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SCANNERS

A scanner is a device that captures images from photographic prints, posters, magazine pages, and similar sources for computer editing and display. Scanners come in hand-held, feed-in, and flatbed types and for scanning black-and-white only, or color. 

 

HOW SCANNERS WORK
Scanners operate by shining light at the object or document being digitized and directing the reflected light (usually through a series of mirrors and lenses) onto a photosensitive element. In most scanners, the sensing medium is an electronic, light-sensing integrated circuit known as a charged coupled device (CCD). Light-sensitive photosites arrayed along the CCD convert levels of brightness into electronic signals that are then processed into a digital image.

A scanner consists of a flat transparent glass bed under which the CCD sensors, lamp, lenses, filters and also mirrors are fixed. The document has to be placed on the glass bed. There will also be a cover to close the scanner. This cover may either be white or black in colour. This colour helps in providing uniformity in the background. This uniformity will help the scanner software to determine the size of the document to be scanned.

The lamp brightens up the text to be scanned. Most scanners use a cold cathode fluorescent lamp (CCFL).

A stepper motor under the scanner moves the scanner head from one end to the other. The movement will be slow and is controlled by a belt. The scanner head consists of the mirrors, lens, CCD sensors and also the filter. The scan head moves parallel to the glass bed and that too in a constant path. As deviation may occur in its motion, a stabilizer bar will be provided to compromise it. The scan head moves from one end of the machine to the other. When it has reached the other end the scanning of the document has been completed. For some scanners, a two way scan is used in which the scan head has to reach its original position to ensure a complete scan.

As the scan head moves under the glass bed, the light from the lamp hits the document and is reflected back with the help of mirrors angled to one another. According to the design of the device there may be either 2-way mirrors or 3-way mirrors. The mirrors will be angled in such a way that the reflected image will be hitting a smaller surface. In the end, the image will reach a lens which passes it through a filter and causes the image to be focussed on CCD sensors. The CCD sensors convert the light to electrical signals according to its intensity. Take a look at the diagram given below.

The electrical signals will be converted into image format inside a computer. This reception may also differ according to the variation in the lens and filter design. A method called three pass scanning is commonly used in which each movement of the scan head from one end to another uses each composite colour to be passed between the lens and the CCD sensors. After the three composite colours are scanned, the scanner software assembles the three filtered images into one single -colour image.

Digitizer, stylus, Accelerometer and Gyroscope

 

A digitizer is a hardware device that receives analog information, such as sound or light, and records it digitally. Usually, the information is stored in a file on a computing device. This process is called digitization.

For example, a digital camera is a digitizer. Light enters through the camera lens, and the hardware and software inside the camera converts that information to binary data, and stores it an image file. The user may then transfer the file to a computer, where he or she can edit the image, print it out, or share it online.

Examples of digitizers

A digital camera is one example of a digitizer. Other examples include:

Audio digitizer

Most computers have a microphone jack, where you can connect an analog microphone. The analog input (the audio signal) is processed in the computer by a discrete sound card, or by audio hardware on the motherboard itself. This data can then be used by software running on the computer. Some audio digitizers are small hand-held devices, and some are expensive peripherals that provide professional-level conversion quality. The microphone in a smartphone is another audio digitizer.

Digital Tablet

A tablet is a computing device that is controlled with a finger or a digital pen called a stylus. A tablet is usually larger than a smartphone, but smaller than a computer monitor. Some tablets have a screen, which is touched directly, and some tablets are peripheral devices, without screens, which attach to a computer. The user can write, draw, and paint by touching the tablet. Software converts the analog touch input to lines or pressure-sensitive brush strokes in a document. The software may also perform handwriting recognition to convert handwritten text to typewritten words. When dealing with graphics these tablets are often referred to as a graphics tablet.

Accelerometer and gyroscope

Digitizers inside smartphones and tablet computers can detect how fast the device is moving (an accelerometer), and the angle it's held (a gyroscope). The analog information of motion and angular rotation is converted to data your apps can use in real time. For example, using a gyroscope, a smartphone could be held up to the sky to receive information about the position of stars and planets. The accelerometer helps reduce motion blur when you're taking a photo, and can trigger safety mechanisms if the device is accidentally dropped.

