Informatics Practices Class XI

CHAPTER 2 : SOFTWARE CONCEPTS 

Types of Software

Operating System:

The Operating System (OS) deals with all the basic functioning and the same is performed by the machines. For instance, showing the movement of the mouse on the screen when a person hovers the mouse. There are lots of Operating Systems available recently. The most popular and latest ones include the Windows XP, Mac, UNIX, Linux, Windows Vista, etc.

Functions of an Operating System

Need of an Operating System:

This is the same question we ask to the persons one of them knows English and the other ones knows Spanish so we need one person who is able to communicate between two same is the answer here for why we need the Operating System it is the communication pathway between the user of the machine and the machine where machine knows only machine language i.e. '1' and '0' on the other hand the man knows the alphabetic language. so operating system gets the alphabetic language from the user and change it to the machine understandable language and vice versa.

In earlier day's user had to design the application according to the internal structure of the hardware. Operating System was needed to enable the user to design the application without concerning the details of the computer's internal structure. In general the boundary between the hardware & software is transparent to the user.
1. Easy interaction between the human & computer. 

2. Starting computer operation automatically when power in turned on.

3. Loading & scheduling users program.

4. Controlling input & output.

5. Controlling program execution.

6. Managing use of main memory.

7. Providing security to users program.

For hardware functions such as input and output and memory allocation, the Operating System acts as an intermediary between application programs and the computer hardware, although the application code is usually executed directly by the hardware and will frequently call the OS or be interrupted by it.

Functions of an Operating System:

An operating system (OS) is a set of computer program that manages the hardware and software resources of a computer. At the foundation of all system software, the OS performs basic tasks such as controlling and allocating memory, prioritizing system requests, controlling input and output devices, facilitating networking, and managing files. It also may provide a graphical user interface for higher level functions. Various services performed by operating systems are discussed below.

Process management:

It deals with running multiple processes. Most operating system allows a process to be assigned a priority which affects its allocation of CPU time. Interactive operating systems also employ some level of feedback in which the task with which the user is working receives higher priority. In many systems there is a background process which runs when no other process is waiting for the CPU.

Memory management: 

The memory manager in an OS coordinates the memories by tracking which one is available, which is to be allocated or deallocated and how to swap between the main memory and secondary memories. The operating system tracks all memory used by each process so that when a process terminates, all memory used by that process will be available for other processes.

Disk and file systems:

Operating systems have a variety of native file systems that controls the creation, deletion, and access of files of data and programs.

Networking:

Most current operating systems are capable of using the TCP/IP networking protocols. This means that one system can appear on a network of the other and share resources such as files, printers, and scanners. Many operating systems also support one or more vendor-specific legacy networking protocols as well.

Security:

Most operating systems include some level of security.

Language Processor

Assembler: Assemblers create an object code by translating assembly instruction mnemonics into opcodes. They also determine symbolic names for memory locations as well as for other entities. A prime characteristic of assemblers is the use of symbolic references, which saves time consuming manual calculations and address updates after a program has been modified. The majority of assemblers also have macro facilities so that they can perform textual substitution, which means that they are able to create short sequences of instructions.
Compiler: A compiler is program that converts the instruction of a high level language into machine language as a whole. A program written in high level language is called source program. After the source program is converted into machine language by the compiler, it is called an object program.
The compiler checks each statement in the source program and generates machine instructions. Compiler also checks syntax errors in the program. A source program containing an error cannot be compiled into an object program.
A compiler can translate the programs of only that language for which it is written. For example C++ compiler can translate only those programs, which are written in C++. Each machine required a separate compiler for each high level language.

Interpreter: An interpreter is a program that converts one statement of a program at a time. It executes this statement before translating the next statement of the source program. If there is an error in the statement, the interpreter will stop working and displays an error message.
The advantage of interpreters over compilers is that an error is found immediately. So the programmer can make corrections during program development.

