Grade-12 (Function and Structure)

1.       What is function? Write its advantages.

Ans: A function is a self contained block of statements that perform some specific and well defined task. A function can be user or predefined (library) function.

Advantages of function

a.       Function increases reusability of program code.

b.      Program development is faster.

c.       Program debugging is faster and easier.

d.      Length of the program can be reduced.

e.      With function, it is easier to understand the logic involved in the program.

f.        Function reduces program complexity.

g.       Recursive call is possible through function.

h.      Function increases program readability.

2.    What are the differences between library function and user defined function. Write a program using user defined function to calculate y raise to power x.

        Differences between user defined function and library function:

Library function	User defined function
a. It is a predefined function in a header file or preprocessor directive. b. Programmer can simply use this function by including respective header files. c. The program using library function will be usually short as the programmer doesn’t have to define the function. d. Program development time will be faster. e. Example. Printf( ), getch( ), strlen( )	a. User defined function is not a predefined function. It is defined by the programmer according to the need. b. Programmer has to declare, define and use this function by them. c. The program using user defined function will be usually lengthy as the programmer has to define the function. d. Program development time will be usually slower. e. Example: Sum( ), area( ), Factorial( ), etc.

C Structures

Structure is a user-defined data type in C language which allows us to combine data of different types together. Structure helps to construct a complex data type which is more meaningful. It is somewhat similar to an Array, but an array holds data of similar type only.
Differences between array and structure

ARRAY	STRUCTURE
An array is a collection of variables of same data type.	A structure is a collection of variables of different data type.
type array_name[size];	struct sruct_name{ type element1; type element1; . . } variable1, variable2, . .;
Array elements are stored in contiguous memory location.	Structure elements may not be stored in a contiguous memory location.
Array elements are accessed by their index number.	Structure elements are accessed by their names.
Array declaration and element accessing operator is "[   ]" (square bracket).	Structure element accessing operator is "." (Dot operator).
Array name points to the first element in that array so, array name is a pointer.	Structure name does not point to the first element in that   structure so, structure name is not a pointer.
Objects (instances) of an array can not be created.	Structure objects (instance or structure variable) can be created.
Every element in array is of same size.	Every element in a structure is of different data type.
Bit filed can not be defined in an array.	Bit field can be defined in a structure.
There is no keyword to declare an array.	"struct" is a keyword used to declare the structure.
Arrays are not user-defined they are directly declared.	Structure is a user-defined datatype.

# Write a program to read 100 different number from users, store them in an array, passes the array through function and find maximum number among them.

