CHAPTER - 10 MANAGING A DATABASE

A database is a collection of information that is organized so that it can easily be accessed, managed, and updated. In one view, databases can be classified according to types of content: bibliographic, full-text, numeric, and images.

Within a computer's storage, data is a collection of numbers represented as bytes that are in turn composed of bits (binary digits) that can have the value one or zero. Data are processed by the CPU, which uses logical operations to produce new data(out) from source input.

Information is stimuli that has meaning in some context for its receiver. When information is entered into and stored in a computer, it is generally referred to as data. After processing (such as formatting and printing), output data can again be perceived as information.

Database software, often called a database management system (DBMS) allows users to :-

·       Create a computerized database

·       Add, modify and delete data

·       Sort and retrieve data

·       Create form and report form data

Data integrity identifies the quality of the data

Garbage in, garbage out (GIGO) points out the accuracy of a computer’s output depends on the accuracy of the input.

Valuable information should have following characterstic :-

• ·       Accurate
• ·       Verifiable
• ·       Timely
• ·       Organized
• ·       Accessibility
• ·       Useful
• ·       Cost effective

A character is one byte. Numbers, letters, space, punctuation marks, or other symbols.

A field is a combination of one or more related characters

• ·       Field name
• ·       Field size
• ·       Data type

4 layers of data hierarchy :-

• ·       Character
• ·       Field
• ·       Record
• ·       Files

A record is a group of related fields. A primary key uniquely identifies each record. When a record no longer is needed, a user deletes it from a file.

A data file is a collection of related records. A data dictionary contains data about each file in the database and each field in those files.

A query language consists of simple, English-like statements that allow users to specify the data to display, print, or store.

Query by example (QBE) provides a GUI to assist users with retrieving data.

A report generator allows users to design a report on the screen, retrieve data into the report design, and then display or print the report.

A DBMS provides means to ensure that only authorized users access data at permitted times. A DMBS provides a variety of technique to restore the database to a usable form in case it is damaged or destroyed :-

• ·       Backup
• ·       Log
• ·       Recovery utility
• ·       Continuous backup
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A data model consists of rules and standards that define how the database organizes data. A relational database stores data in tables that consist of rows and columns. A relationship is a link within the data

• ·       Each row has a primary key
• ·       Each column has a unique name

An object-oriented database (OODB) stores data in objects. Examples of applications appropriate for an object-oriented database include:-

• ·       Multimedia database
• ·       Groupware database
• ·       Computer aided database
• ·       Hypertext database

A multidimensional database can store data in more than two dimensions of data.

·       Sometimes known as a hypercube.

·       Can consolidate data much faster than a relational database.

A data warehouse is a huge database that stores and manages the data required to analyze historical and current transactions.

Databases on the web allow you to :-

• ·       Shop for product –amazon, ebay, zalora, 11 street
• ·       Buy and sell stock –Job street , Mudha
• ·       Object oriented – google map
• ·       Search for job
• ·       Make airline reservation- South Africa Airways
• ·       Register for college class
• ·       Check semester grades

Employees should learn how to use the data in the database effectively :-

·               Interact with database

·               Identify new data for the database

·               Maintain the database

CHAPTER-9 NETWORK AND COMMUNICATION

Computer communications describes a process in which two or more computers or devices transfer data, instructions, and information. Users can send and receive wireless messages using wireless messaging services. Mostly used for blog, chat room, Email, Fax.

  

Process of communication :-

·       Sending device

·       Communication channel

·       Receiving data

Wireless Internet access points allow people to connect wirelessly to the Internet from home, work, school, and in many public locations.

A Cybercafé is a coffeehouse, restaurant, or other location that provides personal computers with Internet access to its customers.

A global positioning system (GPS) is a navigation system that consists of one or more earth-based receivers that accept and analyze signals sent by satellites in order to determine the GPS receiver’s geographic location.

GPS receiver are available in :-

·       Built into mobile device

·       Available as handheld device

·       Available in new vehicles

A Network is a collection of computers and devices connected together via communications devices and transmission media

Advantages of a network include :-

·     Facilitaing communication

·     Sharing hardware

·     Sharing data and information

·     Sharing software

·     Transferring funds

A local area network (LAN) is a network that connects computers and devices in a limited geographical area.

A wireless LAN (WLAN) is a LAN that uses no physical wires.

A metropolitan area network (MAN) connects LANs in a metropolitan area.

A wide area network (WAN) is a network that covers a large geographic area.

The design of computers, devices, and media on a network is sometimes called the network architecture.

A network topology refers to the layout of the computers and devices in a communications network. Example – Ethernet , Token ring, Wi-Fi, Bluetooth, WAP.

Wi-Fi identifies any network based on the 802.11 standard that facilitates wireless communication. Sometimes referred to as wireless Ethernet.

Bluetooth defines how two Bluetooth devices use short-range radio waves to transmit data.

UWB (ultra-wideband) specifies how two UWB devices use short-range radio waves to communicate at high speeds.