Utility Software:

Compression Tools:  Data compression can be used for many purposes on computers and achieved in many ways. There are two types of data compression, lossy and lossless. Lossy compression makes data smaller by removing excess data so that the end result is still acceptable for its purpose. This is a one-way process and the compressed data is the result. Lossless compression makes data smaller by looking for patterns that can be written more concisely. This is a reversible process and a compressed file is the result. This file will have to be decompressed to access the original data. Advantages of data compression are that compressed data will take up less space on a computer and be quicker to transmit

Data compression for computer files is a lossless compression
Data compression for audio can be lossy or lossless

Data compression of images can be either lossy or lossless depending on the compression format used.

Data compression of video is primarily lossy

Disk Defragmenter:

The process of defragmenting a computer disk consists of file-management methods to improve system stability. This procedure is generally used as part of various performance-improvement techniques within an operating system. The use of disk defragment software contains a list of benefits and setbacks users must consider before selecting an appropriate approach.

Antivirus: Antivirus software exists to protect computer users from viruses, worms and spyware. According to Symantec, the makers of Norton Antivirus, there are more than 1 million computer viruses. Because of the prevalence of the viruses, there are a lot of options for computer users in the area of antivirus software. Commonly used Antivirus are Norton, Kaspersky, Quick heal etc.

Application Software:

Application software is what allows users to store information, create content and media, access information and communicate. Because most of the processes of the world now run on computers, there are many types of software to handle all the functions that are required. All software applications have specific hardware requirements.

There are two types of Application software

General purpose Application Software e.g. Word, Excel, DBMS etc.

Specific Purpose Application Software e.g. Inventory Management System, Payroll System, Railway Reservation System, Hotel Management System etc.

Computer Security Threats:

Computer systems are vulnerable to many threats that can inflict various types of damage resulting in significant losses. This damage can range from errors harming database integrity to fires destroying entire computer centers. Losses can stem, for example, from the actions of supposedly trusted employees defrauding a system, from outside hackers, or from careless data entry clerks. Precision in estimating computer security-related losses is not possible because many losses are never discovered, and others are "swept under the carpet" to avoid unfavorable publicity. The effects of various threats varies considerably. Some affect the confidentiality or integrity of data while others affect the availability of a system.

Malware:

Short for "malicious software," Malware refers to software programs designed to damage or do other unwanted actions on a computer system. In Spanish, "mal" is a prefix that means "bad," making the term "badware," which is a good way to remember it (even if you're not Spanish).

Common examples of Malware include viruses, worms, Trojan horses, and Spyware. Viruses, for example, can cause havoc on a computer's hard drive by deleting files or directory information. Spyware can gather data from a user's system without the user knowing it. This can include anything from the Web pages a user visits to personal information, such as credit card numbers.

Virus :

Like a biological virus, a computer virus is something you don't want to get. Computer viruses are small programs or scripts that can negatively affect the health of your computer. These malicious little programs can create files, move files, erase files, consume your computer's memory, and cause your computer not to function correctly. Some viruses can duplicate themselves, attach themselves to programs, and travel across networks. In fact opening an infected e-mail attachment is the most common way to get a virus.

We all know it's hard enough to get a computer to work well when it is healthy, let alone when it has been attacked by a virus. Therefore, it is better to prevent an attack than to try and cure it. There are many antivirus programs available that scan incoming files for viruses before they can cause damage to your computer. Some of these programs include Norton Antivirus, McAfee Virus Scan, and Virex

Trojan Horse:

In Greek mythology, there is a story about the Trojan War. This war lasted many years, as the Greeks could not penetrate the heavily barricaded city of Troy. So one day, a few of the Greek soldiers brought the people of Troy a large wooden horse, which they accepted as a peace offering. The horse was moved inside the city walls, where it sat until the night. After the people of the city had fallen asleep, Greek soldiers jumped out of the wooden horse, opened the gates to let their fellow soldiers in, and took over the city.

