Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Web 101 Third Edition Created by Wendy G. Lehnert & Richard L. Kopec Modified by Linda Kenney January 22, 2008 Chapter 1: First Things First

1-2 Understand the purpose of your computer’s CPU, RAM, and secondary storage. Learn about bits, bytes, kilobytes, megabytes, and gigabytes. Find out how the Internet is structured and how computers become part of the Internet. Discover how IP and DNS addresses are used. Master the basic navigational features of your Web browser. Learning Objectives

1-3 The Internet (or Net) is used by students and others for many purposes. What are some purposes? Taking Charge

1-4 Organization of a Computer System Central Processing Unit Main Memory Input Device Output Device Secondary Storage

1-5 The CPU (Central Processing Unit) Fetches instructions from main memory Carries out the operations commanded by the instructions Each instruction produces some outcome

1-6 Random Access Memory (RAM) –This is also called Main Memory Long-term storage Memory and Storage

1-7 Random Access Memory (RAM) The memory that the CPU uses when it executes instructions The CPU reads and writes to RAM very quickly RAM is volatile - the information goes away when the computer is turned off or restarted (short-term) Each program that you run requires some amount of RAM Main Memory (or Primary Storage)

1-8 Secondary Storage A nonvolatile (or “permanent”) storage medium Contents retained while power is off Hard disk drives are most common –Records data magnetically on a circular disk –Provides fast access to large amounts of data Optical devices store data on CD’s as pits USB flash memory devices –High capacity device plugs into USB port –Portable, reliable, and fits easily in a pocket

1-9 Software The programs that run on a computer Two major categories –Operating systems Controls the processes within the computer Manages the computer's hardware devices –Application Software Solve problems or perform tasks needed by users Examples include word processing, spreadsheets, games, Internet browsers, playing music, etc) Each program is referred to as an application

1-10 The size of files is measurable. The smallest unit of data is the bit. –A bit is either a 1 or a 0 –All data (and files) are a pattern of bits A byte is 8 bits –Each byte can represent a character (letter, number or symbol). –The set of upper and lowercase letters, numbers, and other symbols is called the ASCII character set. Units of Memory

1-11 For more info, see

1-12 Kilobyte (K): 1024 bytes Megabyte (MB): 1024 kilobytes Gigabyte (GB): 1024 megabytes Terabyte (TB): 1024 gigabytes Units of Memory

1-13 Types of Files Besides the size, there are two types of files: –ASCII text files contain ASCII characters –Binary files contain characters that cannot be typed on the keyboard, generated by software

1-14 Units of Memory (see p. 16)

1-15 The Internet is a network of networks that are spread all over the world. Networks that are geographically close are called Local Area Networks (LANs). –Often in the same building –The university’s network is a prime example The Internet is a largely heterarchical network containing many individual LANs. The Internet

1-16 Some Network Basics A computer network is two or more computers connected together so that they can communicate.

1-17 Some Network Basics (cont.) –Computers connected to a network are commonly called hosts. –The connection that carries data among hosts is called the transmission medium.

1-18 Network basics (cont.) All the hosts on the network must somehow share the transmission medium. Only one data transfer can take place at a time on the transmission medium. (Draw the diagram.) –This means that if host A is transferring data to host B, and host C needs to transfer data to host D, host C must wait until host A is done before it begins its transfer. –If host A is transferring a lot of data to host B, host C could end up waiting a long time. –For this reason, it’s not desirable to give host A exclusive access to the transmission medium until it’s done with its transfer. –Instead networks use a system to ensure that access to the transmission medium is shared equally among all connected hosts. This system is called packet switching.

1-19 Packet switching (see p , also) Packet switching avoids network delays by ensuring that access to the transmission medium is shared equally by all hosts. –Each host that has data to transfer is given a turn. –During its turn, each host gets exclusive access to the transmission medium.

1-20 Packet switching (cont.) –However, the total amount of data it’s allowed to transfer during its turn is strictly limited. The largest amount of data a single host is allowed to transfer during one turn determines the size of a single packet. Data that is bigger than the packet size for the network must be broken up into multiple packets. If a host needs to send multiple packets, it must wait for later turns to send the others. No host is allowed to send more than one packet per turn.

1-21 Packet switching (cont.) –Every packet is labeled with the identity of the host that sent it and the identity of the host for which it’s destined. Every host on a given network must therefore have a unique identity. –Host identities are called addresses. –Every network must have rules to determine how these identities are assigned. And every packet must be constructed and labeled according to a common set of rules as well. When we need common rules for computers to follow, we define protocols.

1-22 Packet Example As an example, let's look at how an message might get broken into packets. Let's say that you send an to a friend. The is about 3,500 bits (3.5 kilobits) in size. The network you send it over uses fixed-length packets of 1,024 bits (1 kilobit). The header of each packet is 96 bits long and the trailer is 32 bits long, leaving 896 bits for the payload (actual message). To break the 3,500 bits of message into packets, you will need four packets (divide 3,500 by 896). Three packets will contain 896 bits of payload and the fourth will have 812 bits. Here is what one of the four packets would contain: From

1-23 Packet Example (cont.) From

1-24 A heterarchical network contains many nodes that are interconnected. A hierarchical network contains a tree-like structure where some nodes are superior to others. Heterarchical vs. hierarchical

1-25 Heterarchical vs. hierarchical (cont.)