IrDA transmits data wirelessly via infrared (IR) light waves.

RFID uses radio signals to communicate with a tag placed in or attached to an object, animal, or person.

Communications software consists of programs that are :-

• ·  Helps users establish a connection to another computer and network.
• ·          Manage the transmission of data , instructions, and information.
• ·           Provide an interface for users to communicate with one another.

A communications device is any type of hardware capable of transmitting data, instructions, and information between a sending device and a receiving device.

A dial-up modem converts signals between analog and digital.

A digital modem sends and receives data and information to and from a digital line.

A wireless modem uses the cell phone network to connect to the Internet wirelessly from a notebook computer, a smart phone, or other mobile device.

A network card enables a computer or device to access a network.

A router connects multiple computers or other routers together and transmits data to its correct destination on a network. Many are protected by a hardware firewall.

The amount of data that can travel over a communications channel sometimes is called the bandwidth.

Latency is the time it takes a signal to travel from one location to another on a network.

 Transmission media carries one or more signals.

Broadband media transmit multiple signals simultaneously.

Cellular radio is a form of broadcast radio that is used widely for mobile communications.

Microwaves are radio waves that provide a high-speed signal transmission.

A communications satellite is a space station that receives microwave signals from an earth-based station, amplifies it, and broadcasts the signal over a wide area.

CHAPTER-8 TYPES OF STORAGE

Storage holds data, instruction and information for future use . A storage medium is the physical material on which a computer keeps data, instruction and information . For example hardware, flash drive ,USB. A storage device is the computer hardware that records and retrieves items to and from storage media.

Capacity is the number of bytes a storage medium can hold.

Access time can be measured in two ways :-

• ·       The amount of time it takes a storage device to locate an item on a storage medium
• ·       The time required to deliver an item from memory to the processor

HARD DISK :-

A hard disk contains one or more inflexible, circular platters that use magnetic particles to store data, instructions , and information. Hard disks can store data using longitudinal recording or perpendicular recording.

Characteristic of  HARDWARE :-

·       Capacity

·       Platters

·       Read/Write

·       Cylinders

·       Sector and Tracks

·       Revolutions per minute

·       Transfer rate

·       Access Time

Formatting is the process of dividing the disk into tracks and sectors so that the operating system can store and locate data and information on the disk.

RAID (redundant array of independent disks) is a group of two or more integrated hard disks.

A network attached storage (NAS) device is a server connected to a network with the sole purpose of providing storage.

How Hard disk work ?

·                    Actuator that moves the read-write arm. In older hard drives, the actuators were stepper motors. In most modern hard drives, voice coils are used instead. As their name suggests, these are simple electromagnets, working rather like the moving coils that make sounds in loudspeakers. They position the read-write arm more quickly, precisely, and reliably than stepper motors and are less sensitive to problems such as temperature variations.

·                    Read-write arm swings read-write head back and forth across platter.

·                    Central spindle allows platter to rotate at high speed.

·                    Magnetic platter stores information in binary form.

·                    Plug connections link hard drive to circuit board in personal computer.

·                    Read-write head is a tiny magnet on the end of the read-write arm.

·                    Circuit board on underside controls the flow of data to and from the platter.

·                    Flexible connector carries data from circuit board to read-write head and platter.

·                    Small spindle allows read-write arm to swing across platter.

Memory card :-

A memory card is a removable flash memory device that you insert and remove from a slot in a computer, mobile device, or card reader/writer. For example – Flash card, Memory card , Micro SDHC , Memory stick , Micro SD, Compact flash.

USB flash drives plug into a USB port on a computer or mobile device.

An Express Card module is a removable device that fits in an Express Card slot. Developed by the PCMCIA. Commonly used in notebook computers.

Cloud storage is an Internet service that provides storage to computer users. Cloud storage is an Internet service that provides storage to computer users. Users subscribe to cloud storage for a variety of reasons :-

• ·       Access files from any computer
• ·       Store large files instantaneously
• ·       Allow others to access their files
• ·       View time – critical data and image immediately
• ·       Store offsite backups
• ·       Provide data center functions.

What is optical disk ?

An optical disc consists of a flat, round, portable disc made of metal, plastic, and lacquer that is written and read by a laser. Typically store software, data, digital photos, movies, and music. Read only vs. rewritable. Optical discs commonly store items in a single track that spirals from the center of the disc to the edge. Track is divided into evenly sized sectors.

Tape is a magnetically coated ribbon of plastic capable of storing large amounts of data and information. A tape drive reads and writes data and information on a tape

A magnetic stripe card contains a magnetic stripe that stores information.

A smart card stores data on a thin microprocessor embedded in the card.

CHAPTER-7 UNDERSTANDING OUTPUT

What is output ?

Output is data that has been processed into a useful form. An output device is any type of hardware component that conveys information to one or more people.

