【计算机系统导论】7.1 概述


Networking has transformed computers from stand-alone data-crunchers into the foundation of an unprecedented global community. Networking rests on a simple concept: getting computers to communicate with each other.

This requires a physical connection, like wires or radio links, and a common language (protocol) for exchanging data. Once these are in place comes the layer we see: information systems like the Web.

What’s the Difference Between the Internet and the Web?

The Internet, linking your computer to other computers around the world, is a way of transporting content. The Web is software that lets you use that content…or contribute your own. The Web, running on the mostly invisible Internet, is what you see and click on in your computer’s browser.

The Internet’s roots are in the U.S. during the late 1960s. The Web was invented 20 years later by an Englishman working in Switzerland—though it had many predecessors.

To keep things “interesting,” many people use the term Internet to refer to both.

The Victorian “Internet”

Your great-great-Grandma wasn’t surfing the Web. But she may have been sending digital messages.

From ancient Greece until the 19th century, the semaphore was the fastest way to send messages. People used flags or lights to signal between line-of-sight stations. But in the 1830s, the telegraph pioneered a new concept: carrying information with electricity. That “big idea” became a building block of computers and telecommunications.

Telegraph networks rapidly circled the globe, joined later by telephones. Their providers evolved into some of the first major technology companies—many of which remain dominant players in telecommunications.

Going Digital: Morse Code

Morse code, the most common “language” of telegraph systems, represents information digitally.

Electrical switches made “dots” and “dashes”—like a computer’s ones and zeros. Receivers turned these pulses into sounds. Messages were sometimes stored on paper tape as embossed lines or, later, punched holes that could be read by machine.

Morse code chart

Redesigned by Samuel Morse’s assistant Alfred Vail around 1840, “Morse” code was more reliable than competing systems. It dominated telegraphy, and later, military and long distance radio communications, until the 1990s.

Connecting Over Phone Lines

Telecommunications was already a century old when digital computers appeared in the 1940s using similar technology: relays and vacuum tubes. Connecting computers to telegraphy devices such as teleprinters and paper-tape readers was natural.

Leasing telegraph lines was expensive, however. Could computers send data over switched telephone lines instead? Yes, with “modems”—devices that turned digital data into sound for transmission, then back into data.

Until the 1960s, computers mostly used phone and telegraph equipment to communicate. Only as they began connecting to other computers did systems optimized for computer communication develop.


With roots in 1840s printing telegraphs and 1860s tickertape machines, teleprinters had become mainstays of global messaging and text broadcast systems by the 1920s. Punched paper tape automated message transmission.

An elaborate teleprinter network supported global newswire services such as AP and Reuters. Later, teleprinters served as early computer terminals.

Computers Learn to “Talk”

Telephone networks carry sound: our voices. Using them for data required giving computers a voice.

The modem, developed at MIT’s Lincoln Labs in 1949, modulates computer data into sounds, and demodulates received sounds into digital data. (MODulation + DEModulation = MODEM.) Court decisions compelled telephone monopolies to open their lines to competitors’ modems.

Digital Phone Lines

Phone companies developed digital transmission to put many calls on each line connecting their switching centers. By 1958, this had produced the T1 standard still used in North America. Phone companies were leasing digital lines to commercial customers by the 1980s.

Many People, One System

Many People, One System

By the late 1950s, many people could share a single computer, using terminals to log in over phone lines. These timesharing computers were like central hubs with spokes radiating to individual users.

Although the computers generally couldn’t communicate with each other, these were the first common multi-user systems. Timesharing pioneered many features of later networks, from file sharing to e-mail and chat.

Typical 1960s users were a mix of business people, banks, students and researchers, military personnel, and customers of specialized services such as the SABRE airline reservation system.

SAGE Air Defense System: Network Pioneer

Designed to detect enemy airplanes in the 1950s, SAGE pioneered many technologies—including special-purpose networking. The computers communicated with radar stations, counter-attack aircraft, and each other — all in real-time, as potentially threatening events were happening.

