Monday, October 19, 2009

Communication and Network

Twisted - Pair



  • Least expensive and most widely used
  • Consists of two insulated copper wire arranged in a regular spiral patter, act as a single communication link
  • Used to transmit both analog and digital signals. Analog signals amplifiers are required about every 5 to 6 km. Digital signals, repeaters are required every 2 or 3 km.
  • Commonly used medium for in the telephone network.
  • Come in two varieties which are Unshielded Twisted Pair ( UTP ) Cable and Shielded Twisted Pair ( STP ) Cable.



  • Coaxial Cable


    • Contains thick, conductive metal wire at the center that is surrounded by meshed or braided metal shield along the same parallel axis.
    • Used for high-speed data transmission over distance of several kilometers.
    • Commonly used for radio antennae, cable TVs and LAN applications.
    • Can transmit signals greater distances and at a higher bandwidth.

  • Fiber - optic cable

    • Offers higher bandwidth and lower signal losses.
    • Allows higher data rates over longer distances.

  • Advantages of using :
  • Information carrying capacity – Fiber optic capacities are well in excess of that required by today’s network applications. If the wavelength is different, the actual bandwidth can rise up to 5Cbps.
  • Low signal loss – optical fibers offer low signal loss. It permits longer transmission distances. In comparison with copper, the longest recommended copper horizontal link is 100 meters; when using fiver it is 2000 meters or more.

  • Node



  • Client
  • Communicates only with server, not with other clients.
  • A standard PC that is running an operation system such as Windows 9x, Windows Me, Windows 2000 Professional, or Windows XP.
  • Windows contain the client software that enables the client computers to access the resources that servers share.
  • The connection in between the client and server is maintained only during the actual exchange of information.


  • Server

  • Refers to the various type of software that process the requests from a visitors to a website.

  • Used for running larger programs for multiple users often simultaneously and typically accessed only via a network.
  • Maintained and housed by the institution or organization that sets up the CMC.

  • Hub

  • Commonly used LAN connectivity devices ( although inexpensive switches are rapidly replacing hubs on networks)
  • Serve as a central connection points for LANS.
  • Contains no active electronics and therefore cannot be used to extend a LAN.
  • Organizes your cable and relays data signals to all the computers on the LAN.
  • Used on network that use twisted-pair cabling.
  • A new HUB can be attached to the current HUB, thus providing greater port density.


  • Network Interface Card ( NIC )

  • Hardware component that connects a station to the network medium.
  • An adapter that plugs into a computer, enabling it to connect to a local area network(LAN) for the purpose of communicating with other computers and devices.
  • Can be configured to improve the performance or security of data transfer between the station and the network.
  • To improve network security, a NIC can be configured to apply encryption to all messages before transmission.

    Network Operation system ( NOS )

  • Communicates with the PC hardware to make connection between the machines
  • Provides basic file and supervisory services over a network.
  • Provide a structure for access to application
  • Enable users to manipulate programs and data

    Host Computer


    Receive calls from other computer and stores information that can be retrieved.
    Computer that access the host computer are called remote computers.


    Network Manager

  • Provides one-stop shopping for all of your network configuration needs.
  • Usually considered someone who maintains an existing network, making sure it runs as smoothly as possible, making adjustments for new users and programs and solving problems.


Monday, October 12, 2009

Secondary Storage.

Disk Caching


Object caching is a mechanism used by SharePoint to cache site, page, and page layout properties. Disk caching is used to cache BLOBs so that they do not have to be retrieved from the database. Object and disk caching are extremely fast and can significantly improve performance of sites, especially when large media files are involved. By default, object caching is always on, and disk caching is turned off. In order to enable disk caching, you must edit the web.config file for the web application where you want to use it.

Redundant arrays of inexpensive disks ( RAID )


A redundant array of inexpensive (or redundant) disks is a storage solution that uses multiple disks that function together to provide reliable data recovery. RAID can prevent the loss of data and/or improve performance. It can be used to provide connectivity when an organization’s primary ISP’s service becomes unavailable. RAID provides several methods of writing data across multiple disks, and writing to several disks. Rather than losing a single disks and all the information, administrators can replace the damaged risks and regenerate the data quickly.