So what is the moral of this story? Mainly, beware of Trojan horses. But how does that relate to computers? That's a good question. In the computing world, Trojan horses are more than just a myth. They really exist and can cause damage to your computer. Trojan horses are software programs that masquerade as regular programs, such as games, disk utilities, and even antivirus programs. But if they are run, these programs can do malicious things to your computer.

For example, a Trojan horse might appear to be a computer game, but once you double-click it, the program starts writing over certain parts of your hard drive, corrupting your data. While this is certainly something you want to avoid, it is good to know that these malicious programs are only dangerous if they are given a chance to run. Also, most antivirus programs can catch Trojan horses when scanning for viruses. Unlike viruses, however, Trojan horses don't replicate themselves. Though it is possible for a Trojan horse to be attached to a virus file that spreads to multiple computers.

Spyware:

As the name implies, this is software that "spies" on your computer. Nobody likes to be spied on, and your computer doesn't like it either. Spyware can capture information like Web browsing habits, e-mail messages, usernames and passwords, and credit card information. If left unchecked, the software can transmit this data to another person's computer over the Internet.

So how does Spyware get on your computer? Just like viruses, Spyware can be installed when you open an e-mail attachment containing the malicious software. It can also be installed when you install another program that has a Spyware installer attached to it. Because of the insidious nature of Spyware, most people don't even know when Spyware is on their computer. Fortunately, you can purchase anti-Spyware utilities that will search for Spyware on your computer and stomp the unwanted software out of your system.

Worm:

Just like regular worms tunnel through dirt and soil, computer worms tunnel through your computer's memory and hard drive. A computer worm is a type ofvirus that replicates itself, but does not alter any files on your machine. However, worms can still cause havoc by multiplying so many times that they take up your entire computer's available memory or hard disk space. If a worm consumes your memory, your computer will run very slowly and possibly even crash. If the worm affects your hard disk space, your computer will take a long time to access files and you will not be able to save or create new files until the worm has been eradicated.

Worms are hard to detect because they are typically invisible files. They often go unnoticed until your computer begins to slow down or starts having other problems. Unlike viruses and Trojan horses, worms can replicate themselves and travel between systems without any action from the user. For these reasons, it is good to have an antivirus program installed on your system that can detect and remove worms before they have a chance to replicate or spread to other computers. Security updates such as Windows Update also patch security holes that allow worms to infect your computer. So keep your security updates and virus definitions up-to-date and you should be able to keep your computer worm-free.

Virus detection and its removal:

Virus detection and its removal are made through an antivirus program which finds out viruses in a computer and then possibly removes or repairs the virus problem.Some of commonly used Virus detection and its removable tools are Norton Antivirus, McAfee, Virus Scan, Kaspersky and Quick Heal etc.

Digital Certificate:

A digital certificate is a pair of files on your computer that you can use to create the digital equivalent of handwritten signatures and sealed envelopes. Each pair of files is divided into two parts: the public key and the private key. The public key is the portion that is shared; the private key is the portion that you, and only you, should have access to. Your computer and programs understand how to share only the public portion of your keys so that others can see them, while still keeping your private keys secure.

For example, when sending an e-mail message, you can digitally sign the message by attaching your digital certificate. Once they receive the message, recipients can verify that it came from you by viewing the small attachment on the e-mail, which contains your public key information. This protects you from people who might try to "spoof" an e-mail that looks like it came from you but is really sent from a different e-mail account.

Digital Signature:

A digital signature authenticates electronic documents in a similar manner a handwritten signature authenticates printed documents. This signature cannot be forged and it asserts that a named person wrote or otherwise agreed to the document to which the signature is attached. The recipient of a digitally signed message can verify that the message originated from the person whose signature is attached to the document and that the message has not been altered either intentionally or accidentally since it was signed. Also, the signer of a document cannot later disown it by claiming that the signature was forged. In other words, digital signatures enable the “authentication” and “non-repudiation” of digital messages, assuring the recipient of a digital message of both the identity of the sender and the integrity of the message.

