Input and Output Devices, Computer Data Storage and Operating Systems: An Overview - Prof., Study notes of Sociology of Work and Employment

Download Input and Output Devices, Computer Data Storage and Operating Systems: An Overview - Prof. and more Study notes Sociology of Work and Employment in PDF only on Docsity! Computer Literacy – Communications Information OTS 251/D 1. The Universal System Model1 2. Input Devices2 Input device - From Wikipedia, the free encyclopedia An input device is any peripheral (piece of computer hardware equipment) used to provide data and control signals to an information processing system (such as a computer). Input and output devices make up the hardware interface between a computer as a scanner or 6DOF controller. TERI MA DI Early devices ▪ Unit record equipment ▪ Punched card Keyboards A keyboard is a human interface device, which is represented as a layout of buttons. Each button, or key, can be used to either input a linguistic character to a computer, or to call upon a particular function of the computer. Traditional keyboards use spring-based buttons, though newer variations employ virtual keys, or even projected keyboards. Examples of types of keyboards include: ▪ Computer keyboard ▪ Keyer ▪ Chorded keyboard ▪ LPFK Pointing devices A computer mouse 1 http://www.scribd.com/doc/2083190/Universal-Systems-Model 2 http://en.wikipedia.org/wiki/Input_device Page 1 of 24 Computer Literacy – Communications Information OTS 251/D A pointing device is any human interface device that allows a user to input spatial data to a computer. In the case of mice and touch screens, this is usually achieved by detecting movement across a physical surface. Analog devices, such as 3D mice, joysticks, or pointing sticks, function by reporting their angle of deflection. Movements of the pointing device are echoed on the screen by movements of the cursor, creating a simple, intuitive way to navigate a computer's GUI. High-degree of freedom input devices Some devices allow many continuous degrees of freedom as input. These can be used as pointing devices, but are generally used in ways that don't involve pointing to a location in space, such as the control of a camera angle while in 3D applications. These kinds of devices are typically used in CAVEs, where input may register 6DOF. Composite devices Imaging and Video input devices Video input devices are used to digitize images or video from the outside world into the computer. The information can be stored in a multitude of formats depending on the user's requirement. ▪ Webcam ▪ Image scanner ▪ Fingerprint scanner ▪ Barcode reader ▪ 3D scanner ▪ Laser rangefinder Medical Imaging ▪ Computed tomography ▪ Magnetic resonance imaging ▪ Positron emission tomography ▪ Medical ultrasonography Audio input devices In the fashion of video devices, audio devices are used to either capture or create sound. In some cases, an audio output device can be used as an input device, in order to capture produced sound, and then you can play it back ▪ Microphone ▪ MIDI keyboard or other digital musical instrument ▪ Instrument to Computer cords, such as the Stealth Plug for the guitar 3. Output Devices3 An output device is any piece of computer hardware equipment used to communicate the results of data processing carried out by an information processing system (such as a computer) to the outside world. In computing, input/output, or I/O, refers to the communication between an information processing system (such as a computer) and the outside world. Inputs are the signals or data sent to the system, and outputs are the signals or data sent by the 3 http://en.wikipedia.org/wiki/Output_device Page 2 of 24 Computer Literacy – Communications Information OTS 251/D used to bootstrap the computer, that is, to read a larger program from non-volatile secondary storage to RAM and start to execute it. A non-volatile technology used for this purpose is called ROM, for read-only memory (the terminology may be somewhat confusing as most ROM types are also capable of random access). Many types of "ROM" are not literally read only, as updates are possible; however it is slow and memory must be erased in large portions before it can be re-written. Some embedded systems run programs directly from ROM (or similar), because such programs are rarely changed. Standard computers do not store non-rudimentary programs in ROM, rather use large capacities of secondary storage, which is non-volatile as well, and not as costly. Secondary storage A hard disk drive with protective cover removed. Secondary storage, in popular usage, differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage. Secondary storage does not lose the data when the device is powered down—it is non-volatile. Per unit, it is typically also an order of magnitude less expensive than primary storage. Consequently, modern computer systems typically have an order of magnitude more secondary storage than primary storage and data is kept for a longer time there. In modern computers, hard disk drives are usually used as secondary storage. The time taken to access a given byte of information stored on a hard disk is typically a few thousandths of a second, or milliseconds. By contrast, the time taken to access a given byte of information stored Page 5 of 24 Computer Literacy – Communications Information OTS 251/D in random access memory is