A display device visually conveys text, graphics, and video information. A monitor is packaged as a separate peripheral

• ·    LCD monitor - Liquid crystal display (LCD) uses a liquid compound to present information on a display device. LCD monitors use a digital signal and should plug into a DVI port, an HDMI port, or a Display Port. 
• ·       Widescreen - Televisions also are a good output device. Require a converter if you are connecting your computer to an analog television. Digital television (DTV) offers a crisper, higher-quality output. HDTV is the most advanced form of digital television
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Resolution is the number of horizontal and vertical pixels in a display device. A higher resolution uses a greater number of pixels.

 Plasma monitors are display devices that use gas plasma technology and offer screen sizes up to 150 inches

CRT - A CRT monitor is a desktop monitor that contains a cathode-ray tube.

A printer produces text and graphics on a physical medium. Printed information is called a hard copy, or printout landscape or portrait orientation.

How does laser printer work :-

Laser printers are a lot like photocopiers and use the same basic technology. Indeed, as we describe later in this article, the first laser printers were actually built from modified photocopiers. In a photocopier, a bright light is used to make an exact copy of a printed page. The light reflects off the page onto a light-sensitive drum; static electricity (the effect that makes a balloon stick to your clothes if you rub it a few times) makes ink particles stick to the drum; and the ink is then transferred to paper and "fused" to its surface by hot rollers. A laser printer works in almost exactly the same way, with one important difference: because there is no original page to copy, the laser has to write it out from scratch.

How does inkjet work :-

The information you store is in electronic format: each piece of data is stored electronically by a microscopically small switching device called a transistor. The printer's job is to convert this electronic data back into words and pictures: in effect, to turn electricity into ink. With an inkjet printer, it's easy to see how that happens: ink guns, operated electrically, fire precise streams of ink at the page. With a laser printer, things are slightly more complex. The electronic data from your computer is used to control a laser beam—and it's the laser that gets the ink on the page, using static electricity in a similar way to a photocopier.

An ink-jet printer forms characters and graphics by spraying tiny drops of liquid ink onto a piece of paper. Color or black-and-white. Printers with a higher dpi (dots per inch) produce a higher quality output.

A multifunction peripheral (MFP) is a single device that prints, scans, copies, and in some cases, faxes. Sometimes called an all-in-one device

A thermal printer generates images by pushing electrically heated pins against the heat-sensitive paper . For example – Thermal wax transfer printer.

An audio output device produces music, speech, or other sounds.

Headphones are speakers that cover or are placed outside of the ear

Earbuds (also called earphones) rest inside the ear canal.

A data projector is a device that takes the text and images displaying on a computer screen and projects them on a larger screen :-

• ·       LCD projector
• ·       Digital light processing (DLP) projector
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 Plotters are used to produce high-quality drawings.

Large-format printers create photo-realistic quality color prints on a larger scale.

Mobile printer :-

A mobile printer is a small, lightweight, battery-powered printer that allows a mobile user to print from a notebook computer, smart phone, or other mobile devices.

Label printer :-

A label printer is a small printer that prints on adhesive-type materials.

A postage printer prints postage stamps :-

Postage also can be printed on other types of printers.

How black and white laser printer work :-

·                      Millions of bytes (characters) of data stream into the printer from your computer.

      An electronic circuit in the printer (effectively, a small computer in its own right) figures out how to print this data so it looks correct on the page.
 
 
·        The electronic circuit activates the corona wire. This is a high-voltage wire that gives a static electric charge to anything nearby.
 
·        The corona wire charges up the photoreceptor drumso the drum gains a positive charge spread uniformly across its surface.
 
 
·        At the same time, the circuit activates the laser to make it draw the image of the page onto the drum. The laser beam doesn't actually move: it bounces off a moving mirror that scans it over the drum. Where the laser beam hits the drum, it erases the positive charge that was there and creates an area of negative charge instead. Gradually, an image of the entire page builds up on the drum: where the page should be white, there are areas with a positive charge; where the page should be black, there are areas of negative charge.
 
·        An ink roller touching the photoreceptor drum coats it with tiny particles of powdered ink (toner). The toner has been given a positive electrical charge, so it sticks to the parts of the photoreceptor drum that have a negative charge (remember that opposite electrical charges attract in the same way that opposite poles of a magnet attract). No ink is attracted to the parts of the drum that have a positive charge. An inked image of the page builds up on the drum.
 
 
·        A sheet of paper from a hopper on the other side of the printer feeds up toward the drum. As it moves along, the paper is given a strong positive electrical charge by another corona wire.
 
·        When the paper moves near the drum, its positive charge attracts the negatively charged toner particles away from the drum. The image is transferred from the drum onto the paper but, for the moment, the toner particles are just resting lightly on the paper's surface.
 
 
·        The inked paper passes through two hot rollers (the fuser unit). The heat and pressure from the rollers fuse the toner particles permanently into the fibers of the paper.
 
·        The printout emerges from the side of the copier. Thanks to the fuser unit, the paper is still warm. It's literally hot off the press.