A digital signature is issued by a Certification Authority (CA) and is signed with the CA’s private key. A digital signature typically contains the: Owner’s public key, the Owner’s name, Expiration date of the public key, the Name of the issuer (the CA that issued the Digital ID), Serial number of the digital signature, and the digital signature of the issuer. Digital signatures deploy the Public Key Infrastructure (PKI) technology.

Cookies:

A "cookie" is a small piece of information sent by a web server to store on a web browser so it can later be read back from that browser. This is useful for having the browser remember some specific information. 

 An example is when a browser stores your passwords and user ID's. They are also used to store preferences of start pages, both Microsoft and Netscape use cookies to create personal start pages. Common cookies which companies use is find info are listed below: 

Online Ordering Systems

Site Personalization

Website Tracking

How Do They Work

A command line in the HTML of a document tell the browser to set a cookie of a certain name or value? Here is an example of some script used to set a cookie. Set-Cookie: NAME=VALUE; expir es=DATE; path=PATH; domain=DOMAIN_NAME; secure Cookies are usually run from CGI scripts, but they can also be set or read by JavaScript. 

Firewall:

A firewall protects networked computers from intentional hostile intrusion that could compromise confidentiality or result in data corruption or denial of service. It may be a hardware device or a software program (running on a secure host computer. In either case, it must have at least two network interfaces, one for the network it is intended to protect, and one for the network it is exposed to.

A firewall sits at the junction point or gateway between the two networks, usually a private network and a public network such as the Internet. The earliest firewalls were simply routers. The term firewall comes from the fact that by segmenting a network into different physical subnet works, they limited the damage that could spread from one subnet to another just like fire doors or firewalls.

Hardware Firewall

Hardware firewall providing protection to a Local Network.

Software Firewall:

Computer running firewall software to provide protection

A firewall examines all traffic routed between the two networks to see if it meets certain criteria. If it does, it is routed between the networks, otherwise it is stopped. A firewall filters both inbound and outbound traffic. It can also manage public access to private networked resources such as host applications. It can be used to log all attempts to enter the private network and trigger alarms when hostile or unauthorized entry is attempted. Firewalls can filter packets based on their source and destination addresses and port numbers. This is known as address filtering. Firewalls can also filter specific types of network traffic. This is also known as protocol filtering because the decision to forward or reject traffic is dependant upon the protocol used, for example HTTP, ftp or telnet. Firewalls can also filter traffic by packet attribute or state.

Password:

A password is an un-spaced sequence of characters used to determine that a computer user requesting access to a computer system is really that particular user. Typically, users of a multi-user or securely protected single-user system claim a unique name (often called a user ID) that can be generally known. In order to verify that someone entering that user ID really is that person, a second identification, the password, known only to that person and to the system itself, is entered by the user. A password is typically somewhere between four and 16 characters, depending on how the computer system is set up. When a password is entered, the computer system is careful not to display the characters on the display screen, in case others might see it.

  

File Access Permission:

File access permission means how to restrict the access to file or folder e.g.

  

File and Folder Permissions Used by Windows

Permission	Meaning for Folders	Meaning for Files
Read	Permits viewing and listing of files and subfolders	Permits viewing or accessing of the file's contents
Write	Permits adding of files and subfolders	Permits writing to a file
Read & Execute	Permits viewing and listing of files and subfolders as well as executing of files; inherited by files and folders	Permits viewing and accessing of the file's contents as well as executing of the file
List Folder Contents	Permits viewing and listing of files and subfolders as well as executing of files; inherited by folders only	N/A
Modify	Permits reading and writing of files and subfolders; allows deletion of the folder	Permits reading and writing of the file; allows deletion of the file
Full Control	Permits reading, writing, changing, and deleting of files and subfolders	Permits reading, writing, changing and deleting of the file

CHAPTER 1 

HARDWARE CONCEPTS 

BASIC COMPUTER OPERATIONS

A computer as shown below performs basically five major operations or functions irrespective of their size and make. These are 1) it accepts data or instructions by way of input, 2) it stores data, 3) it can process data as required by the user, 4) it gives results in the form of output, and 5) it controls all operations inside a computer. We discuss below each of these operations.

