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The Computer for the 21st Century Specialized elements of hardware and software, connected by wires, radio waves and infrared, will be ubiquitous that no one will notice their presence by Mark Weiser T he most profound technologies is approachable only through complex The idea of integrating computers are those that disappear. They jargon that has nothing to do with the seamlessly into the world at large runs weave themselves into the fabric tasks for which people use computers. counter to a number of present-day of everyday life until they are indistin- The state of the art is perhaps analo- trends. "Ubiquitous computing" in this guishable from it. gous to the period when scribes had to context does not mean just computers Consider writing, perhaps the first know as much about making ink or that can be carried to the beach, jun- information technology. The ability to baking clay as they did about writing. gle or airport. Even the most powerful represent spoken language symbolical- The arcane aura that surrounds per- notebook computer, with access to a ly for long-term storage freed informa- sonal computers is not just a "user in- worldwide information network, still tion from the limits of individual mem- terface" problem. My colleagues and I focuses attention on a single box. By ory. Today this technology is ubiqui- at the Xerox Palo Alto Research Center analogy with writing, carrying a super- tous in industrialized countries. Not think that the idea of a "personal" com- laptop is like owning just one very im- only do books, magazines and newspa- puter itself is misplaced and that the portant book. Customizing this book, pers convey written information, but so vision of laptop machines, dynabooks even writing millions of other books, do street signs, billboards, shop signs and "knowledge navigators" is only a does not begin to capture the real pow- and even graffiti. Candy wrappers are transitional step toward achieving the er of literacy. covered in writing. The constant back- real potential of information technolo- Furthermore, although ubiquitous ground presence of these products of gy. Such machines cannot truly make computers may use sound and video "literacy technology" does not require computing an integral, invisible part of in addition to text and graphics, that active attention, but the information to people's lives. We are therefore trying to does not make them "multimedia com- be transmitted is ready for use at a conceive a new way of thinking about puters." Today's multimedia machine glance. It is difficult to imagine modern computers, one that takes into account makes the computer screen into a de- life otherwise. the human world and allows the com- manding focus of attention rather than Silicon-based information technology, puters themselves to vanish into the allowing it to fade into the background. in contrast, is far from having become background. Perhaps most diametrically opposed part of the environment. More than 50 to our vision is the notion of virtual re- million personal computers have been S uch a disappearance is a funda- ality, which attempts to make a world sold, and the computer nonetheless re- mental consequence not of tech- inside the computer. Users don special mains largely in a world of its own. It nology but of human psycholo- goggles that project an artificial scene gy. Whenever people learn something onto their eyes; they wear gloves or sufficiently well, they cease to be aware even bodysuits that sense their mo- of it. When you look at a street sign, tions and gestures so that they can MARK WEISER is head of the Comput- er Science Laboratory at the Xerox Palo for example, you absorb its informa- move about and manipulate virtual ob- Alto Research Center. He is working on tion without consciously performing jects. Although it may have its purpose the next revolution of computing after the act of reading. Computer scientist, in allowing people to explore realms workstations, variously known as ubiqui- economist and Nobelist Herbert A. Si- otherwise inaccessible-the insides of tous computing or embodied virtuality. mon calls this phenomenon "compil- cells, the surfaces of distant planets, the Before working at PARC, he was a profes- ing"; philosopher Michael Polanyi calls information web of data bases-virtu- sor of computer science at the University it the "tacit dimension"; psychologist al reality is only a map, not a territo- of Maryland; he received his Ph.D. from the University of Michigan in 1979. Weis- J. J. Gibson calls it "visual invariants"; ry. It excludes desks, offices, other peo- er also helped found an electronic pub- philosophers Hans Georg Gadamer and ple not wearing goggles and bodysuits, lishing company and a video arts compa- Martin Heidegger call it the "horizon" weather, trees, walks, chance encoun- ny and claims to enjoy computer pro- and the "ready-to-hand"; John Seely ters and, in general, the infinite rich- gramming "for the fun of it." His most Brown of PARC calls it the "periphe- ness of the universe. Virtual reality fo- recent technical work involved the imple- ry." All say, in essence, that only when cuses an enormous apparatus on simu- mentation of new theories of automatic things disappear in this way are we lating the world rather than on invisibly computer memory reclamation, known freed to use them without thinking and enhancing the world that