SAGE (Semi Automatic Ground Environment)

This nuclear attack warning system pioneered special-purpose networking, with 23 connected centers across the continent.

Connections: Global Networks

J.C. Licklider

“Lick” was first head of the computer division of ARPA. He once wryly called his Web-like dream of person-computer symbiosis an “Intergalactic Computer Network.”

In the 1950s, users could connect remotely to a timesharing computer. Some networks, like those for SAGE, linked special-purpose machines together. But visionaries such as J.C.R. Licklider conceived networks able to globally unite different kinds of computers – a radical idea, and difficult to achieve.

There were daunting obstacles. How to translate between incompatible systems? How to harness a phone network designed for long conversations and use it for bursts of computer data? How to deal with noise and unreliable links? Each obstacle was overcome in time.

J.C. Licklider View Artifact Detail
J.C. Licklider

“Lick” was first head of the computer division of ARPA. He once wryly called his Web-like dream of person-computer symbiosis an “Intergalactic Computer Network.”

Connections: Global Networks

In the 1950s, users could connect remotely to a timesharing computer. Some networks, like those for SAGE, linked special-purpose machines together. But visionaries such as J.C.R. Licklider conceived networks able to globally unite different kinds of computers – a radical idea, and difficult to achieve.

There were daunting obstacles. How to translate between incompatible systems? How to harness a phone network designed for long conversations and use it for bursts of computer data? How to deal with noise and unreliable links? Each obstacle was overcome in time.

Packet Switching

“Packet switching” gave computers a reliable, efficient way to communicate over unreliable links.

In traditional telephone circuits, signals travel over one particular path. If it is blocked, nothing gets through. And when nothing is being said, the line is wasted.

In the early 1960s, several researchers, notably Paul Baran in the U.S. and several years later Donald Davies in the U.K., independently proposed a revolutionary alternative. Packet switching divides data into small chunks, called packets. Each travels separately and can take different routes. If one path is blocked, packets take an alternate route—or are resent.

ARPANET: Networking Takes Off

In the late 1960s, the U.S. Department of Defense’s Advanced Research Projects Agency (ARPA) adopted packet switching for its ARPANET computer network. Although Larry Roberts at MIT had run trials for ARPA, this was the first large-scale experiment in general-purpose computer networking. It evolved as part of a fertile collaboration among government, academia, and industry.

But soon ARPANET wasn’t alone. If it weren’t for ARPANET’s massive funding from the Defense Department, Britain’s NPL network, or France’s Cyclades network, might have overtaken it.

Inventing the Internet

Early networks successfully connected computers. But different kinds of networks couldn’t link to each other. So, the next challenge was creating “networks of networks,” a process called internetworking.

France’s CYCLADES and Britain’s NPL network were experimenting with internetworking in the early 1970s. Xerox PARC began linking Ethernets with other networks. These influenced ARPA’s TCP/IP internetworking protocol development led by Vint Cerf and Bob Kahn.

In 1977 Cerf and Kahn successfully linked three networks in a dramatic round-the-world transmission from a cruising van. In 1983, the entire ARPANET adopted the TCP/IP protocol. The Internet was born.

Internetworking as a Business

Connecting networks to each other requires special-purpose computers called gateways or routers as intermediaries. Some of the first gateways were repurposed ARPANET Interface message Processors (IMPs) from BBN. By the late 1970s, BBN was selling these and other dedicated gateways around the world.

An aggressive Silicon Valley startup called Cisco emerged from the Stanford University Artificial Intelligence lab, however, and soon dominated the router business.

Because most Cisco routers came ready to run Internet protocols, they helped spread the Internet globally—sometimes even to organizations officially supporting competing standards.

Protocol Wars

Everyone agreed on the goal: develop a global computer network. They didn’t agree on how. By the early 1980s, several different protocols competed.