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Compjter Network Grade-XII

 Grade-XII (Computer Network)
1. What do you mean by computer network? Explain its advantages and roles of hardware.
Computer Network
The dictionary defines a network as a “group of computers and associated devices that are connected by communications facilities.” Thus, a network can be anything from two computers connected by a serial cable to thousands of computers connected by high-speed data communication links dispersed throughout the world. In other words, computer network is a group of computers and associated peripherals connected by a communications channel capable of sharing files and other resources between several users.
Benefits of Networking:
A network provides three principle benefits: the ability to communicate, the ability to share hardware and software, and administrative support.
a). Information sharing and communicating:
The ability to communicate and share of information, inexpensively is one of the popular benefits of networking technology. A network supports communication among users in ways that other media cannot. E-mail, the most popular form of network communication, provides low-cost, printable correspondence with the capability for forwarding, acknowledgment, storage, retrieval, and attachments.
b). Sharing of hardware and software:
Sharing involves not only information (database records, e-mail, graphics, etc.), but also resources (applications, printers, modems, disk space, scanners, etc.) Through its ability to share, a network promotes collaboration. This is the main attraction of popular software called “groupware” that is designed to allow multiple users to hold electronic meetings and work concurrently on projects
c). Centralized administration and support:
Networking simplifies administration and support tasks. The network administrator can perform administrative tasks on any computer on the network from just a single location. Also, it is more efficient for personnel to support one version of OS or application than to oversee a number of individual and unique systems and setups.
Roles of computers in a network:
The computers in a network functions as either clients or servers. The roles of computers in a network are;
a). Clients:
A client is a computer that uses the resources made available by a server. The client must have sufficient processing power on its own to run applications that interact with the resources on the server.
b). Server:
A server is a computer that makes its resources available to the network and responds to the commands of a client. The server in a network performs a variety of complex tasks. The following are some examples of different types of server included on many large networks:
i). File and Print Servers:
File and print servers provides file and printer resources from a centralized location. When a client sends a request for data to the file and print server, the entire database or file is downloaded to the computer making the request. Once the document is saved back on the server, anyone on the network who has the proper access, or permission, may look at the file. In other word, file and print servers are used to store and retrieve centralized file and data records.
ii). Database Servers:
Database servers can store large amount of data in a centralized location and make this data available to users so that they do not need to download the entire database. With a database server, the entire database stays on the server and only the results of a request are downloaded to the computer making the request.
iii). Mail Server:
Mail server operates like database servers. Mail servers manage the e-mail services for the network.
2. Explain the different types of Network:
Network models classify the network on the basis of services and geographical area.
I). Network based on services:
Based on how the computers in a network are configured and how they access information, networks are classified into two types;
a). Peer-to-Peer Network:
In a peer-to-peer network, all computers have an equal relation to one another. There is not any computer, which can be regarded, as superior to another computer. All computers are equal and therefore are known as peers. Any computer in peer-to-peer network can functions as both client and a server simultaneously. Any computer in the network is capable of accessing data, software and other resources directly without any central controlling mechanism. Peer-to-peer network are also called as workgroups.
Advantages of using peer-to-peer network:
• Peer-to-peer networks are easy to build and operate
• Peer-to-peer networks are inexpensive to operate
• The network software used to operate peer-to-peer networks are simple and easy to operate.
• If any computer in a peer-to-peer network fails, then the resources on only that computer becomes unavailable without hampering the availability of resources on other computers.
Disadvantages of using peer-to-peer network:
• The required resources are difficult to find quickly because it could be in any one of the computers.
• Peer-to-peer networks are not very secure.
• A peer-to-peer network becomes very difficult to manage and operate when the number of computer involved exceeds 15 to 20.
b). Client-Server Network:
Client server networks have become standard models for networking. In client-server network, there is a clear distinction between the computers depending upon their functionality; clients and servers. Servers are powerful computers dedicated to managing files or documents (file server), printers (print servers), web pages (web servers) etc. Client are less powerful computer on which users do their job. Client depends upon server computers to access required resources.
Advantages of using client-server network:
• Since the resources are usually located in servers, the resources are easy to find.
• Client-server network can be made very secure. The resources on the server can be controlled very tightly by identifying, who can access the resources and who cannot.
• Client-server network are very scalable. i.e. the number of clients that can be connected in a client-server network is not limited.
Disadvantages of using client-server network:
• It cost more to implement and operate than the peer-to-peer network.
• If the server in a client-server network fails, then the clients cannot access any resources.
• Specialized software is needed to implement a client-server network.
II. Network based on Geographical Area:
1). Network based on Geographical area:
Based on size and distance coverage of networks, the computer network is divided into three types:
a). Local Area Network:
A local area network (LAN) refers to a combination of computer hardware and transmission media that is relatively small. Normally, LAN is entirely contained within a school, college, building etc. LANs is typically comprised of only one transmission media type such as coaxial cable or twisted pair cable but never both. The features of LAN are;
• It covers short geographical area.
• LANs are characterized by comparatively high speed communication.
• LAN uses only one kinds of cable.
• Complete ownership by single organization.
b). Metropolitan Area Network:
A Metropolitan Area Network (MAN) is a network that is larger than a LAN. It is called metropolitan since it normally covers the area of city. Different hardware and transmission media are often used in MAN because they don’t require complete access to locations between the network sites. The features of the MAN are;
• It covers large geographical area with respect to LAN.
• MANs typically used when you need to connect dissimilar system within a single metropolitan.
• It is owned by single or multiple organizations.
• It uses private or public connection mediums.
c). Wide Area Network (WAN):
A Wide Area Network is a network of connecting two or more computers generally across a wide geographical area such as cities, districts and countries. WANs interconnect LANs which may be at the opposite side of a country or located around the world. It uses telephone lines, communication satellite and other long range communication links to connect the computers and network. Internet is an example of WAN. The characteristics of WAN are:
• It covers a large geographical area.
• Transmission cost is high
• Transmission error is higher than LAN
• It is owned by multiple organizations.
• It uses public connections mediums such as telephone lines, wireless technology etc.
• Owned by multiple organization.
3. What is Network Topology/LAN topology/Topology? Explain different types of topologies with merits and demerits.
A network topology is the physical arrangement of computers, cables and other components on a network. The type of topology you use affect the speed and performance of the computer network. The common used physical network typologies are; Bus Topology, Ring Topology, Star Topology, Mesh Topology, Tree Topology, Hybrid Topology
a). Bus Topology:

In a Bus topology, all devices attach to the same transmission medium. The medium has a physical beginning and end. All buses are implemented using electrical cable, usually coax, and the ends of the cable must be terminated with a terminating resistor that matches the impedance of the cable. The terminating resistor prevents data reflections from coming across as data corruption. The bus is considered a multi-point system because all devices tap into the same backbone cable.

 Advantages:
• Bus topology is simple, reliable (in very small network), easy to use and easy to understand.
• It is less expensive.
• It is easy to add a new node in the network.
Disadvantages:
• Heavy network traffic can slow a bus considerably.
• It is difficult to troubleshoot.
• If problems occurs on the backbone, the entire network will go down.
b). Star Topology:
 In a star network, each node (file server, workstations, and peripherals) is connected to a central device called a hub. The hub takes a signal that comes from any node and passes it along to all the other nodes in the network. Data on a star network passes through the hub or switch, before continuing to its destination. The hub or switch manages and controls all functions of the network. The star topology reduces the chance of network failure by connecting all of the systems to a central node.
Advantages:
• It is easy to set up and configure.
• It is easy to modify and add new computers to a start topology without disturbing the rest of the network.
• Single computer failure does not necessarily bring down the whole start network.
• It is easy to detect the errors in star topology
Disadvantages:
• It the central device fails, the whole network stops.
• It costs more to cable a start topology because all network cable must be pulled to central point (hub).
c). Ring Topology:

In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction.  A failure in any cable or device breaks the loop and can take down the entire network. To implement a ring network it could use the Token Ring technology. A token, or small data packet, is continuously passed around the network. When a device needs to transmit, it reserves the token for the next trip around, then attaches its data packet to it.