 

MAC Address

 A MAC (Media Access Control) address is a 48 bit unique ID assigned to every internet-connected machine that allows it to be identified when connected to a specific network. Also known as Hardware Address or physical address of machine on network.

A MAC address is a hardware identification number that uniquely identifies each device on a network. The MAC address is manufactured into every network card, such as an Ethernet card or Wi-Fi card, and therefore cannot be changed. 

MAC is divided into The vendor ID (24 bit) and other NIC identifier 24 bit.

Because there are millions of networkable devices in existence, and each device needs to have a unique MAC address, there must be a very wide range of possible addresses. For this reason, MAC addresses are made up of six two-digit hexadecimal numbers, separated by colons. For example, an Ethernet card may have a MAC address of 00:0d:83:b1:c0:8e. Fortunately, you do not need to know this address, since it is automatically recognized by most networks.

Finding Your MAC Address

windows

1. Click Start then Run (in Windows 7, Start and type in the Search Programs and Files box.)
2. Enter: cmd
3. Enter: ipconfig /all
   If the output scrolls off your screen, and it will on Vista and Windows 7, use: ipconfig /all | more
4. The Physical Address is your MAC address; it will look like 00-15-E9-2B-99-3C. You will have a physical address for each network connection that you have.

 Linux

Linux

1. Become root, using su.
2. Enter: ifconfig -a

   # ifconfig -a
   eth0      Link encap:Ethernet  HWaddr 00:09:3D:12:33:33  
             inet addr:10.248.155.17  Bcast:10.248.255.255  Mask:255.255.0.0
             inet6 addr: fe50::234:3dff:fe12:7d73/64 Scope:Link
             UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
             RX packets:3489041718 errors:0 dropped:0 overruns:0 frame:0
             TX packets:3259212142 errors:0 dropped:0 overruns:0 carrier:0
             collisions:0 txqueuelen:1000 
             RX bytes:2732221481 (2.5 GiB)  TX bytes:4065716672 (3.7 GiB)
             Interrupt:185

3. The ethernet devices are called eth0, eth1, and so on The MAC address is in the first line of the output, labeled HWaddr, it is 00:09:3D:12:33:33.

 

 

 

UNIX -- An INTRODUCTION

 

What Is UNIX?

UNIX is an operating system developed in the Bell Laboratories AT&T and is an example a multi-tasking, multi-user operating system. It provides its users with: program development tools; electronic communications facilities, such as an electronic mail; text editors and text formatters. There are also many development tools available as standard within the UNIX operating system that other operating systems require as add-ons.

UNIX is an operating system which was first developed in the 1960s, and has been under constant development ever since. By operating system, we mean the suite of programs which make the computer work. It is a stable, multi-user, multi-tasking system for servers, desktops and laptops.

UNIX systems also have a graphical user interface (GUI) similar to Microsoft Windows which provides an easy to use environment. However, knowledge of UNIX is required for operations which aren't covered by a graphical program, or for when there is no windows interface available, for example, in a telnet session.

Types of UNIX

There are many different versions of UNIX, although they share common similarities. The most popular varieties of UNIX are Sun Solaris, GNU/Linux, and MacOS X.

Operating System Notes Part 2 PDF

OS NOTES PART 5

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TYPES OF INTERNET CONNECTIONS

 DIAL UP CONNECTION: Dial-up Internet access is a form of Internet access that uses the facilities of the public switched telephone network (PSTN) to establish a connection to an Internet service provider (ISP) by dialing a telephone number on a conventional telephone line.
This type of connection is called dial-up because the initiating device, usually an Internet user's personal computer, will literally pick up the telephone line signal and dial up the telephone number of a receiving device, usually an Internet-connected modem.
The condition of the telephone line has a lot to do with the maximum speed of the dial up connection. Under optimal circumstances, a 56kbps throughput can be maintained. Real world speeds typically vary between 18kbps and 48kbps.

Broadband Connections:

The term broadband commonly refers to high-speed Internet access that is always on and faster than the traditional dial-up access. Broadband includes several high-speed transmission technologies such as:

• Digital Subscriber Line (DSL)
• Cable Modem
• Fiber
• Wireless
• Satellite
• Broadband over Powerlines (BPL)

The broadband technology you choose will depend on a number of factors. These may include whether you are located in an urban or rural area, how broadband Internet access is packaged with other services (such as voice telephone and home entertainment), price, and availability.

