                                                                                          

CD-ROM stands for compact disk read-only memory.The data stored on CD-ROM can only be read.It can cannot be deleted or changed.It is a portable storage device.It can be used to transfer data easily. It can store about 650MB of data . It is used to distribute new application software and games. Information can be stored on CD-ROM for many years.

• CD-R

CD-R stands for CD recordable. The user can write data on CD-R only once but can read it many times.The data written to CD-R cannot be erased.CD-R drives are known as CD burners and are typically used to create custom music CDs . The process of putting information on CD is burning the CD.CD-R is also called WORM(Write Once Read Many).

• CD-RW

CD-RW stands for compact disc rewritable.The user can write data on CD-RW many times by erasing the existing contents.Such disks are normally used for applications using large volumes of storage with little update activity.

• Digital Video Disk (DVD)

 DVD stands for Digital Video Disk.It is similar to CD-ROM. It uses a laser beam with short wave length. The short wave length reads smaller holes on the disk. Data storage capacity of the disk is increased if the hole size is small.So the storage capacity of DVD ROM is much greater than CD-ROM.It can store up to 17 GB of data.
Solid State Storage Devices
 The solid state storage devices or flash memory devices are unique among all storage devices.Some solid state storage devices are non volatile and some are volatile.These devices are portable and provide fast access to data.They use very little power.They are very useful to store data on mobile devices and transport data from once device to another.They are widely used in digital camera, MP3 music players, notebook computers and cell phones.
 Types of Solid State Storage Device
 
Different types of solid - state storage are as follows:
1.USB  F Lash DRIVE
 USB flash drive is also knows as pen drive or key chain drive. It provides much greater storage capacity than floppy disk or Zip disk.A flash drive can store 64 GB or more data.It can be plugged into any USB port. It is small and lightweight storage device. USB flash drive requires no card reader .The size of USB flash drive is similar to the size of highlighter.It is durable and can be carried on a key ring.

2.Flash Memory Cards.
Flash memory cards are widely used in PDA, digital  camera, cell phones and notebook computers. Generally, these card are not interchangeable.

Causes of Computer Virus

A computer virus is a program or set of programs or set of program or set of programs that can cause damage to computer system. It may disturb the normal working of a computer system. The code in computer virus is attached to some part of operating system or computer programs. The instructions in the code tell the computer to perform some task. This task is often destructive such as:

• A computer virus can damage data or software on the computer.
• It can delete some or all files on the computer sytem.
• It can destroy all data by formatting hard drive.
• It may simply display a large happy face on the screen.
• Some viruses only slow down the computer and cause no serious damage. 

Causes of Virus

A computer virus is passed from computer to computer. A virus can be attached to any file that is copied to computer system. The user may download files from Internet or copy programs on floppy disks that may contain viruses. These are the most common ways of getting a virus on computer system. Many virus are speed through emails. Generally, a user cannot get virus by simply reading an email. However, certain virus are very dangerous such as Klez. These viruses are automatically spread when the user opens the email. The virus is spread even if the user does not open the email attachment. Normally, a virus is activated when the user executes a program that contains virus. For example, a user may have downloaded a computer game from Internet that contains a virus. The virus will be activated when the user runs game on the computer.

Antivirus

Antivirus is a software that is user to detect and remove a virus on computer system. A virus can be stopped from entering the computer with the help of good antivirus program. The antivirus software checks all files to detect virus. It can be installed and configured to work in the background. The antivirus program should be used carefully. It should match with the operating system. For example, a Mac computer should use an antivirus program that is specially written for this system. Similarly, a computer with windows operating system should use an antivirus program that is specially written for Windows. A mismatched antivirus program may cause unstable behavior and may crash the computer system. New viruses are written everyday. The antivirus companies constantly update their antivirus programs to protect users from new viruses. Most popular antivirus companies are as follows: 

• McAfee

• Symantec

• Panda Software

Benefits

Some important benefits of using antivirus programs are as follows:

• Antivirus program protects important data from virus.

• It checks all files before they enter computer system.

• It alerts the user about the virus before it causes any damage to computer.

• It quarantines or eliminates a virus so that it may not harm computer.