Advantages:
• Ring topology is easy to setup and reconfigure.
• Each computer is given equal opportunity to access the network resources.
• Single cable connects between the nodes.
Disadvantages:
• Failure of one computer on the ring can affect the entire network.
• Adding or removing computers disturbs the networks.
• It is difficult to troubleshoot in a ring topology.
d). Mesh Topology:

In this topology, each node is connected to every other node in the network. Implementing the mesh topology is expensive and difficult. In this type of network, each node may send message to destination through multiple paths. While the data is travelling on the Mesh Network it is automatically configured to reach the destination by taking the shortest route.

Advantages:
• The mesh topology is fault tolerance.
• It is easy to troubleshoot.
Disadvantages:
• Difficult to installation and reconfigure
• It is costlier.

4. What are the components of Components of Computer Network? Explain.
The communication between two computers is possible by interacting between hardware and software Components.
1). Hardware Components:
All the physical component of network that is used to connect or communicate is hardware components. The different hardware components are:
1 Server:
A server is a computer that makes its resources available to the network and responds to the commands of a client. The server in a network performs a variety of complex tasks. It is the main computer in network which has high storage capacity and high processing speed. The following are some examples of different types of server included on many large networks:
i). File and Print Servers
ii). Database Servers
iii). Mail Server
2. Client / Workstation:
A client is a computer that uses the resources made available by a server. The client must have sufficient processing power on its own to run applications that interact with the resources on the server. It is also called as work station
• Cables:
Cables are the pathway or channel along which the signals or data can be transmitted from one point to another. The most commonly used cables are coaxial, twisted pair and fiber optics.
• Network Interface Card:
Network Interface Card is the computer circuit board or card that is installed in a computer so that it can be connected to a network by using physical channel. Each NIC is assigned a unique MAC (Media Access Control) address by the manufacturer through which data is sent to the destination. The main function of NIC is to convert data into electrical signals and transfer them through cable and vice versa.
• Hub:
Hubs are centrally connectivity devices that connect computers in a star topology. Hub contains multiple ports for connecting to network components. It amplifies (increase) the signals and sends them to all connected devices. Use of hub has become very common in most of the computer networking as it cost lower and easier to install.
• Connectors:
It is an interface between NIC of the computer and the cable that passes data from one computer to another. It depends on type of cable and devices used in the network. The different types of connectors are; BNC connector, RJ 45, ST, RJ 12 etc.
• Repeater:
A repeater is a physical layer device used to interconnect the media segments of an extended network. It amplifies the incoming signals, creates a new copy of it and transmits the signals on the network. A repeater essentially enables a series of cable segment to be treated as a single cable.
• Bridge:
A bridge is a device that passes data packets between multiple network segments that use the same communication protocol. A bridge passes one signal at a time. It filters the data or inspects incoming signals and decides whether to forward the signals or discard them.
• Switch:
Switches are similar to bridge but offer a more direct network connection between the source and destination computers. The main difference between bridge and switch is the way that filtering happens. With a switc0h, filtering and performance better than bridge.
• Router:
Router is a device that acts like a bridge or switch but provides more functionality. It uses addresses for filtering and forwarding the data. Router enable all user in a network to share a single connection to the Internet or a WAN.
• Gateway:
A gateway is a device that enables communication between different network architecture. A gateway takes the data from one network and repackages it, so that each network can understand the other network’s data.
• Modem: (Modulation-Demodulation)
A modem is a communication device that enables a computer to transmit information over a standard telephone line. A modem is required when connecting to the Internet using telephone line. It is an essential link between the computer running browser and dial up service providers. A modem is needed to convert digital signal to analog signal and vice versa.
Analog Signal:
An analog signal is a constantly changing electrical wave signal that changes in a rounded or smooth pattern.
Digital Signal:
A digital signal uses a square waveform, which is reliably used to transmit electronic data.
5. What is transmission media? Explain guided media
Transmission Media / Communication Media / Network Media:
Communication media is the pathway or channel along which the signals or data can be transmitted from one point to another. The signal transmitted from one device to another is through electromagnetic signals. It includes voice, radio waves, infrared light etc. The transmission media is divided into two types:
1) Guided Media:
In guided media is a media that uses a transmission carrier to send data signals through a contained conductor. This conductor can be a metal wire through which electricity flows or a glass strand through which pulses of light flows. The different types of guided media are:
a). Twisted Pair:
Twisted pair cable is the oldest and common medium of transmission. Twisted pair cable consists of two insulated strands of copper wire twisted around each other. There are two types of twisted pair cable. There are:
i). Unshielded Twisted Pair (UTP):
UTP cable consists of a number of twisted pairs of wires with a simple plastic casing. UTP is commonly used in telephone system. It is suitable for both data and voice transmission. It comes in different categories (cat 1 to cat 7). The bandwidth of the cables depends upon the category of the cable. UTP is good for noise rejection and it covers a maximum distance of 100m.
ii). Shielded Twisted Pair (STP)
The STP cable is similar in construction to UTP except that the twisted pairs are enclosed in a woven copper and foil wrap shield for providing extra protection from external interference. STP is more difficult to install than UTP and Coaxial cable. It covers shorter distance than UTP, but it has better noise rejection capacity. The STP is more costlier than UTP cables.
b). Coaxial cable:
Coaxial cable is made of two conductors that share a common axis. The center of the cable is a relatively stiff solid copper wire insulating by plastic foam. The foam is surrounded by the second conductor, a wire mesh tube, which serves as a shield from electromagnetic interference (EMI). The coaxial cables are used in communication networks with single ended single reference where the central conductor carries the data signals. The Connectors used in Coaxial cable are BNC, T-connector and terminals.
c). Fiber Optics:
Fiber-optic cable is made of a light conducting glass or plastic core surrounded by more glass called cladding and a tough (hard) outer cover. A fiber optic consists of a bundle of glass threads, each of which is capable of transmitting message modulated onto light waves. Fiber optics uses light signals rather than electricity, so it offers high bandwidth and greatest distance of any transmission system. The main disadvantage of fiber optics are; it is costlier to produce, maintain and install. The connectors used in fiber optics are Screw Mounted Adaptors (SMA), Spring-loaded Twist (ST), SC and FC.