1. Input: This is the process of entering data and programs in to the computer system. You should know that computer is an electronic machine like any other machine which takes as inputs raw data and performs some processing giving out processed data. Therefore, the input unit takes data from us to the computer in an organized manner for processing.

2. Storage: The process of saving data and instructions permanently is known as storage. Data has to be fed into the system before the actual processing starts. It is because the processing speed of Central Processing Unit (CPU) is so fast that the data has to be provided to CPU with the same speed. Therefore the data is first stored in the storage unit for faster access and processing. This storage unit or the primary storage of the computer system is designed to do the above functionality. It provides space for storing data and instructions.

The storage unit performs the following major functions: All data and instructions are stored here before and after processing.Intermediate results of processing are also stored here.

3. Processing: The task of performing operations like arithmetic and logical operations is called processing. The Central Processing Unit (CPU) takes data and instructions from the storage unit and makes all sorts of calculations based on the instructions given and the type of data provided. It is then sent back to the storage unit.

4. Output: This is the process of producing results from the data for getting useful information. Similarly the output produced by the computer after processing must also be kept somewhere inside the computer before being given to you in human readable form. Again the output is also stored inside the computer for further processing.

5. Control: The manner how instructions are executed and the above operations are performed. Controlling of all operations like input, processing and output are performed by control unit. It takes care of step by step processing of all operations in side the computer.

Arithmetic Logical Unit (ALU)

After you enter data through the input device it is stored in the primary storage unit. The actual processing of the data and instruction are performed by Arithmetic Logical Unit. The major operations performed by the ALU are addition, subtraction, multiplication, division, logic and comparison. Data is transferred to ALU from storage unit when required. After processing the output is returned back to storage unit for further processing or getting stored.

Control Unit (CU)

The next component of computer is the Control Unit, which acts like the supervisor seeing that things are done in proper fashion. The control unit determines the sequence in which computer programs and instructions are executed. Things like processing of programs stored in the main memory, interpretation of the instructions and issuing of signals for other units of the computer to execute them. It also acts as a switch board operator when several users access the computer simultaneously. Thereby it coordinates the activities of computer’s peripheral equipment as they perform the input and output. Therefore it is the manager of all operations mentioned in the previous section.

Central Processing Unit (CPU)

The ALU and the CU of a computer system are jointly known as the central processing unit. You may call CPU as the brain of any computer system. It is just like brain that takes all major decisions, makes all sorts of calculations and directs different parts of the computer functions by activating and controlling the operations.

       

      HARDWARE                        SOFTWARE

Personal Computer Configuration

Now let us identify the physical components that make the computer work. These are

1. Central Processing Unit (CPU) 2. Computer Memory (RAM and ROM) 3. Data bus  4. Ports 5. Motherboard 6. Hard disk 7. Output Devices 8. Input Devices 

All these components are inter-connected for the personal computer to work.

Memory

There are two kinds of computer  memory: primary and secondary. Primary memory is accessible directly by the processing unit. RAM is an example of primary memory. As soon as the computer is switched off the contents of the primary memory is lost. You can store and retrieve data much faster with primary memory compared to secondary memory. Secondary memory such as floppy disks, magnetic disk, etc., is located outside the computer. Primary memory is more expensive than secondary memory. Because ofthis the size of primary memory is less than that of secondary memory.

Random Access Memory (RAM): The primary storage is referred to as random access memory (RAM) because it is possible to randomly select and use any location of the memory directly store and retrieve data. It takes same time to any address of the memory as the first address. It is also called read/write memory. The storage of data and instructions inside the primary storage is temporary. It disappears from RAM as soon as the power to the computer is switched off. The memories, which loose their content on failure of power supply, are known as volatile memories .So now we can say that RAM is volatile memory.