 

Digital Subscriber Line (DSL)

DSL is a wireline transmission technology that transmits data faster over traditional copper telephone lines already installed to homes and businesses. DSL-based broadband provides transmission speeds ranging from several hundred Kbps to millions of bits per second (Mbps). The availability and speed of your DSL service may depend on the distance from your home or business to the closest telephone company facility.

The following are types of DSL transmission technologies:

• Asymmetrical Digital Subscriber Line (ADSL) – Used primarily by residential customers, such as Internet surfers, who receive a lot of data but do not send much. ADSL typically provides faster speed in the downstream direction than the upstream direction. ADSL allows faster downstream data transmission over the same line used to provide voice service, without disrupting regular telephone calls on that line.
• Symmetrical Digital Subscriber Line (SDSL) – Used typically by businesses for services such as video conferencing, which need significant bandwidth both upstream and downstream.

Faster forms of DSL typically available to businesses include:

• High data rate Digital Subscriber Line (HDSL); and
• Very High data rate Digital Subscriber Line (VDSL).

Cable Modem

Cable modem service enables cable operators to provide broadband using the same coaxial cables that deliver pictures and sound to your TV set.

Most cable modems are external devices that have two connections: one to the cable wall outlet, the other to a computer. They provide transmission speeds of 1.5 Mbps or more.

Subscribers can access their cable modem service by simply turning on their computers, without dialing-up an ISP. You can still watch cable TV while using it. Transmission speeds vary depending on the type of cable modem, cable network, and traffic load. Speeds are comparable to DSL.

Fiber

• Fiber optic technology converts electrical signals carrying data to light and sends the light through transparent glass fibers about the diameter of a human hair. Fiber transmits data at speeds far exceeding current DSL or cable modem speeds, typically by tens or even hundreds of Mbps.
• The actual speed you experience will vary depending on a variety of factors, such as how close to your computer the service provider brings the fiber and how the service provider configures the service, including the amount of bandwidth used. The same fiber providing your broadband can also simultaneously deliver voice (VoIP) and video services, including video-on-demand.
• Telecommunications providers sometimes offer fiber broadband in limited areas and have announced plans to expand their fiber networks and offer bundled voice, Internet access, and video services.
• Variations of the technology run the fiber all the way to the customer’s home or business, to the curb outside, or to a location somewhere between the provider’s facilities and the customer.

Wireless

• Wireless broadband connects a home or business to the Internet using a radio link between the customer’s location and the service provider’s facility. Wireless broadband can be mobile or fixed.
• Wireless technologies using longer-range directional equipment provide broadband service in remote or sparsely populated areas where DSL or cable modem service would be costly to provide. Speeds are generally comparable to DSL and cable modem. An external antenna is usually required.
• Wireless broadband Internet access services offered over fixed networks allow consumers to access the Internet from a fixed point while stationary and often require a direct line-of-sight between the wireless transmitter and receiver. These services have been offered using both licensed spectrum and unlicensed devices. For example, thousands of small Wireless Internet Services Providers (WISPs) provide such wireless broadband at speeds of around one Mbps using unlicensed devices, often in rural areas not served by cable or wireline broadband networks.
• Wireless Local Area Networks (WLANs) provide wireless broadband access over shorter distances and are often used to extend the reach of a "last-mile" wireline or fixed wireless broadband connection within a home, building, or campus environment. Wi-Fi networks use unlicensed devices and can be designed for private access within a home or business, or be used for public Internet access at "hot spots" such as restaurants, coffee shops, hotels, airports, convention centers, and city parks.
• Mobile wireless broadband services are also becoming available from mobile telephone service providers and others. These services are generally appropriate for highly-mobile customers and require a special PC card with a built in antenna that plugs into a user’s laptop computer. Generally, they provide lower speeds, in the range of several hundred Kbps.

Satellite

Just as satellites orbiting the earth provide necessary links for telephone and television service, they can also provide links for broadband. Satellite broadband is another form of wireless broadband, and is also useful for serving remote or sparsely populated areas.