Types of Memory of Computer

A component in the computer used for strong instructions and data is called memory.

Memory Measuring Units

The data is digital computers is represented  as a collection of bits. The smallest unit of data that can be used by a computer is called bit. A set  of 8 bits is known as byte. One byte is required to store one character. The capacity of main memory is often measured in the number of bytes. Different units to measure are as follows:

 UNIT                                                       No. of bytes

1 Nibble                                                    = 4 bits

1 Byte                                                       = 8 bits
1 Kilobyte (KB)                                        = 1024 bytes = (2) power 10 bytes
1 Megabyte (MB)                                     = 1024 KB = (2) power 20 bytes
1 Gigabyte (GB)                                       = 1024 MB = (2) power 30 bytes
1 Terabyte                                                = 1024 GB = (2) power 40 bytes

Types of Memory
Different types of memories are random access memory and read-only memory.

1. Random Access Memory (RAM)

2. Read-Only Memory (ROM)
3. Cache Memory
4. CMOS



1.Random Access Memory (RAM)

RAM stands for Random Access Memory. It is also called main memory or Direct Access Memory.  Random access means that each individual byte in the entire memory is directly accessible. A program must be loaded into RAM before execution. Most desktop computers usually have 2GB or less memory. RAM is temporary memory. When the power is turned off, the information in this memory is lost. Thus it is called volatile memory. CPU can read data from RAM and write data to ROM. That is whey RAM is also known as read / write memory. It is used to store data and instruction while it is being executed.

Types of RAM

RAM is built by using two different techniques:

a. Dynamic RAM

DRAM stands for Dynamic Access Memory. It is a type of memory that is used in most computers. It is the least expensive kind of RAM. It requires an electric current to maintain its electrical state. The electrical charge of DRAM decreases with time that may result is loss of data. DRAM is recharged or refreshed again to maintain data. The processor cannot access the data of DRAM when it is being refreshed. That is why it is show.

b. Static RAM
SRAM stands for Static Random Access Memory. It can store its value without any need to refresh the data as long as the power is available. SRAM is more expensive. It does not need to be power-refreshed. CPU does not wait to access data so it is faster. It utilizes more power than DRAM. It is normally used to build a very fast cache memory.

2.Read-Only Memory (ROM)

Rom stands for Read Only Memory. The instructions in ROM prepare the computer for use. These contents of ROM can only be read but cannot be changed or deleted. It is not possible to write new information or instruction in ROM. It stored data and instructions permanently. When the power is switched off, the instructions stored in ROM are not lost. That is why ROM is known as non-volatile memory.The data and programs in ROM are stored by the manufacturer. ROM is used to store frequently used data and instructions. The instructions in ROM are automatically loaded into the memory of computer when the computer is switched on.

Types of ROM
Different types of ROM are as follows:

1. PROM:

PROM stands for Programmable Read Only Memory. This form of ROM is blank. The user or manufacturer can write data and programs on it using special devices. The user can write data and instructions, the error cannot be removed from PROM. The chip becomes unusable.

2. EPROM:                                                           
 EPROM stands for Programmable Read Only Memory. This from of ROM is initially blank. The user or manufacturer can write data and programs on it using special devices. The data and programs written on it can be erased using ultraviolet rays. The user then can write new program on it.

                                                                           

3. EEPROM:
EEPROM stands for Electronically Erasable Programmable Read Only Memory.The user can erase and write instructions in EEPROM using electrical devices.The user can erase its contents electronically if any error occurs in writing instructions.The contents of EEPROM.

3.Cache Memory                                                                                        

Cache memory is designed to speed up the transfer of data and instructions. It is located inside or close to CPU. It is faster than RAM. The data and instructions .It is located inside or close to CPU. It is faster than RAM. The data and instructions that are most recently or most frequently used by CPU are stored in cache.The data and instructions are retrieved from RAM when CPU used them for first time. A copy of that data or instructions is stored in cache.The next time the CPU needs that data or instructions, it first looks in cache. If the required data  is found there, it is retrieved from cache memory instead of main memory. It speeds up the working of CPU.