measured in billionths of a second, or nanoseconds. This illustrates the very significant access-time difference, which distinguishes solid-state memory from rotating magnetic storage devices: hard disks are typically about a million times slower than memory. Rotating optical storage devices, such as CD and DVD drives, have even longer access times. Some other examples of secondary storage technologies are: flash memory (e.g. USB flash drives or keys), floppy disks, magnetic tape, paper tape, punched cards, standalone RAM disks, and Iomega Zip drives. The secondary storage is often formatted according to a file system format, which provides the abstraction necessary to organize data into files and directories, providing also additional information (called metadata) describing the owner of a certain file, the access time, the access permissions, and other information. Most computer operating systems use the concept of virtual memory, allowing utilization of more primary storage capacity than is physically available in the system. As the primary memory fills up, the system moves the least-used chunks (pages) to secondary storage devices (to a swap file or page file), retrieving them later when they are needed. As more of these retrievals from slower secondary storage are necessary, the more the overall system performance is degraded. Tertiary storage Large tape library. Tape cartridges placed on shelves in the front, robotic arm moving in the back. Visible height of the library is about 180 cm. Tertiary storage or tertiary memory,[1] provides a third level of storage. Typically it involves a robotic mechanism which will mount (insert) and dismount removable mass storage media into a storage device according to the system's demands; this data is often copied to secondary storage before use. It is primarily used for archival of rarely accessed information since it is much slower than secondary storage (e.g. 5–60 seconds vs. 1-10 milliseconds). This is primarily useful for extraordinarily large data stores, accessed without human operators. Typical examples include tape libraries and optical jukeboxes. When a computer needs to read information from the tertiary storage, it will first consult a catalog database to determine which tape or disc contains the information. Next, the computer will instruct a robotic arm to fetch the medium and place it in a drive. When the computer has finished reading the information, the robotic arm will return the medium to its place in the library. Off-line storage Off-line storage, also known as disconnected storage, is a computer data storage on a medium or a device that is not under the control of a processing unit.[2] The medium is recorded, usually in a secondary or tertiary storage device, and then physically removed or disconnected. It must be inserted or connected by a human operator before a computer can access it again. Unlike tertiary storage, it cannot be accessed without human interaction. Off-line storage is used to transfer information, since the detached medium can be easily physically transported. Additionally, in case a disaster, for example a fire, destroys the original data, a medium in a remote location will be probably unaffected, enabling disaster recovery. Off- Page 6 of 24 Computer Literacy – Communications Information OTS 251/D line storage increases general information security, since it is physically inaccessible from a computer, and data confidentiality or integrity cannot be affected by computer-based attack techniques. Also, if the information stored for archival purposes is accessed seldom or never, off-line storage is less expensive than tertiary storage. In modern personal computers, most secondary and tertiary storage media are also used for off- line storage. Optical discs and flash memory devices are most popular, and to much lesser extent removable hard disk drives. In enterprise uses, magnetic tape is predominant. Older examples are floppy disks, Zip disks, or punched cards. 5. Adaptive Technologies for users with disabilities in the workplace. http://www.makoa.org/computers.htm#guide 6. Function of Operating Systems What is an Operating System The operating system is the core software component of your computer. It performs many functions and is, in very basic terms, an interface between your computer and the outside world. In the section about hardware, a computer is described as consisting of several component parts including your monitor, keyboard, mouse, and other parts. The operating system provides an interface to these parts using what is referred to as "drivers". This is why sometimes when you install a new printer or other piece of hardware, your system will ask you to install more software called a driver. What does a driver do? A driver is a specially written program, which understands the operation of the device it interfaces to, such as a printer, video card, sound card or CD ROM drive. It translates commands from the operating system or user into commands understood by the component computer part it interfaces with. It also translates responses from the component computer part back to responses that can be understood by the operating system, application program, or user. The below diagram gives a graphical depiction of the interfaces between the operating system and the computer component. Other Operating System Functions Page 7 of 24 Computer