 Read Only Memory (ROM): There is another memory in computer, which is called Read Only Memory (ROM). Again it is the ICs inside the PC that form the ROM. The storage of program and data in the ROM is permanent. The ROM stores some standard processing programs supplied by the manufacturers to operate the personal computer. The ROM can only be read by the CPU but it cannot be changed. The basic input/output program is stored in the ROM that examines and initializes various equipment attached to the PC when the switch is made ON. The memories, which do not loose their content on failure of power supply.

Input Devices

Input devices are necessary to convert our information or data in to a form which can be understood by the computer. A good input device should provide timely, accurate and useful data to the main memory of the computer for processing followings are the most useful input devices.

Keyboard: - This is the standard input device attached to all computers. The layout of keyboard is just like the traditional typewriter of the type QWERTY. It also contains some extra command keys and function keys. It contains a total of 101 to 104 keys.. You have to press correct combination of keys to input data. The computer can recognise the electrical signals corresponding to the correct key combination and processing is done accordingly.

Mouse: - Mouse is an input device ,that is used with your personal computer. It rolls on a small ball and has two or three buttons on the top. When you roll the mouse across a flat surface the screen censors the mouse in the direction of mouse movement. The cursor moves very fast with mouse giving you more freedom to work in any direction. It is easier and faster to move through a mouse.

 Scanner: The keyboard can input only text through keys provided in it. If we want to input a picture the keyboard cannot do that. Scanner is an optical device that can input any graphical matter and display it back. The common optical scanner devices are Magnetic Ink Character Recognition (MICR), Optical Mark Reader (OMR) and Optical Character Reader (OCR).

 Optical Character Recognition (OCR): - This technique unites the direct reading of any printed character. Suppose you have a set of hand written characters on a piece of paper. You put it inside the scanner of the computer. This pattern is compared with a site of patterns stored inside the computer. Whichever pattern is matched is called a character read. Patterns that cannot be identified are rejected. OCRs are expensive though better the MICR.

 Smart Card Reader: Smart Card Readers are also known as card programmers (because they can write to a card), card terminals, card acceptance device (CAD), or an interface device (IFD). There is a slight difference between the card reader and the terminal. The term ‘reader’ is generally used to describe a unit that interfaces with a PC for the majority of its processing requirements. In contrast, a ‘terminal’ is a self-contained processing device. Smart cards are portable data cards that must communicate with another device to gain access to a display device or a network. Cards can be plugged into a reader commonly referred to as a card terminal, or they can operate with radio frequencies (RF). When the smart card and the card reader come in contact, each identifies itself to the other by sending and receiving information. If the messages exchanged do not match, no further processing takes place. So, unlike ordinary bank cards, smart cards can defend themselves against unauthorized users and uses in innovative security measures.

Barcode Reader: A barcode reader, also called a price scanner or point-of-sale scanner, is a hand-held or stationary input device used to capture and read information contained in a bar code. A barcode reader consists of a scanner, a decoder (either built-in or external), and a cable used to connect the reader with a computer. Because a barcode reader merely captures and translates the barcode into numbers and/or letters, the data must be sent to a computer so that a software application can make sense of the data. Barcode scanners can be connected to a computer through a serial port, keyboard port, or an interface device called a wedge. A barcode reader works by directing a beam of light across the bar code and measuring the amount of light that is reflected back. (The dark bars on a barcode reflect less light than the white spaces between them.) The scanner converts the light energy into electrical energy, which is then converted into data by the decoder and forwarded to a computer.

There are five basic kinds of barcode readers -- pen wands, slot scanners, Charge-Couple Device ( CCD ) scanners, image scanners, and laser scanners.

Biometric Sensor: Biometric sensors/detectors are useful in several industries as well as consumers who can put them to use in access control and identity access management and information technology applications. Sensors and detectors are semiconductors (meaning its electric conductivity is in between a conductor and an insulator) which use algorithms to process images from the user's physical characteristics.