Q. What is ISO reference model? Explain its different layer.
It is based on a proposal developed by the international organization for standardization (ISO). The model is called ISO reference model, because it deals with connecting open system i.e. the system that are open for communication with other system.
a. Physical Layer: This layer concerned with transmission of bit it determines voltage level for 0 & 1. It also determines the data rate of the system. This layer involves standardized protocol dealing with electrical & signaling interface.
b. Data Link Layer: It handles error in physical layer. This layer ensures the correct delivery of frame to the destination address. It consists of 2 parts or 2 sub-layers. i.e.
i. Logic Link Control & ii. Media Access Control
c. Network Layer: This layer is concerned with transmission of packet. Network layer protocol chooses the best path to send a package called routing. Two protocols are widely used in n/w layer.
i. X.25 Protocol & ii) Internet Protocol
d. Transport Layer: It provides the mechanism for the exchange of data between end systems. It ensures that the data received is in fact in order. Following jobs are performed by this layer.
i. Port Addressing ii) Segmentation & Reassemble & iii) Connection Control
e. Session Layer: It is responsible for requesting logical connection to be established for communication process. This logical connection is termed as session. It also provides data synchronization (organization) between two communication terminals.
f. Presentation layer: This layer translates format data to adapt to the needs of the application layer & nodes at both receiving & sending end of communication process. It handles data communication, formatting, encryption, decryption, etc.
g. Application Layer: It is the top-most layer of OSI model & provides user access to the n/w. It provides services that support user application, such as database access, email & file transfer, etc.

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Grade:XI (Computer System)

1.    What is computer system or computer architecture? Explain the major units of computer system.

Ans: Computer architecture is defined as the science of selecting and interconnecting hardware components to create computers that meet functional performance and cost goals.

                     

                                                                                                                                                                  

Main components of computer system are explained below:

1.    Input Device

        Those devices which are used to input data and instructions to the computer generating electrical signal and convert into computer format for the further processing is called input device. E.g. Mouse, scanner, joystick, etc.

2.    Processor (CPU)

        Processor is the main component in computer, that is the heart of the computer system with circuitry to control the interpretation and execution of instructions. The internal components of microprocessor are as follows:

a.    CU (Control Unit)

Control unit controls the sequence of actions by the program and Input/ Output operation. It is nerve center of CPU. It controls the flow of data within the devices and supervises on the data flow.

b.   Arithmetic and logic unit (ALU)

It performs all type of arithmetic calculations such as addition, subtraction, multiplication and division and it also performs the logical and comparative analysis like AND, OR, NOT operator.

c.    Register arrays

It  is a temporary storage built inside a microprocessor to store a data before and after storing data in primary memory. The speed of the microprocessor is evaluated by number of registers in the microprocessor itself.

3.    Primary memory

      The internal memory unit which stores all currently being used data and instructions temporarily. It stores the data that before processing or displaying and it also provide space to the CPU for data processing. It is directly accessed by CPU.  

It has two types which are RAM and ROM.

RAM: It stands for Random Access Memory that stores currently being used data and instruction and provide space to the CPU. It is volatile memory as its contents can be edited and deleted. Its data are erased when the electricity is cut off so called electrically dependent memory.

ROM: It is read only memory. It is permanent built in memory stores firmware and check all the status of computer while booting the computer. It is non volatile type and electrically independent as its contents can not be deleted and altered even doesn’t erased when the electricity is cut off.