already exists. in the field as garbage collection. so to focus beyond them on new goals. Indeed, the opposition between the 94 SCIENTIFIC AMERICAN September 1991PARC NEWS of UBIQUITOUS COMPUTING begins to emerge in the form of live and integrating them with other tools has helped researchers boards that replace chalkboards as well as in other devices at understand better the eventual shape of ubiquitous comput- the Xerox Palo Alto Research Center. Computer scientists ing. In conjunction with active badges, live boards can cus- gather around a live board for discussion. Building boards tomize the information they display. SCIENTIFIC AMERICAN September 1991 95PAD RADIO FREQUENCY INFRARED RADIO FREQUENCY INFRARED TAB WORK- FILE LASER STATION SERVER PRINTER WIRED AND WIRELESS NETWORKS link computers and al- known as pads. Future networks must be capable of support- low their users to share programs and data. The computers ing hundreds of devices in a single room and must also cope pictured here include conventional terminals and file serv- with devices-ranging from tabs to laser printers or large- ers, pocket-size machines known as tabs and page-size ones screen displays-that move from one place to another. notion of virtual reality and ubiquitous, fact as well as in metaphor. Already trols, thermostats and clocks, as well as invisible computing is so strong that computers in light switches, thermo- small pieces of paper. Depending on the some of us use the term "embodied stats, stereos and ovens help to acti- room, you may see more than 100 tabs, virtuality" to refer to the process of vate the world. These machines and 10 or 20 pads and one or two boards. drawing computers out of their elec- more will be interconnected in a ubiqui- This leads to our goal for initially de- tronic shells. The "virtuality" of com- tous network. As computer scientists, ploying the hardware of embodied virtu- puter-readable data-all the different however, my colleagues and I have fo- ality: hundreds of computers per room. ways in which they can be altered, pro- cused on devices that transmit and dis- Hundreds of computers in a room cessed and analyzed-is brought into play information more directly. We have could seem intimidating at first, just the physical world. found two issues of crucial importance: as hundreds of volts coursing through location and scale. Little is more basic wires in the walls once did. But like the H ow do technologies disappear to human perception than physical jux- wires in the walls, these hundreds of into the background? The van- taposition, and ubiquitous comput- computers will come to be invisible to ishing of electric motors may ers must know where they are. (Today's common awareness. People will simply serve as an instructive example. At the computers, in contrast, have no idea use them unconsciously to accomplish turn of the century, a typical workshop of their location and surroundings.) If a everyday tasks. or factory contained a single engine computer knows merely what room it Tabs are the smallest components of that drove dozens or hundreds of dif- is in, it can adapt its behavior in sig- embodied virtuality. Because they are ferent machines through a system of nificant ways without requiring even a interconnected, tabs will expand on the shafts and pulleys. Cheap, small, effi- hint of artificial intelligence. usefulness of existing inch-scale com- cient electric motors made it possible Ubiquitous computers will also come puters, such as the pocket calculator first to give each tool its own source of in different sizes, each suited to a and the pocket organizer. Tabs will motive force, then to put many motors particular task. My colleagues and I also take on functions that no comput- into a single machine. have built what we call tabs, pads and er performs today. For example, com- A glance through the shop manual boards: inch-scale machines that ap- puter scientists at PARC and other re- of a typical automobile, for example, proximate active Post-it notes, foot-scale search laboratories around the world reveals 22 motors and 25 solenoids. ones that behave something like a sheet have begun working with active badg- They start the engine, clean the wind- of paper (or a book or a magazine) and es-clip-on computers roughly the size shield, lock and unlock the doors, and yard-scale displays that are the equiva- of an employee I.D. card, first devel- so on. By paying careful attention, the lent of a blackboard or bulletin board. oped by the Olivetti Cambridge research driver might be able to discern when- How many tabs, pads and board-size laboratory. These badges can identify ever he or she activated a motor, but writing and display surfaces are there themselves to receivers placed through- there would be no point to it. in a typical room? Look around you: out a building, thus making it possible Most computers that participate in at the inch scale, include wall notes, to keep track of the people or objects embodied virtuality will be invisible in titles on book spines, labels on con- to which they are attached. 