Literacy – Communications Information OTS 251/D Name Creator Predecessor Cost / Availability Preferred License Target system type 8. IRIX SGI Unix Bundled with hardware Proprietary Server, Workstation 9. Inferno Bell Labs Plan 9 Free MIT/GNU GPL/GNU LGPL/LPL NetApp, Server, Embedded 10. Linux Linus Torvalds, et al. Unix4, Minix5 See Comparison of Linux distributions GNU GPL, GNU LGPL and other licenses See: Comparison of Linux distributions 11. Mac OS Apple Inc. None2 7 Bundled with 68K and PowerPC Macs; versions 7-9 sold as retail upgrades3; Proprietary Workstation, Home Desktop 12. Mac OS X Apple Inc. NeXTStep / OPENSTEP / Rhapsody, Mac OS, UNIX Bundled with hardware; upgrades sold separately: Desktop $169 (Single User Mac Box Set), $29 (Single User Mac OS X v10.5 Upgrade) 13. Family Pack $229 (5 User Mac Box Set), $49 (5 uUser Mac OS X v10.5 Upgrade) Open source core system (Both Intel and PowerPC versions) (APSL, GNU GPL, others) with proprietary higher level API layers 14. Mac OS X Server Apple Inc. NeXTStep / OPENSTEP / Rhapsody, Mac OS Bundled with hardware; also sold separately: $499 (10 clients); $999 (unlimited clients) Open source core system (Both Intel and PowerPC versions) (APSL, GNU GPL, others) with proprietary higher level API layers 15. Minix3 Andrew S. Tanenbaum Minix2 Free BSD Workstation 16. NetBSD The NetBSD Project 386BSD Free BSD NetApp, Server, Workstation, Embedded 17. NeXTStep NeXT Unix Bundled with hardware, then sold separately Proprietary Workstation 18. NetWare Novell S-Net $184 (single-user) Proprietary Server 19. OpenBSD The OpenBSD Project NetBSD 1.0 Free BSD Server, NetApp, Workstation, Embedded 20. OpenVMS DEC (now HP) RSX-11M Free for non-commercial use Proprietary Server, Workstation 21. OS/2 IBM and Microsoft UNIX, Windows 3.x $300 Proprietary Home Desktop, Server 22. PC-BSD PC-BSD Software FreeBSD6 Free BSD Desktop, Workstation, Server 23. Plan 9 Bell Labs Unix Free LPL Workstation, Server, Embedded, HPC 24. QNX QNX Software Systems Unix ? Proprietary Workstation, Server, Embedded 25. Solaris Sun SunOS Free CDDL Server, Workstation 26. OpenSolaris Sun Solaris Free CDDL Desktop, Workstation, Server 27. Windows Server (NT family) Microsoft MS-DOS, OS/2, Windows 3.x $469 Web Server; other editions dependent on number of CALs purchased Proprietary Server, NetApp, Embedded, HPC 28. Microsoft Windows (NT family) Microsoft MS-DOS, OS/2, Windows 3.x Home Basic (Retail) $99.95, Home Premium (Retail) $119.95, Business (Retail) $299.95, Ultimate (Retail) $300.95[1] Proprietary Workstation, Home Desktop, media center, Tablet PC, embedded Page 10 of 24 Computer Literacy – Communications Information OTS 251/D Name Creator Predecessor Cost / Availability Preferred License Target system type 29. RISC OS Acorn Computers, RISC OS Limited, Castle Technology Ltd ARTHUR, also the BBC Master OS Bundled with hardware, then sold separately at $127 (£70) Proprietary educational desktop, home computer 30. ZETA yellowTAB BeOS R5 Professional $110, Student $80 Proprietary Home Desktop, Media Workstation 31. STOP 6 / XTS-400 BAE Systems STOP 5 / XTS-300 Unknown; supplied to customers on-demand by BAE Systems Proprietary Server, Workstation, cross- domain solution, network guard 32. ReactOS ReactOS development team Windows NT Free GNU GPL, GNU LGPL Workstation, Home Desktop 33. z/OS IBM OS/390 Monthly License Charge (about $130 and up) Proprietary IBM mainframe 8. Command Driven6 Refers to programs and operating systems that accept commands in the form of special words or letters. In contrast, programs that allow you to choose from a list of options in a menu are said to be menu driven. Command-driven software is often more flexible than menu-driven software, but it is more difficult to learn. 9. Graphical Operating System7 GEOS (Graphic Environment Operating System) was an operating system from Berkeley Softworks (later GeoWorks). Originally designed for the Commodore 64 and released in 1986, it provided a graphical user interface for this popular 8-bit computer. GEOS is currently owned and distributed by Breadbox Computer Company, LLC at http://www.breadbox.com GEOS closely resembled early versions of Mac OS and included a graphical word processor (geoWrite) and paint program (geoPaint). For many years, Commodore bundled GEOS with its redesigned and cost reduced C64, the C64C. At its peak, GEOS was the third most popular operating system in the world in terms of units shipped, trailing only MS-DOS and Mac OS. Other GEOS-compatible software packages were available from Berkeley Softworks or from third parties, including a reasonably sophisticated desktop publishing application called geoPublish and a spreadsheet called geoCalc. While geoPublish was not as sophisticated as Aldus Pagemaker and geoCalc not as sophisticated as Microsoft Excel, the packages provided reasonable functionality, and Berkeley Softworks founder Brian Dougherty claimed the company ran its business using its own software on Commodore 8-bit computers for several years. Enhanced versions of GEOS later became available for the Commodore 128 and the Apple II family. A lesser-known version was also briefly released for the Commodore Plus/4. Written by a group of programmers, led by Dougherty, who cut their teeth on limited-resource video game machines such as the Atari 2600, GEOS was revered for what it could accomplish on machines with 64–128 kB of RAM memory and 1–2 MHz of 8-bit processing power. 