4.CMOS

CMOS stands for complementary metal- oxide semiconductor.It stores configuration information of computer.The information includes the type of disk drivers, keyboard and monitor, current data & time and other start up information required during booting process. CMOS chip uses battery power toretain information even when the computer is turned off. The information in CMOS can be changed.

Central Processing Unit (CPU)

The central processing unit (CPU) is the brain of computer. It is the most important component of a computer. It is also called processor. A computer cannot work without CPU. All computers must have a central processing unit.

CPU is located on the motherboard. It performs all operations on data according to the given instructions. It can perform arithmetic and logical operations like addition, subtraction etc. It executes instruction and tells other parts of computer what to do. CPU consists of two main units called ALU (Arithmetic and Logic Unit) and CU (Control unit).

1. ALU (Arithmetic and Logic Unit) 

ALU is a part of CPU. Actual execution of instruction takes place in this part. All arithmetic and logical operations are performed in ALU. It consists of two units:

a)Arithmetic Unit

Arithmetic unit of ALU performs basic arithmetic functions such as addition, subtraction, multiplication and division.

b)Logic Unit

Logic unit of ALU performs logical operations like comparing two data items to find which data item is greater than, equal to, or less than the other.

2. Control Unit

Control unit is an important component of CPU. It generates signals to direct the entire computer system. It controls  and coordinates all activities of computer system. It does not execute program instruction by itself. It  directs other parts of computer to perform different tasks. Control unit communicates with arithmetic and logical unit, memory and other parts of computer system. Control unit also provides clock pulses. The pulses are used to regulate and control the speed of all operations in computer.

Register:

A register is a small high-speed memory inside CPU. The CPU contains a number of registers. Registers are used to store information being processed. These are temporary storage areas for instructions or data. The temporary results during processing are also stored in registers. Each register has a predefined function. Control unit manages registers for the following purposes:

• Input the instructions or data

• Store the instruction or data

• Transfer the instructions or data

• Perform arithmetic or logical operations at high speed.

High-Fiber Foods

Here are a few fiber-filled favorites to try that have many nutritional benefits as well as great taste:

• Spinach and dark green leafy vegetables are naturally low in calories and fill you up with their fiber content and their crunch factor.Plus because they take longer to eat your brain has time to register fullness before you've had time to load up on calories.Green leafy vegetables also contain many plant nutrients, antioxidants, and B-complex vitamins, which help to prevent cancer, heart disease, and degenerative neurological diseases.

 

• Tomatoes are unique in their ability to produce an amino acid called carnitine.This amino acid increases your body's basal metabolic rate, causing your body to burn fat at a faster rate.Any and all tomato products, from ketchup to tomato sauce,are great for your weight-reducing diet.Tomatoes also contain abundant amounts of vitamin C and an antioxidant called lycopene, which helps to prevent several types of cancer,including breast and prostate cancers.The combination of vitamin C and lycopene also helps to prevent the buildup of cholesterol in your bloodstream.

•  Beans have a high fiber content that helps to reduce the        absorption of both fat and calories from the intestinal tract, not to mention the fact that they help reduce your appetite by filing you up on fewer calories. Beans are also high in potassium and low in sodium, which helps to reduce the risk of high blood pressure and strokes.

• Sweet potatoes are, contrary to popular belief, excellent sources of vitamins and minerals and are considered good carbs. They are a great addition to any weight-loss program because of their high fiber content and their nutritional value. Sweet potatoes are good sources of vitamin C, B-complex vitamins, folic acid, potassium, vitamin A, and beta-carotene. These nutrients, combined with plant sterols found in sweet potatoes, are powerful antioxidants, which can help to lower cholesterol and lower your risk of heart disease. When sweet potatoes are eaten with their skin, they are a good source of both insoluble and soluble fiber.

• Asparagus is an excellent source of potassium, folic acid, beta-carotene, vitamin C, and the antioxidant glutathione, which helps to fight nasty free radicals, which can damage normal cells. Asparagus is a great addition to any diet program, since it is low in calories and high in fiber and nutrients. Steamed asparagus is great eaten alone or in a salad. Leftovers must be refrigerated or frozen quickly, however, to prevent the loss of nutritional value. Asparagus should be lightly steamed or roasted. If boiled too long, most of the nutrients end up in the water. 