98 SCIENTIFIC AMERICAN September 1991In our experimental embodied vir- time. In 20 years computer screens number of purposes: in the home, vid- tuality, doors open only to the right have not grown much larger. Computer eo screens and bulletin boards; in the badge wearer, rooms greet people by window systems are often said to be office, bulletin boards, white boards or name, telephone calls can be automati- based on the desktop metaphor-but flip charts. A board might also serve as cally forwarded to wherever the recipi- who would ever use a desk only nine an electronic bookcase from which one ent may be, receptionists actually know inches high by 11 inches wide? might download texts to a pad or tab. where people are, computer terminals Pads, in contrast, use a real desk. For the time being, however, the ability retrieve the preferences of whoever is Spread many electronic pads around on to pull out a book and place it comfort- sitting at them, and appointment di- the desk, just as you spread out papers. ably on one's lap remains one of the aries write themselves. The automatic Have many tasks in front of you, and many attractions of paper. Similar ob- diary shows how such a simple task as use the pads as reminders. Go beyond jections apply to using a board as a knowing where people are can yield the desk to drawers, shelves, coffee ta- desktop; people will have to become complex dividends: meetings, for ex- bles. Spread the many parts of the many accustomed to having pads and tabs ample, consist of several people spend- tasks of the day out in front of you to on a desk as an adjunct to computer ing time in the same room, and the fit both the task and the reach of your screens before taking embodied virtu- subject of a meeting is most probably arms and eyes rather than to fit the ality any further. the files called up on that room's dis- limitations of glassblowing. Someday Prototype boards, built by Richard play screen while the people are there. pads may even be as small and light as Bruce and Scott Elrod of PARC, are in No revolution in artificial intelligence is actual paper, but meanwhile they can use at several Xerox research laborato- needed, merely computers embedded fulfill many more of paper's functions ries. They measure about 40 by 60 in the everyday world. than can computer screens. inches and display 1,024 768 black- My colleague Roy Want has designed Yard-size displays (boards) serve a and-white pixels. To manipulate the a tab incorporating a small display that can serve simultaneously as an active badge, calendar and diary. It will also act as an extension to computer screens: in- The Active Badge stead of shrinking a program window T his harbinger of inch-scale down to a small icon on the screen, for computers contains a small example, a user will be able to shrink microprocessor and an infrared the window onto a tab display. This will transmitter. The badge broad- leave the screen free for information casts the identity of its wearer and also let people arrange their com- and so can trigger automatic puter-based projects in the area around doors, automatic telephone for- their terminals, much as they now ar- warding and computer displays range paper-based projects in piles on customized to each person read- Chris Kent desks and tables. Carrying a project to ing them. The active badge and PARC a different office for discussion is as other networked tiny computers simple as gathering up its tabs; the as- are called tabs. sociated programs and files can be called up on any terminal. T he next step up in size is the pad, something of a cross be- tween a sheet of paper and cur- rent laptop and palmtop computers. Robert Krivacic of PARC has built a BATTERIES prototype pad that uses two micro- processors, a workstation-size display, a multibutton stylus and a radio net- work with enough communications bandwidth to support hundreds of de- vices per person per room. Pads differ from conventional por- table computers in one crucial way. CONTROL Whereas portable computers go every- BUTTON MICRO- where with their owners, the pad that PROCESSOR must be carried from place to place is a failure. Pads are intended to be "scrap computers" (analogous to scrap paper) that can be grabbed and used anywhere; they have no individualized identity or importance. One way to think of pads is as an anti- INFRARED LIGHT-EMITTING dote to windows. Windows were invent- DIODES ed at PARC and popularized by Apple in the Macintosh as a way of fitting sev- eral different activities onto the small space of a computer screen at the same SCIENTIFIC AMERICAN September 1991 99display, users pick up a piece of wire- and so understand a world in which a pleasant and effective "place" to get less electronic "chalk" that can work computer interaction informally en- things done. either in contact with the surface or hances every room. Live boards can What will be most pleasant and effec- from a distance. Some researchers, us- usefully be shared across rooms as tive is that tabs can animate objects ing themselves and their colleagues as well as within them. In experiments previously inert. They can beep to help guinea pigs, can hold electronically me- instigated by Paul Dourish of Euro- locate mislaid papers, books or other diated meetings or engage in other PARC and Sara Bly and Frank Halasz items. File drawers can open and show forms of collaboration around a live of PARC, groups at widely separated the desired folder-no searching. Tabs board. Others use the boards as test- sites gathered around boards-each in library catalogues can make active beds for improved display hardware, displaying the same image-and jointly maps to any book and guide searchers new "chalk" and interactive software. composed pictures and drawings. They to it, even if