1-26 A characteristic of a heterarchical network is that it is a robust network. If some nodes are removed, data can still be sent between nodes Hierarchical networks do not lend themselves to robustness The Internet also has dynamic routing, where the route of the data is determined at the time of transmission based on current network conditions. Heterarchical vs. hierarchical (cont.)

1-27 Each computer on the Internet is a host machine. Each computer has a unique Internet Protocol (IP) address, such as –Some computers have a permanent IP address –Some computers borrow an IP address while they are connected to the Internet An IP address is not human-friendly Host Machines and Host Names

1-28 IP addresses Because there are so many computers on the Internet, IP addresses must be very large numbers. –Since it’s hard to work with very large numbers accurately, IP addresses are commonly written using dotted quad notation. Dotted quad notation consists of four numbers (in the range 0 to 255) separated by dots (or periods) For example, is the IP address for the cisunix computer named turing

1-29 Assignment of IP addresses Every single computer added to the Internet must be given an IP address that is not already in use. With millions of computers already on the Internet and thousands more being added every day, that’s a considerable challenge. It’s not practical for each individual computer user to come up with their own unique IP address.

1-30 Assignment of IP addresses (cont.) Since virtually all connections to the Internet are managed by an organization of some sort (school, company, ISP, etc.), it’s much more practical to place each organization in charge of its own addresses. –When an organization first establishes a connection to the Internet, it is assigned an address space consisting of the first one, two or three values in a dotted quad address.

1-31 Assignment of IP addresses (cont.) –Once assigned such an address space, the organization is free to assign the remaining three, two or single values as it sees fit to each computer it connects to the Internet. –No other organization is entitled to create addresses within that assigned address space. –And the organization that owns a given address space is solely responsible for ensuring that no address within that space is ever in use by two computers at the same time. –At UNH, our address space consists of all addresses that begin with

1-32 Assignment of IP addresses (cont.) Remember: –IP addresses are assigned in a delegated manner. –Users are assigned IP addresses by organizations (UNH, Internet service providers (ISPs), etc. ISPs obtain allocations of IP addresses from a local Internet registry (LIR) or national Internet registry (NIR), or from their appropriate Regional Internet Registry (RIR):

1-33 The IP address for most host machines are mapped to a Domain Name Service (DNS) address in order to be more people-friendly. The DNS address consists of a host name followed by a domain name Example DNS Address: mail.yahoo.com –Host Name is: mail –Domain Name is: yahoo.com Host Machines and Host Names

1-34 Each domain name consists of: –Institutional site name –Top Level Domain name (TLD) Host Machines and Host Names

1-35 Examples of TLDs include: –.coma commercial organization –.edua US educational site –.neta network site –.auAustralia –.frFrance –.hkHong Kong –.esSpain New TLDs have been added as the original set became overloaded. Examples? Host Machines and Host Names

1-36 Example: cs.unh.edu –Host name? –Domain Name? –Top Level Domain?

1-37 Anyone can register a DNS address When you type in a DNS address, a domain name server translates it into an IP address. Domain Names

1-38 Assignment of hostnames Since hostnames, like IP addresses, establish identities for hosts, they too must be unique across the entire Internet. –Recall that with IP addresses, an organization is assigned a unique address space when it connects to the Internet. –At the same time, an organization also typically obtains a unique domain name.

1-39 Network Information Center (NIC) The InterNIC Website! This website has been established to provide the public information regarding Internet domain name registration services.

1-40 When you go online, your computer exchanges data with other computers. The transfer of data is measured in bits per second (bps); bandwidth Your data transfer rate is determined by: –The type of connection (e.g. dial-up) (see p. 68) –The traffic over the network The bottleneck is the part of your connection that slows the data rate during transfer Speed and Bottlenecks

1-41 Clients and servers are host machines. A client is the host machine that requests information from the server. The server is a resource that provides a service for (many) clients. The client/server interaction is the foundation for all Internet communication. The Client/Server Software Model

1-42 The Client/Server Software Model

1-43 Internet services What the Internet allows us to do is determined by the services that it provides. –When we are using the Internet, we are utilizing one or more of these Internet services. World Wide Web allows self-publication in electronic formats. allows directed communication with other Internet users. Remote login allows computers to be controlled remotely by users on other computers. File transfer allows files to be moved and copied between various computers.