• Peppers, including red, green, and yellow sweet peppers, are excellent sources of vitamin C, vitamin A, beta-carotene, B-complex vitamins, potassium, and folic acid. They are low in calories and high in fiber, so peppers are excellent foods to add to your weight-loss program. Because they are so flavorful, peppers satisfy your taste buds and help reduce your appetite. Pepper contain antioxidants, which help to prevent blood clots, thereby helping to prevent heart  attacks and strokes. Hot peppers have higher quantities of antioxidants than sweet peppers, as well as phytonutrients that assist in preventing certain forms of cancer. Hot peppers contain an ingredient, capsaicin, that not only makes them hot and spicy but gives them anti-inflammatory properties that help to relieve the pain of various forms of arthritis and nerve inflammations.  

 

Generations of Computer

The development of electronic computers can be divided into generations depending upon the technologies used. The generations of computers are as following:

First Generation Computers (1942-1955)

First Generation computers were used during 1942-1955. They were based on vacuum tubes. Vacuum tubes were the only electronic component available during those days. Vacuum tube technology made possible to make electronic digital computers. These computers heated very soon due to thousands of vacuum tubes. They used only machine language. Punch cards were used for input in these computers. Examples of first generation computers are ENIVAC  and UNIVAC-I etc

Second Generation Computers (1955-1964)

 The transistor was used in second-generation computers. Transistor are smaller, more reliable and consume far less power as compared to vacuum tables. Some examples of second-generation computers are IBM 7094 series, IBM 1400 series and CDC 164 etc.

Third Generation computer (1964-1975)

The major invention of third generation computer was the development of IC. IC stands for Integrated circuit. A single IC chip contains thousands of transistors. The computer became smaller in size, faster, more reliable and less expensive. Some examples of third-generation computers are IBM System / 360, UNIVAC 1108 and IBM 370 etc.




Fourth Generation Computers (1975-Present)

The fourth generation computers started with the invention of microprocessor. Microprocessor is a small chip containing thousands of ICs on it.It greatly reduced the size of the computer.The size of modern microprocessors is usually one square inch.It can contain millions of electronic circuits.The first microprocessor was produced by Ted Hoff in 1977 for Intel Corporation.The name of this microprocessor was Intel 4004.Examples of fourth generation computers are Apple Macintosh and IBM PC.


Fifth Generation (Present and Beyond)

The fifth generation computers are based on the technique of artificial intelligence .Computers can understand spoken words instructions and imitate human reasoning.The ability to translate a foreign language is also moderately possible with fifth generation computers.Scientists are trying to create a computer with real IQ with the help of advanced programming and technologies.

Output Devices

Output:

The data that has been processed into useful information is called output.

Types of Output:

Different types of output are as follows:

• Soft Copy: The output shown on display screen is called soft copy output.The common devices to produce soft copy are monitors and speakers.

• Hard Copy: The output printed on paper is called hard copy output.The common devices to produce  hard copy output are printers and plotters.

Output Devices:

The hardware components that are used to receive information from the computer are called output devices.Output devices take information from the computer and convert it in a from that is understandable by the users.

1. Printers

A printer is an output device that prints characters, symbols and graphics on paper . The printed output is called hard copy. Printers are commonly used in businesses to print different documents. 

Different categories of printers are as follows:

1. Impact Printers
2. Non-Impact Printers

1.Impact Printers:

An impact printer works like a typewriter.It prints characters or images by striking a print hammer or set of pins against an inked ribbon . The ink is pressed from ribbon on the paper to produce the output.Impact printers are the oldest print technologies which are still produced. The impact printers are used where low-cost printing is required.
Three most common forms of impact printers are as follows:

• Dot Matrix Printers                                                                               

• Daisy Wheel Printer

• Line Printer

1.Dot Matrix Printer:

A dot matrix printer is an impact printer.It produces printed images when tiny pins on a print head strike an inked ribbon. When the ribbon presses against the paper, it creates dots that from characters and graphics.The print head on a dot matrix printer can contain nine to twenty-four pins.A higher number of pins print more dots that produce higher quality.Dot matrix printers do not provide high quality
output.They produce a lot of noise while printing. The printing cost of these printers is very cheap.