it is off the shelf, left on a For both obvious and subtle rea- have even shared two boards across table by the last reader. sons, the software that animates a the Atlantic. In presentations, the size of text on large shared display and its electron- Live boards can also be used as bul- overhead slides, the volume of the am- ic chalk is not the same as that for a letin boards. There is already too much plified voice, even the amount of am- workstation. Switching back and forth text for people to read and compre- bient light, can be determined not by between chalk and keyboard may in- hend all of it, and Marvin Theimer guesswork but by the desires of the lis- volve walking several steps, and so the and David Nichols of PARC have built a teners in the room at that moment. act is qualitatively different from using prototype system that attunes its pub- Software tools for tallying votes in- a keyboard and mouse. In addition, lic information to the people reading it. stantly and consensus checking are al- body size is an issue. Not everyone can Their "scoreboard" requires little or no ready available in electronic meeting reach the top of the board, so a Macin- interaction from the user other than to rooms of some large corporations; tabs tosh-style menu bar might have to run look and to wear an active badge. can make them widespread. across the bottom of the screen instead. Prototype tabs, pads and boards are We have built enough live boards just the beginning of ubiquitous com- to permit casual use: they have been puting. The real power of the concept T he technology required for ubiq- uitous computing comes in three placed in ordinary conference rooms comes not from any one of these de- parts: cheap, low-power comput- and open areas, and no one need sign vices-it emerges from the interaction ers that include equally convenient dis- up or give advance notice before us- of all of them. The hundreds of proces- plays, software for ubiquitous appli- ing them. By building and using these sors and displays are not a "user inter- cations and a network that ties them boards, researchers start to experience face" like a mouse and windows, just all together. Current trends suggest that COMPUTER SCRATCHPADS augment the conventional screen type pads are wired to conventional computers; thus far only in this office at the Xerox Palo Alto Research Center. Proto- a handful of wireless models have been built. 100 SCIENTIFIC AMERICAN September 1991the first of these requirements will eas- files virtually unnecessary, for example. ily be met. Flat-panel displays contain- Although processors and displays ing 480 black-and-white pixels should be capable of offering ubiqui- are now common. This is the standard tous computing by the end of the dec- size for PCs and is also about right ade, trends in software and network for television. As long as laptop, palm- technology are more problematic. Cur- top and notebook computers continue rent implementations of "distributed to grow in popularity, display prices computing" simply make networked will fall, and resolution and quality file servers, printers or other devic- will rise. By the end of the decade, a es appear as if they were connected 1,000 800-pixel high-contrast display directly to each user's computer. This will be a fraction of a centimeter thick approach, however, does nothing to ex- and weigh perhaps 100 grams. A small ploit the unique capabilities of physi- battery will provide several days of con- cally dispersed computers and the in- tinuous use. formation embodied in knowing where Larger displays are a somewhat dif- a particular device is located. ferent issue. If an interactive computer screen is to match a white board in usefulness, it must be viewable from C operating systems and window-based display software arm's length as well as from across a will have to change substantial- room. For close viewing, the density of ly. The design of current operating sys- picture elements should be no worse items, such as DOS and Unix, is based than on a standard computer screen, on the assumption that a computer's about 80 per inch. Maintaining a densi- hardware and software configuration ty of 80 pixels per inch over an area will not change substantially while it is RADIO TRANSCEIVER links pads and several feet on a side implies display- running. This assumption is reasonable other movable computer devices to the ing tens of millions of pixels. The big- wired network. This unit, intended to for conventional mainframes and per- gest computer screen made today has be mounted on the ceiling, contains an- sonal computers, but it makes no sense only about one fourth that capacity. tennas in its crossed arms and two light- in terms of ubiquitous computing. emitting diodes to signal its status. Such large displays will probably be ex- Pads, tabs and even boards may come pensive, but they should certainly be and go at any time in any room, and available. it will certainly be impossible to shut ity. Making pads, tabs and boards work The large display will require ad- down all the computers in a room to together seamlessly will require chang- vanced microprocessors to feed it. Cen- install new software in any one of es in the kinds of protocols by which tral-processing-unit speeds reached a them. (Indeed, it may be impossible to applications programs and their dis- million instructions per second in 1986 find all the computers in a room.) played