OSI (Open Systems Interconnect), backed by European telephone monopolies and most governments, was favored. Other strong competitors included two corporate networks, IBM’s SNA and DEC’s DECNET. The dark horse contender was the Internet, defined only by a self-governing community dependent on volunteers.

The Internet community was nimble—able to develop in months what took the OSI committee-based process years—but it scared off some potential adopters because nobody seemed “in charge.”

We reject kings, presidents and voting. We believe in rough consensus and running code. by David Clark at a 1992 talk describing the Internet Engineering Task Force

Rough Consensus and Running Code

Big projects, like inventing a new network, are commonly run from the top down, by companies or standards-setting bodies. The young ARPANET community evolved its own bottom-up style of productive yet unstructured group collaboration.

Participants solved problems on their own, and then contributed their solutions to the group as RFCs (Request for Comments). The best RFCs became standards. The meritocratic, peer-reviewed approach was similar to the process for scientific research.

That freewheeling style became a model for later projects, including the Web and open source communities.

The Internet Comes From Behind

In 1980, the Internet was a medium-sized experiment with 213 computers. As late as 1988, insiders were betting against it. By 1992, it was emerging as the global winner, linking a million computers.

In hindsight, the Internet had key advantages, from a growing community of enthusiasts churning out working software and hardware, to free distribution with UNIX.

But the decisive factor? Probably money—especially U.S. government support from the National Science Foundation. Besides building infrastructure, NSFNET fueled the viral spread of networking in higher education.

Worms and Viruses: Dark Side of the Net

In a wired world, malicious users are connected too. That stark fact came clear in 1988 when the “Morris Worm” infected over 6000 computers in hours.

The possibility had been predicted in the 1960s and demonstrated in the 1970s. The name “worm” was inspired by John Brunner’s 1975 novel, Shockwave Rider.

Connections: Local Networks

Computers had to communicate down the hall, as well as globally. Local area networks (LANs) connect computers that are physically close. They evolved from the early links to peripheral devices such as terminals and printers.

As cheap PCs and local networks became increasingly commonplace in 1980s offices, fierce competition flared among rival standards—with Ethernet eventually dominating.


Invent the “office of the future.” That was the assignment at Xerox’s Palo Alto Research Center (PARC) in 1970. Its research revolved around groundbreaking personal computers called Altos, connected to peripherals and each other through local networks.

How would they connect? ARPANET alumnus Bob Metcalfe provided the answer.

Familiar with ALOHANET, a pioneering digital radio network, Metcalfe realized he could adapt that radio-based model to cables. This simplified the challenge by treating cables as a passive medium, like the air (“ether”) between radio stations. David Boggs and others helped Metcalfe create “Ethernet”.

Local Area Warfare

Ethernet was a system for establishing local networks—but not the only system.

There were academic systems such as England’s Cambridge Ring. Commercial rivals included IBM’s Token Ring and Datapoint’s ARCNET. These all used a model in which computers circulated “tokens” that controlled which machine could send data. Competition also came from the telecommunications industry, as business telephone systems began adding data capabilities.

In 1979, Ethernet creator Bob Metcalfe left Xerox and co-founded 3Com, successfully convincing Digital Equipment Corporation, Intel, and Xerox to back Ethernet as a standard.

Network Operating Systems

Protocols like Ethernet established low-level links between computers. But users still needed to do higher-level tasks, such as sending e-mail, exchanging files, and sharing printers.

This yielded a hodge-podge of third party “network operating systems,” including Novell Netware, and built-in solutions like Apple’s AppleTalk. Eventually, Internet protocols replaced them all.

The Web

Connecting People

Networks connect computers to each other. But how do people use those connections?

Information systems like the Web let us share content such as text, pictures, or music. The Web running over the Internet has become our global commons, absorbing older media—from video to books and telephone calls—and transforming how we work, buy, and stay in touch.

Navigating Information

Ever since the earliest hunter-gatherer asked a neighbor where to pick the best berries, humans have shared—and searched for—information.