4.    Secondary Storage Device

        Secondary memory is where programs and data are kept on a long-term basis. Common secondary storage devices are the hard disk and optical disks. The hard disk has enormous storage capacity compared to main memory. The hard disk is usually contained inside the case of a computer. Some examples are: Optical disk, magnetic disk, flash memory, etc.

5.    Output device

Output devices are those devices which display the required result in simple words to the users. The output device provides the output of data or information. The purpose of the output devices is to translate data and information from electrical impulses to a human-readable format. There are two principal kinds of output. They are described below:

• Soft copy output

It refers to data that is shown on a display screen or sound produced by a speaker. It is present in a digital form on a computer. This kind of output is untouchable. It is temporary in nature. For example, content displayed on a screen.

• Hardcopy output

It refers to printed output printed on the paper or some material that can be touched and carried for being shown to others. It is permanent in nature and can keep in paper files or can be looked later when a person is not using the computer. For example, outputs produced on paper by printer or plotter in the form of text or graphics, etc.

2. What are input device? Explain.
Those devices which are used to input data and instructions generating electrical signals and converted it into computer understandable form for processing is called input device.
Keyboard
Keyboard is the most basic input device. It is used for text input. It contains multiple keys. User can provide input by pressing the key. The different types of key found in keyboard are:
a) Alphanumeric keys
b) Function keys
c) Special function keys
d) Cursor movement keys
e) Punctuation keys
f) Numeric pad
g) Multimedia keys
a. Mouse
Mouse is a most common pointing and selecting device. It is used in graphical user interface. Mouse contains buttons for providing inputs. User can provide inputs by moving the mouse and pressing the button. On the basis of working mechanism and its architecture, mouse can be classified as
a) Mechanical mouse
b) Optical mouse
Mechanical mouse contains a rubber ball and a pair of rotating wheels. When the mouse is moved on the table, the ball rotated which results in rotation of the wheels and generates electronic signal.
Optical mouse operates using reflection of light. It is easier to use but usually less reliable than mechanical mouse.
b. Track ball
Trackball is the modification of mechanical mouse. It contains rubber ball on its top. User can move the cursor by rotating the ball with finger. It also contains two buttons on the either sides similar to mouse. It was used in older laptops.
c. Track pad/Touch pad
Track pad is the modification of optical mouse, and touch pad is further modification making it touch sensitive. It contains a window with two buttons on the either sides. User can also provide left click option by tapping the window with the finger. It is mainly used in portable devices like laptops, notebook, palmtop, etc.
d. Joystick
Joystick is a hand held pointing device which is mainly used for playing games. It is used for controlling objects, their movement, direction and speed of movement. Modern joysticks handle can move in any direction. When the handle is moved, the electronic circuit in the base detects the movement and sends corresponding binary signals to CPU.
e. Light pen
Light pen is used for creating drawings, designs by directly touching the screen. It is mainly used by designers, architects, engineers, etc. it is used in monitor not having touch screen facility. It is a pen shaped structure containing photo sensitive tip which can capture light emitted from the monitor and mark the position on the monitor.
f. Touch screen
Touch screen is none of the common input device at present mainly for portable computers. User can provide inputs by directly touching the screen with the metallic pen (stylus), finger or any pointed object. Touch screen is developed by using either of the following technologies:
a) Pressure sensitive
b) Capacitive
c) Infrared
g. Scanner
Scanner digitizes hard copy or printed images which can be used in digital computers. Scanner copies the image and draws a new digital image in its memory similar to hard copy image.
h. OCR (Optical Character Reader)
OCR digitizes handwritten or printed text.
Printed text will have fewer errors than hand written. It directly converts hand written text into digital text which can be edited. OCR contains predefined format of all the characters. During digitizing process, it creates an image of the character and compares it with stored format to determine the character.
i. MICR
It stands for Magnetic Ink Character Reader. MICR is an OCR that can digitize text written or printed by using magnetic ink like iron oxide or barium ferrite. It is used in security systems and for processing cheque in bank.
j. OMR
It stands for Optical Mark Reader. It is used for answer sheet correction in multiple choice questions. With the use of OMR answer sheet correction will be faster and error free.
k. BCR
It stands for Bar Code Reader. Bar codes are the magnetic lines used for storing the information about the product like manufacturing date, expiry date, company name, etc. BCR is used to read the information stored in bar codes. Bar codes are also used in security system.
l. Microphone
It is an input device for sound. It captures sound wave, converts it into digital format and provides it to the CPU. Common mobile computing devices like PDA, smart phone contains microphone.
m. Digital camera, Web camera
Digital camera captures real time images and video and stores it in a digital format. The image captured by digital camera can be directly used in a digital camera.
Web camera is a digital camera used in internet. It usually captures low quality images so that it could be transmitted at a faster speed.
n. Card reader
It is used to read the information stored in cards like ATM card, Credit card, Smart card, etc.
o. Digitizing tablet
It is used to digitize large map or hardcopy images. It is also used to track the movements of living beings and capture them in digital format.