Downstream and upstream speeds for satellite broadband depend on several factors, including the provider and service package purchased, the consumer’s line of sight to the orbiting satellite, and the weather. Typically a consumer can expect to receive (download) at a speed of about 500 Kbps and send (upload) at a speed of about 80 Kbps. These speeds may be slower than DSL and cable modem, but they are about 10 times faster than the download speed with dial-up Internet access. Service can be disrupted in extreme weather conditions.

Broadband over Powerline (BPL)

BPL is the delivery of broadband over the existing low- and medium-voltage electric power distribution network. BPL speeds are comparable to DSL and cable modem speeds. BPL can be provided to homes using existing electrical connections and outlets. BPL is an emerging technology that is available in very limited areas. It has significant potential because power lines are installed virtually everywhere, alleviating the need to build new broadband facilities for every customer.

 

VSAT (Very Small Aperture Terminal)

 VSAT stands for “Very Small Aperture Terminal” and refers to receive/transmit terminals installed at dispersed sites connecting to a central hub via satellite using small diameter antenna dishes (.75 to 3.8 meter).
VSAT technology represents a cost effective solution for users seeking an independent communications network connecting a large number of geographically dispersed sites. VSAT networks offer value-added satellite-based services capable of supporting the Internet, LAN, voice/fax communications, video, security, and provide powerful, dependable private and public network communications solutions.
Generally, these systems operate in the Ku-band and C-band frequencies, and soon Ka-band. Ku-band based networks are used primarily in Europe and North America and utilize the smaller sizes of VSAT antennas. C-band, used extensively in Asia, Africa and Latin America, require larger antenna sizes. These are quite common in Cyber Cafes throughout the rest of the world.

VSAT networks can be configured to receive only or transmit and receive. Examples of uses we commonly see for receive only are:

• Stock market & other news broadcasting
• Training or continuing education from a distance
• Distribute financial trends & analyses
• Introduce new products at geographically dispersed locations
• Update market related data, news, and catalog prices
• Distribute video or TV programs (Directv and DISH)
• Distribute music in stores & public areas
• Relay advertising to electronic signs in retail stores.
Examples of uses we see for receive/transmit are:
• Interactive computer transactions
• Internet
• Distance Learning Video Teleconferencing
• Database inquiries
• Bank transactions, ATM
• Reservation systems
• Distributed remote process control and telemetry
• VoIP communications
• Airport flight and weather data
• Emergency services
• Electronic fund transfer at Point-of-Sale
• E-mail
• Medical data transfer
• Sales monitoring & stock control
• Surveillance and monitoring.
VSAT networks come in various shapes and sizes ranging from point-to-point, point-to-multipoint, and customized private hubs for thousands of sites. Mesh systems have traditionally been somewhat smaller in size than star systems—5 to 30 sites is a good rule of thumb.

Fundamentals Notes

 Generation of Computers, etc

Fundamentals Notes

Differences between Virtual Circuits and Datagram Networks

 

Differences between Virtual Circuits and Datagram Networks

 

Virtual Circuits	Datagram Networks
Virtual circuits are connection-oriented, which means that there is a reservation of resources like buffers, bandwidth, etc. for the time during which the newly setup VC is going to be used by a data transfer session.	It is connectionless service. There is no need for reservation of resources as there is no dedicated path for a connection session.
A virtual circuit network uses a fixed path for a particular session, after which it breaks the connection and another path has to be set up for the next the next session.	A Datagram based network is a true packet switched network. There is no fixed path for transmitting data.
All the packets follow the same path and hence a global header is required only for the first packet of connection and other packets will not require it.	Every packet is free to choose any path, and hence all the packets must be associated with a header containing information about the source and the upper layer data.
Packets reach in order to the destination as data follows the same path.	Data packets reach the destination in random order, which means they need not reach in the order in which they were sent out.
Virtual Circuits are highly reliable.	Datagram networks are not as reliable as Virtual Circuits.
Implementation of virtual circuits is costly as each time a new connection has to be set up with reservation of resources and extra information handling at routers.	But it is always easy and cost-efficient to implement datagram networks as there is no need of reserving resources and making a dedicated path each time an application has to communicate.

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