Originally, people talked. You asked a question; you got an answer. But when people began storing information as writing, it was sometimes hard to find things.

One answer was to organize information by subject. Another was to create cross-references, like indexes and tables of contents.

As printed knowledge grew, tools for navigating it were critical for enabling the scientific revolution. Today the Web provides us an unprecedented knowledge navigation tool. What revolution will it enable?

Navigating Information with Computers

A Web-like system for organizing information must be a fantastic idea. After all, it’s been invented at least a dozen times since the microfilm-based Memex of the 1940s.

Some systems garnered millions of users and billions of dollars. Some didn’t. But only one, the World Wide Web, ultimately prevailed.

Linking Knowledge

Information systems based on paper and microfilm were enormously difficult and expensive to build. In the 1950s, Ted Nelson and Douglas Engelbart independently suggested using computers instead.

They “computerized” the concept of cross-references, creating the clickable link we use on the Web. Nelson called it a “hyperlink,” and the computerized text “hypertext.”

Nelson and Engelbart both envisioned multi-user systems embracing elements of networking. They, and graphics pioneer Andries van Dam, developed many core computing functions such as word processing, remote collaboration, and elements of the graphical user interface.

The Secret History of Hypertext

“Click here.” Today’s hyperlink is a brilliant breakthrough from the 1960s. Hopping between linked pages is what lets us “surf” the Web instead of plodding through it. Yet hypertext virtually disappeared for 20 years, and was so obscure that the father of the Web may have unknowingly re-invented it in 1980.

Hypertext’s inventors – and some true believers – kept using it, but mostly in academic applications, or for specialized clients like the military. Most people weren’t aware of hypertext until commercial systems like Apple’s HyperCard in the late 1980s. And, later, the Web.

Communicating Through Computers

Computer users began communicating and forming communities as soon as they were linked through timesharing systems in the 1960s. They had realtime chat, person-to-person e-mail, and public discussion groups.

Online systems have added many other tricks since, from publishing to virtual worlds. Yet the earliest forms of communication still thrive, and remain the foundation of online communities.

Online Communities

We’ve been sending electronic messages for over 150 years, starting with telegrams. Computers are just the latest tool.

Computer-based communities have roots in chat among 1800s telegraph operators, who once even conducted a long-distance wedding.

The 1960s timesharing systems pioneered messaging and discussion boards. As computers were networked in the 1970s, academic communities like Usenet multiplied, and email exploded. Community Memory in 1973 was an early forum for non-techies. Later, mass-market online services like AOL, CompuServe, and France’s Minitel united millions, paving the way for today’s Web-based discussion lists, social networking sites, and virtual worlds.

Walled Gardens

By the 1980s, tens of millions worldwide were using networked information systems. But most of these were “walled gardens” with separated communities of users.

Some were limited to subscribers; others divided nationally or by computer skills. Their astonishing variety created a laboratory for Web features now commonplace…and others still awaiting adoption.

Europe and the First Mass-Market “Webs”

In 1971, a team at the BBC, and Sam Fedida at the British Post Office, independently developed Web-like information systems that used ordinary TVs.

The BBC system broadcast data on an unused portion of the TV signal, and evolved into the Teletext information service.

The Post Office’s videotex standard used phone lines, and had high ambitions for broad-reaching uses like today’s Web. It became the foundation of England’s Prestel and France’s wildly successful Minitel. But despite efforts in the U.S., Canada, and Europe, videotex-like systems fizzled outside France.

Minitel and Teletext: Long-Running Successes

Free! That’s always a successful way to attract customers. In 1981, France Telecom offered free Minitel terminals, launching the first mass “Web.” It had tens of millions of users by the 1990s.

In 1974, ad-funded Teletext systems let European TV viewers “surf” pages of news, weather, sports, financial data, and more.

Specialized Systems for Specialized Users

As networked computers arrived in offices through the 1970s and 1980s, specialized information systems blossomed.