6 http://www.webopedia.com/TERM/C/command_driven.html 7 http://en.wikipedia.org/wiki/GEOS_(8-bit_operating_system) Page 11 of 24 Computer Literacy – Communications Information OTS 251/D Unlike many pieces of proprietary software for the C64 and C128, GEOS took full advantage of many of the add-ons and improvements available for these systems. Commodore's 1351 mouse was supported by GEOS, as were its various RAM expansion units. GEOS 128 also fully supported the C128's 640×200 high-resolution VDC display mode through a compatible RGB monitor. The C64 version of GEOS incorporated a built-in fast loader, called diskTurbo, that significantly increased the speed of drive access on the slow 1541. (GEOS 128 could take advantage of the C128's enhanced "burst mode" in conjunction with the 1571 and 1581 drives.) Via Berkeley's special geoCable interface converter or other third-party interfaces to connect standard RS-232 or Centronics printers to the Commodore serial bus, GEOS supported a wide variety of printers, including HP PCL printers and the Apple LaserWriter. This ability to print to high-end printers was a major factor in making GEOS a desktop publishing platform. The Apple II version of GEOS was released as freeware in August 2003. The Commodore 64/128 versions followed in February 2004. The Apple II version is freely available for download from Breadbox at http://www.breadbox.com The latest GEOS desktop suite is Breadbox Ensemble. Revivals were seen in the HP OmniGo handhelds, Brother GeoBook line of laptop-appliances, and the New Deal Office package for PCs. Related code found its way to earlier 'Zoomer' PDAs, creating an unclear lineage to Palm, Inc.'s later work. Nokia used GEOS as a base operating system for their Nokia Communicator series, before switching to EPOC (Symbian). 10. Trends in Operating System Development Faster Computers Permit New Applications The rapid increase in computer power creates new software opportunities, such as photo and video editing. Most developers of user applications create successive versions of the same product, taking advantage of greater computer speed to improve products by making them faster or capable of handling new functions. Foreign Staff Outsourcing Because the high cost of US programmers, some software companies are outsourcing part of their production work to other countries, especially India. Developments in communication technology and software that allows multiple users to collaborate have made foreign outsourcing easy. Linux Linux is an operating system with "open source code"; that is, all parts are open to users to examine and modify if they desire. (The source code for Windows operating systems is a closely-guarded secret.) Linux is a low-cost and powerful alternative to proprietary versions of UNIX that are used to operate computer servers, and has become more popular in recent years. Video Games One software sector with high growth in recent years is video game development. The US retail market for video games is now larger than the movie industry. Companies develop video games for PCs and various "consoles" -- specialty computers like PlayStation, Xbox, and GameCube, made by Sony, Microsoft, and Nintendo, respectively. US retail sales of video games were over Page 12 of 24 Computer Literacy – Communications Information OTS 251/D Security concerns exist for simple RITA/telnet as the communications is un-encrypted and could theoretically be eavesdropped on by unscrupulous individuals. Good hardware-based firewalls should be employed to protect your servers, allowing only RITA/telnet services through. This can be a restriction if the technology architecture requires use of other network services. Furthermore, login/pass-wording must be well managed on the servers so that only authorized users can gain access. Virtual Private Network (VPN) For those requiring better security, VPN offers encrypted communications between devices. Both ends of a VPN connection must use a common encryption key, also known as a "private key." Then, the devices use that private key to encrypt all packets exchanged between them. This technology is believed to be secure and reliable. VPN Tunneling--Wide Area Network VPNs provide their services through the ability to "tunnel" through the Internet. Not only are the communications encrypted, the two networks are connected in a virtual "Wide Area Network" (WAN) configuration. This allows secure exchange of all types of networked-based services from file and print sharing to Network File Systems (NFS). A correctly configured WAN can provide all services typically associated with a Local Area Network (LAN), and can save money in line costs and reduce overall expenses. Other Networking Services Internet access also has a whole range of additional services, many of which add great value to distributors information management technology. Some of these services are; Web Browsing--Web Browsing enables PC users to visit manufacturers' websites for product information and the ability to place orders. Liquid Computing Showcases Converged Communications and Computing Platform at... High performance computing and communications; proceedings Networks security, wireless communications and trusted computing;... E-mail--This correspondence can replace phone calls to branches and the long distance