3. What is computer Memory? Explain its types.
Computer Memory– Memory is storage part in computer. It is store the data, information, programs during processing in computer. It stores data either temporarily or permanent basis. Memory used to play important role in saving and retrieving data.

Types of Memory– Mainly computer have two types memory
1. Primary Memory / Volatile Memory.
2. Secondary Memory / Non Volatile Memory.
1. Primary Memory / Volatile Memory– Primary memory is internal memory of the computer. It is also known as main memory and Temporary memory .Primary Memory holds the data and instruction on which computer is currently working. Primary Memory is nature volatile. It means when power is switched off it lost all data.
Types of Primary Memory– Primary memory is generally of two types.
1. RAM
2. ROM
1. RAM (Random Access Memory) – It stands for Random Access Memory.RAM is known as read /writes memory. It generally refereed as main memory of the computer system. It is a temporary memory. The information stored in this memory is lost as the power supply to the computer is switched off. That’s why RAM is also called “Volatile Memory”
Types of RAM– RAM is also of two types:
a) Static RAM- Static RAM also known as SRAM ,retain stored information as long as the power supply is ON. SRAM are of higher coast and consume more power .They have higher speed than Dynamic RAM
b)Dynamic RAM– Dynamic RAM also known as DRAM, its stored information in a very short time (a few milliseconds) even though the power supply is ON. The Dynamic RAM are cheaper and moderate speed and also they consume less power.
2. ROM (Read Only Memory) – It stands for Read Only Memory.ROM is a Permanent Type memory. Its content are not lost when power supply is switched off. Content of ROM is decided by the computer manufacturer and permanently stored at the time of manufacturing. ROM cannot be overwritten by the computer. It is also called “Non-Volatile Memory”.
Type of ROM: ROM memory is three types names are following-
a. PROM(Programmable Read Only Memory)-PROM chip is programmable ROM.it is PROM chips to write data once and read many.once chip has been programmed ,the recorded information cannot be changed. PROM is also nonvolatile memory.
b. EPROM (Erasable Programmable Read Only Memory)- EPROM chip can be programmed time and again by erasing the information stored earlier in it. Information stored in EPROM exposing the chip for some time ultraviolet light .
c. EEPROM (Electrically Erasable Programmable Read Only Memory)-The EEPROM is programmed and erased by special electrical waves in millisecond. A single byte of a data or the entire contents of device can be erased.
2. Secondary Memory / Non Volatile Memory– Secondary Memory is external memory of the computer. It is also known as Auxiliary memory and permanent memory. It is used to store the different programs and the information permanently. Secondary Memory is nature non volatile. It means data is stored permanently even if power is switched off.
The secondary storage devices are:
1. Floppy Disks
2. Magnetic (Hard) Disk
3. Magnetic Tapes
4. Pen Drive
5. Winchester Disk
6. Optical Disk(CD,DVD)
1. Floppy disk
A floppy disk is a magnetic storage medium forcomputer systems. The floppy disk is composed of a thin, flexible magnetic disk sealed in a square plastic carrier. In order to read and write data from afloppy disk, a computer system must have a floppy disk drive (FDD).
2. Magnetic tapes
A magnetic tape drive is a storage device that makes use of magnetic tape as a medium for storage.
It uses a long strip of narrow plastic film with tapes of thin magnetizable coating. It is essentially a device which records or perhaps plays back video and audio using magnetic tape, examples of which are tape recorders and video tape recorders.
3. Hard disk Drive
A hard disk drive (HDD) is a non-volatile computer storage device containing magnetic disks or platters rotating at high speeds. It is a secondary storage device used to store data permanently, random access memory (RAM) being the primary memory device. Non-volatile means data is retained when the computer is turned off.
A hard disk drive is also known as a hard drive.
4. Winchester Disk
An early removable disk drive from IBM that put the heads and platters (disks) in a sealed unit for greater speed. Before the Winchester architecture, removable disks were like removable disks today, in which the read/write heads remain in the drive and make contact with the platter after the cartridge is inserted.
5. Pen drive
A pen drive, or a USB flash drive, is a portable data-storage device. Pen drives have replaced the floppy drives of old and have become the most popular data-storage devices among consumers. Micro, lightweight and handy, a pen drive can be easily carried from place to place by students, professionals, academicians and independent tech consultants. Currently available pen drives with storage capacities ranging from 8GB and 32GB can be used to store graphics-heavy documents, photos, music files and video clips.
6. Optical Disk (Optical Memory)

Optical memory uses light beam for its operation. It is developed in fourth generation of computer. It is mainly used for storing audio/video, backup as well as for carrying data. It requires optical drive for its operation. Its read/write speed is slower compared to hard disk and flash memories.
Example: CD, DVD, BD