1-44 The Web and the Internet are not the same. The World Wide Web has become a popular means of accessing information and services. A Web browser is the software necessary to view information. The World Wide Web and Web Browsers

1-45 Navigating the Web only takes a few commands. The information in the Web is organized as hypertext, graphics, video, and sound. The text in a Web page may contain hyperlinks that, if clicked, allows you to view related information on other Web pages. You control where you go and what information you see via these hyperlinks. The World Wide Web and Web Browsers

1-46 A Web page is a document on the Web that you view through your Web browser. The act of reading Web pages and clicking on hyperlinks is called browsing (basically, exploring). Each Web page has a unique address called a Uniform Resource Locator (URL) that you can use to jump directly to it. The World Wide Web and Web Browsers

1-47 URL Uniform Resource Locator URL Represents the address of a resource on the Internet.

1-48 Before you can use Internet resources, you need to get access to the Internet. Many students use their accounts on university computers. Others use the computers at the library, their workplace, or even that of a friend. Others will need to get an account and software through a commercial Internet Service Provider (ISP). Examples? How to Get Online

1-49 An ISP provides technical support for the provided software. Your account gives you a userid and password. How to Get Online (cont.)

1-50 Select your own default home page –When you start your browser, a default Web page is displayed. –You can change the default page to another URL. Use the Find command –Find allows you to find text in a page. –You enter the text that you want to find. –If that text is in the page, then you view the first instance of the text in the page. Browser Tips and Tricks

1-51 Use your History list –The History list is a list of the URLs that you have visited recently. –You can click on a URL from the list to revisit the page. Abort a download if you get stuck –If the browser appears to be stuck while loading a page, select the option to stop the page loading. –The page may display, but if not try clicking on the link again. Browser Tips and Tricks (cont.)

1-52 Browser Tips and Tricks (cont.) Use Bookmarks (Favorites) –A bookmark is a pointer to a Web page that you expect to revisit. –You can select a bookmark from a list, and quickly jump to that Web page. Add Bookmarks with care –Bookmarking every page of interest is tempting. –Large bookmark lists are difficult to use. –Create folders for your bookmarks.

1-53 Turn off graphics –Graphics files can be large and take a long time to download. –If you are in a hurry or have a slow Internet connection, then you may spend time waiting for pages to load. –You can set your browser to not download graphics. Browser Tips and Tricks (cont.)

1-54 Use the Phishing Filter –Phishing is a form of Social Engineering (see Chapter 2) designed to get unwary users to enter sensitive information (like passwords or account numbers) for nefarious purposes. –Your browser warns you when visiting a known phishing site. –But - your browsing history must be monitored to enable this feature. Browser Tips and Tricks (cont.)

1-55 Dear Amazon Member, We recently noticed an attempt to log in to your Amazon account from a foreign Ip address and we have reason to believe that your account was used by third party without your authorization. If you recently accessed your account while traveling,the unusual log in attempts may have been initiated by you.Therefore,if you are the rightful account holder, click on the link below to log into your account and follow the instructions. if you choose to ignore our request,you leave us on choice but to temporarily suspend your account. If you received this notice and you are not authorizes account holder,please be aware that it is in violation of Amazon policy to represent oneself as another Amazon user.Such action may also be in violation of local,rational,and/or international law. Amazon is committed to assist law enforcement with any inquires related to attempts to misappropriate personal information with the intent to commit fraud or theft. Information will be provided at the request of law enforcement agencies to ensure that impersonators are prosecuted to the fullest extent of the law Thank you for your patience as we work together to protect your account Sincerely, Amazon Account Review Department

1-56 Don’t let a “404 Not Found” message stop you. –The error means that the specified URL was not found. –Check that the URL was correct. –The page may have been removed or moved. –You can always backtrack through the URL to see if a related part of the site is available. –HOW? Browser Tips and Tricks (cont.)

1-57 Avoid peak hours –The Internet has times of high traffic where response times are slower than off-peak times –In the US, the peak times of usage during the week are: The middle of the day Early evenings Browser Tips and Tricks (cont.)

1-58 Other Useful browser Features found on page 49 –Automatic Update –Bookmark Import/Export –Bookmark manager –Content Advisor –Cookie Manager –Customization –Download Manager –Form Manager Browser Tips and Tricks (cont.)

1-59 Other Useful browser Features (cont.) –History Manager –Integrated Search –Javascript Disable –Password Manager –Pop-up Blocker –RSS Feeds –Security Manager Browser Tips and Tricks (cont.)

1-60 Firefox –Available for Windows and Mac –Replaces the aging Mozilla browser – Mozilla (aka SeaMonkey) –Available for Windows and Mac –Includes web page editor, mail client, Usenet News reader, IRC Chat cient – – Alternate Web Browsers (pp. 51 – 58)

1-61 Netscape –Available for Windows and Mac –Based on Firefox browser –Includes integrated Security Center – Opera –Available for Windows and Mac –Includes widgets and a BitTorrent client (see Section 6.4.1) – Alternate Web Browsers

1-62 Safari –Includes “Private Browsing” feature which keeps no record of sites visited – Camino, iCab, Shiira – (Camino) – (iCab) – (Shiira) Mac Only Web Browsers