toll charges they incur. The ability to send email to multiple parties at the same time reduces duplicate efforts and increases awareness amongst all recipients. Instant Messaging--This newest form of instant, non-verbal communications rivals the telephone in its ability to interrupt and demand instant answers from "buddies" logged in anywhere on the Internet. Care should be exercised when implementing this technology as abuse is easy and sometimes difficult to police. Users can appear to be working on company business while actually chatting on-line. Voice-Over-Internet-Protocol (VOID)--VOIP phones connect the handsets in the branch to the Page 15 of 24 Computer Literacy – Communications Information OTS 251/D main phone system in the central office. Phone conversations are digitized and packaged for transmission through the Internet. No more long distance toll charges to call the branch office. Better yet, with some phone systems, the remote handset can operate as a full function telephone capable of accessing voice mail and transferring calls. With a VOIP network, a company can save money on inter-branch long distance toll charges. Types of Connections--One of the tremendous advantages of IP communications is their ability to utilize a variety of Internet connections. T-1 circuits provide the highest band-width available (1500K baud), and at the highest price point too ($900-$1,500 per month). DSL (Digital Subscriber Line) and cable modems offer similar broadband speeds at considerable price savings ($80-$200 per month) over T-1 lines. These circuits generally offer 128K baud- 768K baud upload speeds with faster download speeds. Even simple 56K baud dial-up circuits offered by local Internet Service Providers can be used for $15-$25 per month plus the cost of the phone line. However, 56K baud dial-up lines should he considered only as a last resort for small branches. Furthermore, static IP addresses are rarely available with dial-up circuits and therefore don't suffice for the main office connection. Full-time access is needed at the main office with the ability to connect at any hour of the day or night, and the server needs to he on-line to take the call. That Internet connection will require a publicly accessible "static IP address." Within the Internet, an IP address is akin to your telephone number. Many dial-up Internet connections are given a new ("Dynamic") IP address each tune the connection is established. Just like in the telephone world, it is difficult to receive incoming phone calls if your phone number changed every time it was used. That is true for the Internet world; it is difficult to connect to your server if it's IP address is subject to change. Hence, a "static IP address" doesn't change over time. Pitfalls DSL and cable companies are struggling to ramp up to the demand for new, low-cost broadband offerings, and often promise services or installation schedules not met. Research broadband availability and arrange its installation prior to disconnecting existing legacy equipment. Long-term contracts for broadband service should be avoided if possible as costs continue to drop dramatically by vendors competing for market share. Today's "bargain" will certainly be overpriced in time. New, IP-based PC hardware is generally more expensive to buy and maintain than its "dumb" terminal counterpart. Organizations must consider the deployment and maintenance costs for the new, more sophisticated platform. Case Study A medium-sized, independent welding supply/industrial gas distributor with three branches within 150 miles of the main office, all a long-distance toll call to each other, had traditional four- wire, 9,600 baud, analog leased lines to connect dumb terminals and printers in the branches to the mainframe system. Performance of the devices were acceptable, but newer technologies for Internet access were non-existent. Communication costs for the lines was about $1,300 per month. Page 16 of 24 Computer Literacy – Communications Information OTS 251/D A severe storm at one of the branches destroyed most of the serial communications hardware and dumb terminals/printers, so alternatives were investigated. Fifty-six K baud digital point-to- point circuits were initially promoted by the incumbent telco, but had no significant cost savings or enhanced functionality. The Frame Relay circuits did reduce the overall monthly cost slightly, but required the a transition to IP-based terminal devices, thereby making the investment payback long RITA plus VPN was investigated to connecting the branches though the Internet. A typical DSL connection was about $79 per month per location with an $20 per month fee for the required static IP address at the main office. One branch was not served by DSL or cable, therefore 56K baud dial-up was implemented about $50 per month. Total monthly communication costs are now $300, yielding a savings of $1,000 per month. This savings can be applied to the cost of the new IP-based PCs, communications hardware, and print servers needed at the branches with a projected payback period of less than two years. The additional benefits include: Internet access, email, instant messaging between the branches, and reduced long distance toll charges. David J. Frea is president of Infonetics, Inc. He can be reached by phone at 614.875.2006, or email at djf@infonetx.com. 12. Using Computers