Biometric sensors work by producing electrical currents when they scan a user's physical characteristic. Many physical characteristics may be scanned by a biometric sensor including eyes, fingerprints, or DNA. Sensors contain an analog to digital converter enabling it to digitize the image and store the digital information in memory so that it can verify the user next time he or she needs to authenticate their identity.

 Web Camera:-A web camera (or webcam) is a real time camera whose images can be accessed using the World Wide Web, instant messaging, or a PC video calling application. Generally, a digital camera delivers images to a web server, either continuously or at regular intervals.A webcam is also the name of a class of video camera devices which connect directly to the PC for the purpose of video calling over the internet.The first webcam was pointed at the Trojan room coffee pot in the computer science department of Cambridge University. This webcam is now defunct, as it was finally switched off on 22 August 2001

Initially intended for personal videoconferencing, it was quickly realised that World Wide Web users enjoyed viewing images from cameras set up by others elsewhere in the world. While webcam refers to the technology generally, the "Web" part is often replaced with the "Category" of images the camera provides. Today there are thousands of webcam that provide views into homes, offices and other buildings as well as providing panoramic views of cities (Metrocams) and the countryside. Images from satellites are frequently posted on the World Wide Web. Webcams are also used to monitor traffic with TraffiCams, the weather with WeatherCams and even volcanos with VolcanoCams.

Visual Display Unit: The most popular input/output device is the Visual Display Unit (VDU). It is also called the monitor. A Keyboard is used to input data and Monitor is used to display the input data and to receive massages from the computer. A monitor has its own box which is separated from the main computer system and is connected to the computer by cable. In some systems it is compact with the system unit. It can be color or monochrome.

Terminals: It is a very popular interactive input-output unit. It can be divided into two types: hard copy terminals and soft copy terminals. A hard copy terminal provides a printout on paper whereas soft copy terminals provide visual copy on monitor. A terminal when connected to a CPU sends instructions directly to the computer. Terminals are also classified as dumb terminals or intelligent terminals depending upon the work situation.

Printer: It is an important output device which can be used to get a printed copy of the processed text or result on paper. There are different types of printers that are designed for different types of applications.

Depending on their speed and approach of printing, printers are classified as impact and non-impact printers.

Impact printers: use the familiar typewriter approach of hammering a typeface against the paper and inked ribbon. Dot-matrix printers are of this type.

Non-impact printers: do not hit or impact a ribbon to print. They use electro-static chemicals and ink-jet technologies. Laser printers and Ink-jet printers are of this type. This type of printers can produce color printing and elaborate graphics.

Ink-jet (bubble-jets) printers: Ink-jets(bubble-jets) printers spray ionized tiny drops of ink onto a page to create an image.  This is achieved by using magnetized plates which direct the ink's path onto the paper in the desired pattern. Almost all ink-jets offer a color option as standard, in varying degrees of resolution. 

Laser Printers: Laser printers operate by shining a laser beam to produce an image on a drum. The drum is then rolled through a pool, or reservoir, or toner, and the electrically charged portions of the drum pick up ink. Finally, using a combination of heat and pressure, the ink on the drum is transferred onto the page. Laser printers print  very fast, and the supply cartridges work a long time. Color laser printers use the same toner-based printing process as black and white ( B/W) laser printers, except that they combine four different toner colors.

Plotters: Plotters are large-scale printers that are very accurate at reproducing line drawings. They are commonly used for technical drawings such as engineering drawings or architectural blueprints. The two basic types of plotters are called flatbed plotters and drum plotters. Flatbed plotters are horizontally aligned with a flat surface to which a piece of paper is attached. The paper remains stationary and the printer moves pens across the paper to draw the image. Drum plotters, also called upright plotters, are vertically positioned. They have a drum that the paper rolls on. Drum plotters usually make more noise and are more compact than flatbed plotters.