File Comprassion and Decompression


The programs used to perform the compression and decompressions of image files are called codecs (compression decompression software). Many of them are integral parts of the most popular file formats for moving images like JPEG, MPEG-2, MPEG-4 and QuickTime, and some can compress and decompress the information on the fly. Compression is about reducing the size of the file so that the transmission time is shorter and the storage requirements are smaller. Decompression is about bringing back the data to a format that can be viewed with standard software.


Input source file → Compression Algorithm → Output compressed file

Input compressed file → Decompression Algorithm → Output decomposed file

Monday, October 5, 2009

Input and Output

Magnetic Ink Character Recognition (MICR)

All banks use MICR for processing cheques. Along the bottom of a cheque the bank’s sort code, customer account number and cheque number are encoded in special characters in magnetic ink. The amount of the cheque is encoded in magnetic ink when it is handed in at a bank. The cheque can be processed extremely fast by high-speed MICR devices that read, sort and store the data on disk. MICR has several advantages for processing cheque :
• It is hard to forge the characters
• The characters can be read even if the cheque is crumpled, dirty or smudged
• The characters are readable by humans, unlike bar codes.


Optical-Character Recognition ( OCR )


Optical- character recognition (OCR) is a tool for converting pages of text into computer-readable form. It automates the tedious of key entry, one of the lest rewarding ways of interacting with computers.

• Optical character recognition (OCR) uses a scanner and special software.
• OCR allows individual characters (letters of the alphabet, numbers, punctuation marks, etc.) to be recognized.
• It is an idea method for getting lots of text into a word-processing or desktop publishing package without the need for re-typing.
• It is sometimes used for recognizing account numbers on bills.


Optical-mark recognition ( OMR )


An optical mark reader can detect marks made in preset positions on a form. It is widely used for marking multiple-choice exams and market research questionnaires.
• The hardware device used is called an optical mark reader.
• An optical mark reader can only read marks on specially designed documents.
• OMR is ideal for reading the data from questionnaires, answers to multiple-choice examination question, menu choices in hospitals, football pools and lottery tickets.


Dot-matrix printer



A dot matrix printer is an impact printer, producing its image by striking the paper through a ribbon. Its print head consists of a number of small pins, varying between 9 and 24 depending on the manufacturer. A 24pin print head will produce a better quality of print than a 9 pin print head because the dots are closer together. As the print head moves across the page, one or more pins strike the ribbon and make a dot on the paper.

Plotter



A plotter is an output device used to produce high quality line drawings such as building plans or electronic circuits. They are generally classified as pen ( vector plotters) or penless ( raster plotters). The former use pens to draw images using point-to-point data, moving the pen over the paper. Pen plotters are low in price and hold a large share of the plotter market. Penless plotters include electrostatic potters, thermal plotters and laser plotters. They are generally used where drawings of high densities are required.


Photo Printer


a photo printer is optimized to create high-quality photo prints, typically on special photo print paper. Most consumer photo printer use inkjet technology. However, photo printer are notoriously slow ( 5 minutes or more to make a single print) and drink ink like its Gatorade on a hot summer day. When you add up the cost of ink cartridge and the special photo paper you have to use, you will find that a single print will cost you ten cents or so, an average.

Portable Printer


Portable printers are small, lightweight printers that can be used on the go, such as with a notebook computer, handheld PC, or smart phone. Some portable need to be physically connected to the computer, others can receive documents to be printed via a wireless connection. Portable printers that can print on regular-sized (8.5 by 11 inch) paper are used by business people while travelling; portable receipt and barcode printers are used in some service professions.

Fax machine


A fax machine is an essential piece of equipment in many health care facilities. This machine transmits data or information electronically over the telephone lines. For the system to work the sending and receiving facilities must each have a fax machine and a telephone line designated for the fax machine.

Multi-functional device


Multi-Function Device is Hardware that combines several functions in one unit. An MFP (Multi Function Product/ Printer/ Peripheral), multifunctional, all-in-one (AIO), or Multifunction Device (MFD), is an office machine which incorporates the functionality of multiple devices in one, so as to have a smaller footprint in a home or small business setting (the SOHO market segment), or to provide centralized document management/distribution/production in a large-office setting.

Internet Telephones


Internet telephony converts your voice into data packets, similar to what the traditional phone company does when sending voice over fiber cables for long distances. At the far end , the dara packets are converted back into sound signals and the voice you hear.
Internet telephony = VoIP = digital phone conversations = less dependence on the traditional phone companies = savings and more features.