as Communication tools10 The following are excerpts from a web-posted paper providing insights on how one entity used the computer as a communication tool to reach a target population. Communication is a skill, which is used to provide and receive information. How one receives and provides this information is one issue, the other is what information is being provided or received. At a basic human level, communication can exist through verbal or non-verbal cues, such as what is said, how we say it, and the position of our bodies. What makes communication effective is the ability of the provider to have the skills and tools available to send information, and the receiver to also have to the skills and tools to obtain the information. Throughout the history of humankind communication has evolved from using basic sounds and visual images such as drumming or cave drawings, to more advanced sounds such as music, language and sirens, and visually through written language. The tools, which make communication effective, have also evolved. The inventions of the telephone, and printing press changed dramatically how people could communicate with each other, as distance was no longer an obstacle, and through books and newspapers, numerous peoples could be reached. Television, film and radio has also created a medium by which communication could be provided. The media of television, newspapers, radio have also been stifled as an completely effective tool of communication, as these have always been owned by a source, usually capitalist, therefore the actual information is either edited or censored in order to meet the needs of the owners, be it state or private. Since the digital revolution of the 1970's, new technology has changed the way in which information can be provided/received. How this technology works is not necessarily required in 10 THE TRADE UNION MOVEMENT AND THE INTERNET, by Marie Dancsok, Final Project, Year II, European Labour Studies, South Bank University, For: Richard Ross, June 26, 1996; http://www.labournet.org.uk/sbu/internet.html Page 17 of 24 Computer Literacy – Communications Information OTS 251/D 14. Computer Networks12 A computer network is a group of interconnected computers. Networks may be classified according to a wide variety of characteristics. This article provides a general overview of some types and categories and also presents the basic components of a network. Connection method Computer networks can also be classified according to the hardware and software technology that is used to interconnect the individual devices in the network, such as Optical fiber, Ethernet, Wireless LAN, HomePNA, Power line communication or G.hn. Ethernet uses physical wiring to connect devices. Frequently deployed devices include hubs, switches, bridges and/or routers. Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves or infrared signals as a transmission medium. ITU-T G.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high-speed (up to 1 Gigabit/s) local area network. Wired Technologies Twisted-Pair Wire - This is the most widely used medium for telecommunication. Twisted-pair wires are ordinary telephone wires which consist of two insulated copper wires twisted into pairs and are used for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed range from 2 million bits per second to 100 million bits per second. Coaxial Cable – These cables are widely used for cable television systems, office buildings, and other worksites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed range from 200 million to more than 500 million bits per second. Fiber Optics – These cables consist of one or more thin filaments of glass fiber wrapped in a protective layer. It transmits light, which can travel over long distance and higher bandwidths. Fiber-optic cables are not affected by electromagnetic radiation. Transmission speed could go up to as high as trillions of bits per second. The speed of fiber optics is hundreds of times faster than coaxial cables and thousands of times faster than twisted-pair wire. Terrestrial Microwave – Terrestrial microwaves use Earth-based transmitter and receiver. The equipment look similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all communications to line-of-sight. Path between relay stations spaced approx. 30 miles apart. Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks. Communications Satellites – The satellites use microwave radio as their telecommunications medium, which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically 22,000 miles above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals. 12 http://en.wikipedia.org/wiki/Computer_network Page 20 of 24 Computer Literacy – Communications Information OTS 251/D Cellular and PCS Systems – Use several radio communications technologies. The systems are divided to different geographic area. Each area has low-power transmitter or radio relay antenna device to relay calls from one area to the next area. Wireless LANs – Wireless local area network use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANS use spread spectrum technology to enable communication between multiple devices in a limited area. Example of open-standard wireless radio-wave technology is IEEE 802.11b. Bluetooth – A short-range wireless technology. Operate at approx. 