CD
It stands for Compact Disk. It has storage capacity of 700 MB or approximately 90 minutes of standard audio. CD contains hard circular plastic, single side of this plastic is coated by aluminum alloy. This alloy stores data. It is protected by additional thin plastic covering. CD required CD drive for its operation. Types of CD are:
CD-R is a blank CD in which data can be stored once. After storing data it is converted into CD-ROM.
CD-ROM
It cannot be erased or updated
CD-RW
It is an optical disk stands for compact disk re-writeable. it can be erased and used for multiple times.
DVD
It stands for Digital Versatile Disk. It has the storage capacity of 4.7GB to 17GB. Its shape and size is similar to CD but the difference in storage capacity is due to different chemical component and data is compressed before storing. It requires DVD drive for its operation. Read/write speed of DVD is slower than that of CD. Types of DVD are:
DVD-R
DVD-ROM
DVD-RW
DVD can also be classified as:
Single sided single layered DVD (4.7GB)
Single sided dual layered DVD (7-8GB)
Dual sided single layered DVD (9GB)
Dual sided dual layered DVD (17GB)
BD
It stands for Blue ray disk. It has the storage capacity of 25GB-50GB. It requires BD drive for its operation. Its shape and size is similar to CD and DVD. Types of BD are:
BD-R
BD-ROM
BD-RW
Working mechanism of CD
The surface of the CD contains land and pit. Land represents binary 1 and pit represents binary 0. During CD reading process a beam of light is emitted which strikes the surface of CD and gets reflected. The reflection is captured by lens in the CD drive. Difference in reflection from land and pit is identified to determine 1 and 0. Land is actually in a crystalline form and pit is in amorphous form. The size of land and pit is smaller in DVD compared to CD.
External memory devices:
• Zip disk
It is a magnetic memory. It is thee modification of floppy disk. It has the storage capacity of 100MB and 250MB. It requires Zip disk drive for its operation.

• Jaz disk
It is also a magnetic memory. It has the storage capacity of 2GB. It also requires separate Jaz disk drive for its operation.

• Super disk
It is also a magnetic memory. It has the storage capacity of 120MB. It requires Super disk drive for its operation. Both floppy and super disk can be used in super disk drive.

• Pen drive
It is a flash memory. It is a semi-conductor memory. It is mainly used for transferring data. It has faster read/write speed compared to magnetic memory. Pen drive has storage capacity of few MB-GB. A pen drive is a plug and play device. A pen drive can be connected with the computer through USB port.

4. What are output device? Explain in details.

Output Device
Those devices which are used to display result after processing in a human understandable language either in hardcopy form or softcopy form is known as output device. Example: Monitor, Printer, Plotter, Speaker and projector, etc.

Soft copy: The result or information which are not permanent and produce by using monitor, speaker, projector. It can be edited and deleted as required.
Monitor
It is also known as VDU (Visual Display Unit). It is the most basic output device. It is used to display the output. Types of monitor on the basis of color display are:

1. Monochrome monitor
It is a single colored monitor. It can display only text and images of a single color against a contrasting background. The first monitor displayed text and images of light green color against black background.
2. Gray scale monitor
It can display 256 different variations of black and white color. It can also display video. The first television set was gray scale.
3. Color monitor
It can display 16-42 million colors. It uses 3 basic colors Red, Blue and Green. All the other colors are the combination of these colors. Color monitor is also known as RGB monitor.
Types of monitor on the basis of architecture:
4. CRT Monitor
CRT is the large bulky sized monitor. It has high power requirement so it is not appropriate for portable devices. It is cheaper and has better brightness so, it is preferred by graphic designers.
Merits of CRT monitor are:
Ø It has better brightness.
Ø It is cheaper in cost.
Ø It is more durable.
Ø It has better graphics and larger viewing angle (~180)

De-merits of CRT monitor are:

Ø Due to its high brightness human eyes are negatively affected.
Ø It requires high power.
Ø It is large in size so occupies more space.
Ø It is not portable.
5. Flat panel monitor
a. LED
LED contains multiple small bulbs. The contents are displayed by turning the bulbs “on” and “off”. Initially it was used only for simple digital displays like in calculator, digital watch, etc. At present it is also used in television, desktop PC, laptop, etc.
Merits of LED are:
Ø It is light in weight so, it can be used in portable devices.
Ø It requires less power.
Ø It is small in size.
Ø Its viewing angle is larger compared to LCD.

De-merits of LED are:

Ø It has low brightness but is better than LCD and plasma.
Ø It is expensive compared to CRT.
Ø It is difficult to maintain.
b. LCD
LCD contains liquid crystals in between two plates of the screen. The plates are made by either glass or plastic. The front plate is transparent and the back plate is reflective. Liquid crystals are charged electronically to display the content. This monitor is popular for portable devices because of its small size, light weight, low power requirement however it has low brightness and it requires viewing angle of almost 90.
Merits of LCD:

Ø It is small in size.
Ø It is light in weight.
Ø It has low power requirements so, can be used in portable devices.
Ø It is cheaper than LED and plasma display.

De-merits of LCD:

Ø It has low brightness.
Ø It is expensive compared to CRT.
Ø It requires viewing angle of almost 90.

c. Plasma display
It contains neon gas in between the two plates of the screen in place of liquid crystals of LCD. It has larger viewing angle but is expensive than LCD. It is smaller in size, light in weight and it has low power requirement and low brightness.
Merits of plasma display:
Ø It is smaller in size and light in weight.
Ø It has low power requirement so can be used in portable devices.
Ø It has larger viewing angle.