2.Daisy Wheel printer:

Daisy wheel printer is similar to a typewriter.It uses a print wheel. The print wheel is called daisy wheel. Each petal of daisy wheel contains character. A motor rotates the wheel. A hammer strikes a petal against the ribbon when the desired character reaches the position on the paper. This prints the character on the paper. Daisy wheel printer is slower than dot matrix printer but better in quality.


3.Line Printer:
Line printer is a fast impact printer. It can print multiple characters on the sam line at a time. Its speed is measured in lines per minute (lpm). The speed range of line printer is from 300 LPM to to 2400 LPM. The line printers are faster than dot matrix and daisy wheel printers. They are more noisy and provide limited font capability. They produce lower print quality than recent printing technologies. Band printer and chain printer are the examples of line printers.

4. Non-Impact Printers:

A non-impact printer prints characters and graphics on paper without striking paper. The characters are printed on paper with some means such as laser. Some printers use spray ink while others use heat and pressure to create images. These printers are faster than impact printer. However, they are most costly than impact printers. They produce no noise during printing. The print quality of non-impact printers is better than impact printers. Different kinds of non-impact printers are laser printer and inkjet printer.

Different types of non-impact printers are as follows:

a. Laser Printer 
Laser printers are non-impact printers. Its working similar to  a photocopying machine. The laer printer creates image on the paper by laser beam. LASER stands for Light Amplification by Stimulated Emission of Radiation. Laser throws magnetic material powder on paper in the form of microscopic dots. The density of these dots ranges from 300 to 2000 Dots Per Inch (DPI). The printing speed of laser printers can be from 5 to 300 pages per minute (ppm). Laser printers are also called page printers. They print complete page at a time. They produce very high quality print. They are faster than inkjet and dot matrix printers. Laser printers are mostly used in business field.

b. Inkjet Printer                                               
An ink-jet printer is a type of non-impact printer.It prints characters and graphics by spraying tiny drops of liquid ink on paper .These printers can produce quality text and graphics in both black- and white and color. 
Inkjet prints are slower than laser printers. They can print 1 to 6 pages per minute.Its print quality is higher than dot matrix printer.They are also relatively inexpensive.
2. Plotter:
A plotter is an output device that is used to produce image-quality graphics a variety of colors . Plotters are used to create maps, architectural drawings, graphs and charts. A plotter works by drawing lines on paper using pens held in a mechanical arm.



3. Monitor or Display Screen:
Monitor is the most common output device. The output displayed by monitor is called soft copy. A monitor looks like a television and displays text and graphics. Different display screens can distinguished on the basis of the following features:

• size
• colors
• Resolution
• Video Display Adapters
• Refresh Rate
• Dot pitch

Types of Display Screens

1. CRT Monitor
CRT monitor is the most common form of display screen. It can display text and graphics. It uses a cathode ray tube (CRT) that creates an image by an electronic beam.CRT consists of one or more guns that fire a beam of electrons inside the screen .The screen is coated with very tiny phosphor dots from inside. The beam of electrons repeatedly falls on the surface of screen.CRT  in color monitors consists of three guns. These guns generate red, green and blue (RGB)colours.
2. Flat panel Monitors :
Laptop PCs use flat - panel monitors.These monitors take less space. Flat panel monitors use a variety of technologies.The most common technology is LCD  .LCD monitors use much less power than CRT monitor.These monitors are available in different sizes such as 15'' , 17'' 18'' 21'' 23''.
4.Speakers & Headsets

A type of output produced in the form of sound, voice or music is known as audio output. Speakers and headsets are two commonly used audio output devices.Many personal computers have internal speaker. Headsets are also used to produce audio output.


5. Data Projectors:
Data projector is an output device that projects the output of computer screen onto a larger screen. The output projected by data projector can be viewed by a number of people very clearly.Data projectors are used in classes to deliver lectures to many students etc.