1Mbps with range from 10 to 100 meters. Bluetooth is an open wireless protocol for data exchange over short distances. The Wireless Web – The wireless web refers to the use of the World Wide Web through equipments like cellular phones, pagers,PDAs, and other portable communications devices. The wireless web service offers anytime/anywhere connection. Types of networks Below is a list of the most common types of computer networks in order of scale. Personal area network A personal area network (PAN) is a computer network used for communication among computer devices close to one person. Some examples of devices that are used in a PAN are printers, fax machines, telephones, PDAs, and scanners. The reach of a PAN is typically about 20-30 feet (approximately 6-9 meters), but this is expected to increase with technology improvements. Local area network A local Area Network (LAN) is a computer network covering a small physical area, like a home, office, or small group of buildings, such as a school, or an airport. Current wired LANs are most likely to be based on Ethernet technology, although new standards like ITU-T G.hn also provide a way to create a wired LAN using existing home wires (coaxial cables, phone lines and power lines)[2]. For example, a library may have a wired or wireless LAN for users to interconnect local devices (e.g., printers and servers) and to connect to the internet. On a wired LAN, PCs in the library are typically connected by category 5 (Cat5) cable, running the IEEE 802.3 protocol through a system of interconnected devices and eventually connect to the Internet. The cables to the servers are typically on Cat 5e enhanced cable, which will support IEEE 802.3 at 1 Gbit/s. A wireless LAN may exist using a different IEEE protocol, 802.11b, 802.11g or possibly 802.11n. The staff computers (bright green in the figure) can get to the color printer, checkout records, and the academic network and the Internet. All user computers can get to the Internet and the card catalog. Each workgroup can get to its local printer. Note that the printers are not accessible from outside their workgroup. Typical library network, in a branching tree topology and controlled access to resources All interconnected devices must understand the network layer (layer 3), because they are handling multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection to the central Page 21 of 24 Computer Literacy – Communications Information OTS 251/D router, could be called "layer 3 switches" because they only have Ethernet interfaces and must understand IP. It would be more correct to call them access routers, where the router at the top is a distribution router that connects to the Internet and academic networks' customer access routers. The defining characteristics of LANs, in contrast to WANs (Wide Area Networks), include their higher data transfer rates, smaller geographic range, and lack of a need for leased telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s. This is the data transfer rate. IEEE has projects investigating the standardization of 40 and 100 Gbit/s.[3] Campus area network A campus area network (CAN) is a computer network made up of an interconnection of local area networks (LANs) within a limited geographical area. It can be considered one form of a metropolitan area network, specific to an academic setting. In the case of a university campus-based campus area network, the network is likely to link a variety of campus buildings including; academic departments, the university library and student residence halls. A campus area network is larger than a local area network but smaller than a wide area network (WAN) (in some cases). The main aim of a campus area network is to facilitate students accessing internet and university resources. This is a network that connects two or more LANs but that is limited to a specific and contiguous geographical area such as a college campus, industrial complex, office building, or a military base. A CAN may be considered a type of MAN (metropolitan area network), but is generally limited to a smaller area than a typical MAN. This term is most often used to discuss the implementation of networks for a contiguous area. This should not be confused with a Controller Area Network. A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings. Metropolitan area network A metropolitan area network (MAN) is a network that connects two or more local area networks or campus area networks together but does not extend beyond the boundaries of the immediate town/city. Routers, switches and hubs are connected to create a metropolitan area network. Wide area network A wide area network (WAN) is a computer network that covers a broad area (i.e. any network whose communications links cross metropolitan, regional, or national boundaries [1]). Less formally, a WAN is a network that uses routers and public communications links Contrast with personal area networks (PANs), local area networks (LANs), campus area networks (CANs), or metropolitan area networks (MANs), which are usually limited to a room, building, campus or specific metropolitan area (e.g., a city) respectively. The largest and most well-known example of a WAN is the Internet. A WAN is a data communications network that covers a relatively broad geographic area (i.e. one city to another and one country to another country) and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer. Global area network Page 22 of 24