LEXIS provided access to legal cases. NEXIS added a database of news articles. There were industrial purchasing systems based on “Electronic Data Interchange” standards for computerized transactions.

Academics and geeks continued expanding “techie” online communities like Usenet (a message board started in 1980 by Duke University students) and Bitnet (a network for file and email exchange).

The Web’s Competitors

The Internet connected millions by 1990. But partly because of non-commercial roots, it lacked user-friendly information systems.

That unmet need inspired global efforts to create such systems, ranging from commercial ventures like WAIS to one-man projects like Viola. Several used clickable hypertext links – including one small experiment ambitiously called the “WorldWideWeb.”

Inventing the Web

At the world’s biggest physics laboratory, CERN in Switzerland, English programmer and physicist Tim Berners-Lee submitted two proposals for what became the Web. Neither was approved. He proceeded anyway.

With only unofficial support from his boss and interested coworkers, he created “WorldWideWeb” on an advanced NeXT computer in 1990. It featured a server, HTML, URLs, and the first browser.

That browser also functioned as an editor—like a word processor connected to the Internet – which reflected his original vision that the Web also incorporate authoring and personal organization tools.

The Web + Internet = Success

By 1989, the Internet was winning over major competitors like OSI, becoming the de facto networking standard.

Within five years, the World Wide Web would similarly prevail over a dozen rival information systems—partly by virtue of its strengths, partly by incorporating rivals.

The two together, the Web running over the Internet, swept the world and changed all of our lives.

Why Did the Web Win?

The Web was one networked information system among many. Why did it triumph?

Several factors contributed. First, the Web was designed to spread virally, requiring no big up-front investment of time and money. It worked on different kinds of computers, and could handle existing data— both legacies of its birth in the international bazaar of CERN. For many people, its simple, easily implemented hypertext links were a key attraction.

The Web also triumphed by absorbing potential rivals, adding support for WAIS and Gopher. Lynx and Viola converted themselves into Web browsers.

Online Services vs. the Web

Most of the big ”walled gardens” — CompuServe, AOL, Minitel in France—resisted the Web and Internet. They either faded out or ended up as Web sites.

Microsoft Network (MSN) might have mounted a serious challenge. But by 1995 the Web was growing quickly, so Microsoft switched course and instead competed on the Web.

Gopher’s Challenge

Gopher, which organized content in folders rather than clickable links, was the Web’s most direct Internet competitor. Educational institutions embraced Gopher, as did the U.S. Congress.

The Web surpassed it partly by incorporating the ability to read Gopher pages. And thanks to a lucky break: the University of Minnesota began charging for Gopher server licenses.

Browsers: Windows on the Web

The Web’s extraordinary tapestry of images and text are presented to us by web browsers. They are only one component of the Web, along with servers and communications protocols, but they are the most visible.

Whoever writes the dominant browser software decides, by intention or omission, what we can see and do on the Web.

Browsers: The First Wave (1990-1993)

Tim Berners-Lee’s 1990 browser-editor ran on rare NeXT computers. CERN refused to fund other versions. So the Web team invited volunteers to write browsers, and provided code to start with.

Eight responded, creating UNIX, Mac, and PC browsers. Viola and Midas were initially the most popular, eclipsed later by Mosaic. Berners-Lee never regained control of his creation.


Mosaic, the first browser supported by a major institution, started the Web on the road from research project to blockbuster success.

Written by brilliant student Marc Andreessen and UNIX expert Eric Bina at the National Center for Supercomputing Applications, Mosaic was modeled on the Viola and Midas browsers and also used the CERN code library. But unlike others, it was reliable, could be installed by amateurs, and soon added colorful graphics within Web pages instead of as separate windows.

Mosaic spread quickly. NCSA assigned teams to write UNIX, Mac, and PC versions, and servers.

Browser War 1: Netscape vs. Mosaic

Mosaic’s triumph caught Silicon Valley’s attention. In 1994, Jim Clark, founder of Silicon Graphics, recruited Marc Andreessen for a new company. The goal: A “Mosaic killer” browser and server.