windows communicate. and continue to double each year. Some One solution may be "micro-ker- The network that will connect ubiq- industry observers believe that this ex- nel" operating systems such as those uitous hardware and software poses ponential growth in raw chip speed may developed by Rick Rashid of Carne- further challenges. Data transmission begin to level off about 1994 but that gie Mellon University and A. S. Tanen- rates for both wired and wireless net- other measures of performance, includ- baum of Vrije University in Amster- works are increasing rapidly. Access to ing power consumption and auxiliary dam. These experimental systems con- gigabit-per-second wired nets is already functions, will still improve. The 100- tain only the barest scaffolding of fixed possible, although expensive, and will gram flat-panel display, then, might be computer code; software modules to become progressively cheaper. (Giga- driven by a microprocessor that exe- perform specific functions can be read- bit networks will seldom devote all cutes a billion operations per second ily added or removed. Future operat- of their bandwidth to a single data and contains 16 megabytes of on-board ing systems based on this principle stream; instead they will allow enor- memory along with sound, video and could shrink and grow automatically to mous numbers of lower-speed trans- network interfaces. Such a processor fit the changing needs of ubiquitous missions to proceed simultaneously.) would draw, on average, a few percent computation. Small wireless networks, based on dig- of the power required by the display. Current window display systems also ital cellular telephone principles, cur- Auxiliary storage devices will aug- are not ready to cope with ubiqui- rently offer data rates between two and ment main memory capacity: conserva- tous computing. They typically assume 10 megabits per second over a range tive extrapolation of current technol- that a particular computer will display of a few hundred meters. Low-pow- ogy suggests that removable hard disks all the information for a single appli- er wireless networks capable of trans- (or nonvolatile memory chips) the size cation. Although the X Window Sys- mitting 250,000 bits per second to of a matchbook will store about 60 tem and Windows 3.0, for example, can each station will eventually be available megabytes each. Larger disks contain- cope with multiple screens, they do commercially. ing several gigabytes of information not do well with applications that start Yet the problem of transparently will be standard, and terabyte storage- out on one screen and move to anoth- linking wired and wireless networks roughly the data content of the Library er, much less those that peregrinate of Congress-will be common. Such resists solution. Although some stop- from computer to computer or room gap methods have been developed, en- enormous stores will not necessarily to room. gineers must develop new communi- be filled to capacity with usable infor- Solutions to this problem are in their cations protocols that explicitly rec- mation. Abundant space will, however, infancy. Certainly no existing display ognize the concept of machines that allow radically different strategies of system can perform well while working move in physical space. Furthermore, information management. A terabyte with the full diversity of input and out- the number of channels envisioned in of disk storage will make deleting old put forms required by embodied virtual- most wireless network schemes is still SCIENTIFIC AMERICAN September 1991 101KEY COMPONENTS OF UBIQUITOUS COMPUTING are the pads and tabs under de- velopment at the Xerox Palo Alto Research Center. The page-size pad (top, exterior and interior views) contains two microprocessors, four million bytes of random-ac- PARC TAB cess memory, a high-speed radio link, a high-resolution pen interface and a black- and-white display that is 1,024 by 768 pixels. Because it uses standard window system software, the pad can communicate with most workstations. The much smaller tab (at left), by 31/4 inches, has three control buttons, a pen interface, audio and an infrared link for communicating throughout a room. The author be- lieves future homes and offices will contain hundreds of these tiny computers. minutes ago her alarm clock, alerted missing manual will find itself. In the by her restless rolling before waking, garage, she tracks a beeping noise to had quietly asked, "Coffee?" and she where the oil-stained manual had fallen had mumbled, "Yes." "Yes" and "no" behind some boxes. Sure enough, there are the only words it knows. is the tiny tab the manufacturer had very small, and the range large (50 Sal looks out her windows at her affixed in the cover to try to avoid E- to 100 meters), that the total num- neighborhood. Sunlight and a fence are mail requests like her own. ber of mobile devices is severely lim- visible through one, and through oth- On the way to work Sal glances in ited. The ability of such a system to ers she sees electronic trails that have the foreview mirror to check the traf- support hundreds of machines in ev- been kept for her of neighbors coming fic. She spots a slowdown ahead and ery room is out of the question. Sin- and going during the early morning. also notices on a side street the telltale gle-room networks based on infrared Privacy conventions and practical data green in the foreview of a food