De-merits of plasma display:

Ø It has low brightness.
Ø It is expensive than LCD.
Working mechanism of CRT:
A monochrome CRT contains single electron gun which emits beam of electrons. These electrons are attached towards positive phosphorous screen. When an electron strikes the screen it glows and emits light. A small area in which an electron strikes is known as pixel. To display a screen all the pixel are striked by electrons. Accelerating anode varies the speed of the electron and deflecting system changes the path of the electron.
A color CRT monitor contains three electron guns which emits three electrons at a time. These electrons converge in the same pixel to display a color.
Speaker:
Speaker is a soft copy output device for audio. It generates analog sound wave from stored digital sound by using vibrators. Different types of speakers vary on the loudness of sound generated. Some of the speakers used are:
• Ear phone
• Head phone
• Normal speaker
• Woofer
• Loud speaker
Hard copy output devices: The output device which are permanent and displays by printer and plotter. It can’t be altered and deleted.
• Printer
Printer makes the permanent impression of color on the printing material like paper, plastic, clothes, rubber, metal, etc. A printer can be single or multi-colored. Types of printer are:

Ø Impact printer
It prints by physically touching the printing material. It is noisier, slower for printing, single colored. It produces low quality output. It is usually cheaper and it can produce multiple copies at the same time by using carbon paper. It uses ink ribbon for printing.

Example:
• Dot matrix printer
• Daisy wheel printer
• Line printer
Dot matrix printer
• It is an impact type character printer. It prints character by the combination of dots where each dot is printed when the hammer strikes the printing material. It can print both image and text of different font and size. It is appropriate for low volume printing. It is usually available in three operating modes: fast, medium and slow. Faster speed will have low printing quality.
• Merits:
• It can print both image and text of different font and size.
• Its operating cost is low.
• It can print multiple copies at the same time using carbon paper.
•
• De-merits:
• It is noisy, slower.
• It has low printing quality.
• It can print single color only.
• It is not appropriate for large volume printing.
 Daisy wheel printer
• It is an impact type character printer. It can only print text of fixed size and font. It contains separate hammer for each character so it is also know as letter quality printer. Its printing quality is better than dot matrix printer. It is faster than dot matrix printer. It is rarely used at present.
• Merits:
• Its printing quality is better than dot matrix printer.
• It is faster than dot matrix printer.
• It can print multiple copies at the same time using carbon paper.
•
• De-merits:
• It can print text of fixed size and font.
• It is noisy, slower than non-impact printers.
• It has low printing quality than non-impact printers.
• It can print a single color.
• It is not appropriate for large volume printing.
• It can’t print images.
Non impact printer
it prints without touching the printing material. It sprays liquid or powder ink. It uses electromagnetic or electrostatic mechanism. It is noiseless, faster for printing usually expensive, it has high printing quality, it can be single or multi-colored, it cannot produce multiple copies at the same time.

Example: ink jet printer
It is non impact type character printer. It uses liquid ink for printing. It can be single or multi-colored. Multi-colored ink jet printer can use either RGB colors or CYMK (cyan, yellow, magenta, black). This printer uses dot-matrix approach for printing i.e. a dot is formed by spraying liquid ink. Series of dots are used tp print characters and images. It is cheaper to buy but its operating cost is expensive due to expensive ink. So, it is appropriate only for low volume printing.
Merits:
- It is not noisy and is faster than impact printers.
- It can be both single and multi-colored.
- It is cheaper to buy.
- It can print both text and images.
- Its printing quality is better than impact printers.

De-merits:
- Its operating cost is high.
-It is appropriate for low volume printing only.
- It can’t produce multiple copies at the same time.
-It is not appropriate for continuous printing.

laser printer
It is non-impact type page printer. It uses powder ink (toner) for printing. It is expensive to buy but its operating cost is low. So, it is appropriate for large volume printing. Multi-colored laser printer is larger in size and they are slower and expensive. It can print about 30 pages per minute.
Merits:
- It is not noisy and is faster than impact printer.
- It can be both single and multi-colored.
- Its operating cost is low.
-It can print both text and images.
- Its printing quality is better than impact printer.

De-merits:
v It is expensive to buy.
v It can’t print multiple copies at the same time.
It is not appropriate for continuous printing.

Thermal wax printer.
Printer can also be classified as:
Ø Character printer
Ø Line printer
Ø Page printer

• Plotter:
It is large sized printer. It is used to plot large maps, designs, advertisements, etc. It is multi-colored, slow for printing, expensive and large in size. Paper, plastic (mainly flex) is used as printing material. It uses technology like ink jet technology, color pen technology. Ink jet technology uses liquid ink whereas color pen technology uses multi colored pens controlled by the mechanical arm. Ink jet is cheaper and color pen has better printing quality. Different plotters in use are:
Ø Drum plotter
Ø Flat bed plotter

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