The newly formed Netscape hired Eric Bina and much of the Mosaic team, and soon achieved its objective.

Browser War 2: Microsoft vs. Netscape

In 1995 Microsoft stopped challenging the Web with its MSN online service. It set out instead to win on the Web with Internet Explorer (IE), based on a licensed version of Mosaic.

Netscape, fresh from a groundbreaking IPO, was riding high. But IE overtook it by 1998. Netscape was partly reincarnated later as Firefox.

Surfing the Web in the Early 1990s

Between 1991 and 1994 the Web grew from a few mostly scientific Websites into a rich and constantly changing online world, far too big for a single person to keep track of. Sites like Hotwired, the Louvre, and the Honolulu Community college site pushed the limits of what the medium was capable of, both technically and in terms of design. From commercial portals like Global Network Navigator to search engines and online newspapers, there was something for every interest.

Servers: Hidden Engines of the Web

We see the Web through browsers, the programs that show us Web pages. Behind the scenes are servers, networked computers that “serve up” those Web pages to our browsers.

Any computer can act as a server. Commercial racks, like the Google server rack, are the hidden engines of the Web—its unseen but essential infrastructure.

This 1999 Google server rack incorporates many technologies, each the victor in its particular arena from among competing standards. Ethernet ties the rack’s individual boards into a local area network; Internet protocols connect the rack to the larger net; Web server software sends the results to our browsers.

The Network as the Computer

Sun Microsystems championed a cherished dream of networking visionaries: making traditional operating systems, and most applications written for them, irrelevant. Sun’s Java applications would run inside browsers, with little need for conventional Microsoft or Apple software.

Earlier systems—like the 1980s Austrian MUPID, Viola, and General Magic’s Telescript—included similar ideas.

Electronic Commerce

A century before anyone clicked “buy” or filled an online shopping cart, e-commerce had started – on telegraph wires.

Early computer e-commerce was mostly business-to-business: price quotes, order entry, and money transfers. E-commerce came to the average consumer in the 1980s on France’s Minitel, and in the 1990s on the Web.

Remote Shopping

The 1840s telegraph electrified – literally – an already growing market for remote transactions by mail.

Telegrams carried business transactions and price quotes. Stock tickers were perhaps the first dedicated e-commerce machines. Western Union pioneered electric money transfers for consumers in 1871.

In the 1980s, pre-Web networked information systems brought retail showrooms to living rooms, with France’s Minitel leading the charge. Many were friendlier to e-commerce than the early Web, offering micropayments, billing, authentication, and more. Web-based commerce started slowly, but accelerated with dizzying speed.

The Web is Open for Business

Companies were wary. Could commerce prosper in the once anti-commercial Internet created by government and academia?

In 1993, O’Reilly’s pioneering Global Network Navigator portal was running online ads. In 1994, Enterprise Integration Technologies (EIT) founded the CommerceNet consortium to encourage Web commerce, and they demonstrated secure credit-card transactions that year. By 1995 pornography and gambling sites were earning substantial profits.

Netscape’s spectacular IPO, and the success of online shopping sites like Amazon and eBay, finally convinced mainstream business to follow the pioneers into Web commerce.


Letters. Telegrams. Phone calls. Most messaging systems cost something to use, which limits unsolicited correspondence. The Web and Internet were different.

In the mid-1990s, e-mail offered a promoter’s paradise: Free delivery to hundreds of millions of potential customers. With negligible costs, even infinitesimal response rates brought profits.

The Dot Com Boom…and Bust

As users flocked to the Web, the opportunities seemed boundless. Nearly every possible business transaction was implemented on the Web, and every community staked out a place online.

Initial skepticism gave way to experimentation, and then mounting excitement as people began to believe that the old laws of business didn’t apply to this new medium. Nobody wanted to be left behind, fueling a frenzy of business ventures—many built on shaky foundations.