Secondary Storage Device: Alternatively referred to as external memory and auxiliary storage, secondary storage is a storage medium that holds information until it is deleted or overwritten regardless if the computer has power. For example, a floppy disk drive and hard disk drive are both good examples of secondary storage devices.

Magnetic Tapes: The Magnetic Tapes is the Type of Secondary Storage Device and this Device is used for taking back up of data and this Tape contains some magnetic fields and the Magnetic Tapes are used Accessing the data into the Sequential Form and the Tape Also Contains a Ribbon which is coated on the Single Side of the Tape and also contains a head which reads the data which is Recorded on to the Tape. And when we are reading the information from the disk then we can also read backward information means we can also back the Tape for Reading the Previous information. And For inserting the Tape into the System we also Requires Some Tape Drives Which Contains Tape and which is Responsible for Reading the contents from the Tapes. They can Store huge Amount of data into the Tape Drive , But the Main Limitation of the Tape Drive is that we cant Access the Data from the Disks directly means if we wants to 100th Record from the Tape then we must have to move all the Previous i.e. 99th Records first. And the Tapes are also easily damaged due to the Human Errors.

Magnetic Disks : - This is also called as the hard disk and this is made from the thin metal platter which is coated on the both sides of the magnetic Disks. And the there are Many Plates or Platters into a single hard disk and all the Plates are Made from the Magnetic Materials and all the Disks are Rotate from the 700 to 3600 rpm means Rotation per Minute and the hard disk also Contains a head which is used for both Reading and Writing the Data from the Hard Disks.

The Plate of Disk is Divided into the Tracks and sectors and the collection of Tracks makes a Cylinder means all the Tracks of the Disk which a Consecutive Areas makes a Cylinder.

Floppy Diskette: Floppy disk is a kind of storage device that can be used to  carried around? The Floppy Disk is also a Secondary Storage device which is used for storing the data in a Permanent Manner. The floppy is made up of Rigid Mylar Plastic and also contains a Magnetic black disk inside the Plastic Cover. The Floppy Disk also Stores all the Data into the Form of Tracks and Sectors and the floppy Disk provides both Reading and Writing the data into the Disk. The Floppy Disk is also called as Reusable Disk means the Floppy Disk Provides us the Facility to Read and Writes the Data into disk as and When Necessary and Also Many Times. We can Read and Write the data from the Disk.

 

DVD: DVD stands for Digital Versatile/Video Disc, DVDR stands for DVD Recordable and DVDRW for DVD Re-Writeable. If you're familiar with regular audio/music CDs or regular DVD-Video discs, then you will know what a recordable DVD looks like. A recordable DVD stores up to 2 hours of very good quality DVD-Video, including several audio tracks in formats like stereo, Dolby Digital or DTS and also advanced menu systems, subtitles and still pictures that can be played by many standalone DVD Players and most computer DVD-ROMs. If you choose to lower the video quality it is possible to store several hours video on a recordable DVD using low bit rates and low resolution with video quality more like VHS, SVHS, SVCD, CVD or VCD. It is also possible to have up to 4.37 GB ordinary data or mix DVD-Video and data on a recordable DVD that can be played by most computer DVD-ROMs. 

 

USB Drives: USB Drives USB drives are known by a myriad of names, including thumb drives (since the most common size is that of your thumb), jump drives and flash drives. USB drives are currently available in USB 2.0 with USB 3.0 hitting the market now. These small plug-and-play drives are removable, re-writable, and great for storing personal and professional data, as many are hardware-encrypted devices for ultimate security.

 

Memory Card:  A memory card (sometimes called a flash memory card or a storage card) is a small storage medium used to store data such as text, pictures, audio, and video, for use on small, portable or remote computing devices. Most of the current products use flash memory, although other technologies are being developed. There are a number of memory cards on the market, including the SD card (secure digital card), the CF card (Compact Flash card), the Smart Media card, the Memory Stick, and the Multimedia Card.

MEMORY UNITS