In early 2000, business fundamentals reasserted themselves. In one year, technology stocks lost about 60% of their value.

Marketing the Web

Aside from the gambling and adult sites, many Web companies had no clear business model. The marketing reflected that. Many focused on building name recognition and attracting users, in hopes of attracting additional funding.

Dot Com Winners & Losers

The Web’s potential inflated an extraordinary investment bubble. The bubble burst in 2001.

The bust’s impact was uneven. Some companies, like WebVan, imploded spectacularly. Others hung on. A few, like Amazon, grew.

Companies rethought business models, and startups found it harder to get funding. But the Web’s spread wasn’t stopped.

Gone Phishing

New technologies inspire new crimes.

Over a century ago, swindlers exploited telegraphy for stock and racing fraud. Early computer network crime was mostly exploratory, but the Web’s popularity spawned a criminal industry worth billions of dollars.

The Web and Internet’s strength—their freewheeling, open structure, welcoming all—also makes them vulnerable.

Larry Page and Sergey Brin

Page and Brin met as Stanford graduate students in 1995. They argued constantly but became inseparable friends, sometimes called “larryandsergey” by classmates.

The Internet and Web are about sharing and using information. An important part of that process is finding information, often through search engines like Google.

So Much Information in So Little Time

Rummaging through books for the word “rosebud” might take days. But searching for “rosebud” on the Web—bigger than millions of books—takes under a second.

The Web also transforms the tedious process of looking up cross-references, like “see volume IV page 39.” They’re called clickable links on the Web, and they’re instant.

How Do Searches Find?

Automated “crawler” programs visit every available Web site, creating an index of the words they find. When users search on a word, the engine compares it to that index, ranking results based on nearby words and the number of links.

Searching for Profit

Searching the Web is immensely useful. But is it a profitable business? For a decade, the answer was “no.”

Web search was a perennial money loser. For engines like Lycos, AskJeeves, and later AltaVista and Google, banner ads brought income, but not profits. Then, in 2000 Google turned itself—and the search industry— into the iconic Web triumph by refining GoTo.com’s insight: advertisers would pay to place links near search results where keywords appeared, like “Petco.com” near “kitten”.

An auction feature let advertisers bid on keywords. AdWords, Google’s revenue generator, was born.


Mid-Westerner Larry Page and Russian-born Sergey Brin met as computer science graduate students in the mid-1990s—just as fellow Stanford students Jerry Yang and David Filo were founding Yahoo!

Page proposed ranking Web pages by how often other pages link to them. The Stanford Digital Library Project supported an experimental search engine. Google was born.

Users As Contributors

Whose medium is it? The original Web concept, and many pre-Web systems, included an interactive forum, alive with argument, collaboration, and user contributions. Yet many early Web sites more closely resembled traditional broadcasting, with providers feeding content to passive viewers.

In the early 2000s “Web 2.0” brought back interactivity. Social networking, photo and video sharing sites, blogs, wikis, and other forums began relying on users to generate and shape content. Although most browsers still didn’t support Web page editing, Web 2.0 sites found ways to give users a new voice.

Going Viral

With so many people in so many places connected in real time, the Web became an efficient conduit for memes (“cultural genes”) that swiftly swept the globe, from the silly Hamster Dance, to jokes, fads, rumors, and conspiracy theories.

The same energy was harnessed as “viral marketing” for inexpensive product promotion.

The Medium of All Mediums

The Web has shown an unparalleled ability to absorb other media—first mail and chat, then music, telephony, video, and more.

The steady spread of higher-speed connections has created competing delivery systems for newspapers, radio, TV, and movies. It even – finally! – made the 140-year-old dream of the picture phone a reality.

Getting Online

The Web lived up to its original ambitious name, and is indeed “world wide.” But who uses it, and how, varies.

In Asia, it’s common for people to browse via mobile phone or TV. In the developing world, Internet cafes are central. The Web is global - but specifics are often local.