shop, or newer electromagnetic technologies rates prevent displaying video footage, and a new one at that. She decides to have enough channel capacity for ubiq- but time markers and electronic tracks take the next exit and get a cup of cof- uitous computers, but they can work on the neighborhood map let Sal feel fee while avoiding the jam. only indoors. cozy in her street. Once Sal arrives at work, the fore- Present technologies would require a Glancing at the windows to her kids' view helps her find a parking spot mobile device to have three different rooms, she can see that they got up 15 quickly. As she walks into the building, network connections: tiny-range wire- and 20 minutes ago and are already in the machines in her office prepare to less, long-range wireless and very high the kitchen. Noticing that she is up, log her in but do not complete the se- speed wired. A single kind of network they start making more noise. quence until she actually enters her of- connection that can somehow serve all At breakfast Sal reads the news. She fice. On her way, she stops by the of- three functions has yet to be invented. still prefers the paper form, as do most fices of four or five colleagues to ex- people. She spots an interesting quote change greetings and news. either an explication of the prin- from a columnist in the business sec- N Sal glances out her windows: a gray ciples of ubiquitous comput- tion. She wipes her pen over the news- day in Silicon Valley, 75 percent humidi- ing nor a list of the technolo- paper's name, date, section and page ty and 40 percent chance of afternoon gies involved really gives a sense of number and then circles the quote. The showers; meanwhile it has been a quiet what it would be like to live in a world pen sends a message to the paper, morning at the East Coast office. Usually full of invisible widgets. Extrapolating which transmits the quote to her office. the activity indicator shows at least one from today's rudimentary fragments Electronic mail arrives from the com- spontaneous, urgent meeting by now. of embodied virtuality is like trying to pany that made her garage door open- She chooses not to shift the window on predict the publication of Finnegans er. She had lost the instruction manual the home office back three hours-too Wake shortly after having inscribed the and asked them for help. They have much chance of being caught by sur- first clay tablets. Nevertheless, the ef- sent her a new manual and also some- prise. But she knows others who do, fort is probably worthwhile: thing unexpected-a way to find the usually people who never get a call from old one. According to the note, she can the East but just want to feel involved. Sal awakens; she smells coffee. A few press a code into the opener and the The telltale by the door that Sal pro- 102 SCIENTIFIC AMERICAN September 1991grammed her first day on the job is bly into people's lives, this scenario gymnastics, it will transform what is ap- blinking: fresh coffee. She heads for points up some of the social issues parently possible. Desktop publishing, the coffee machine. that embodied virtuality will engender. for example, is essentially no different Coming back to her office, Sal picks Perhaps key among them is privacy: from computer typesetting, which dates up a tab and "waves" it to her friend hundreds of computers in every room, back to the mid-1960s. But lease of use Joe in the design group, with whom all capable of sensing people near them makes an enormous difference. she has a joint assignment. They are and linked by high-speed networks, When almost every object either con- sharing a virtual office for a few weeks. have the potential to make totalitarian- tains a computer or can have a tab at- The sharing can take many forms-in ism up to now seem like sheerest anar- tached to it, obtaining information will this case, the two have given each other chy. Just as a workstation on a local- be trivial: "Who made that dress? Are access to their location detectors and area network can be programmed to there any more in the store? What was to each other's screen contents and lo- intercept messages meant for others, the name of the designer of that suit cation. Sal chooses to keep miniature a single rogue tab in a room could po- I liked last week?" The computing en- versions of all Joe's tabs and pads in tentially record everything that hap- vironment knows the suit you looked view and three-dimensionally correct in pened there. at for a long time last week because it a little suite of tabs in the back corner Even today the active badges and self- knows both of your locations, and it of her desk. She can't see what any- writing appointment diaries that offer can retroactively find the designer's thing says, but she feels more in touch all kinds of convenience could be a name even though that information did with his work when noticing the dis- source of real harm in the wrong hands. not interest you at the time. plays change out of the corner of her Not only corporate superiors or under- Sociologically, ubiquitous computing eye, and she can easily enlarge any- lings but also overzealous government may mean the decline of the computer thing if necessary. officials and even marketing firms could addict. In the 1910s and 1920s many A blank tab on Sal's desk beeps and make unpleasant use of the same infor- people "hacked" on crystal sets to take displays the word "Joe" on it. She picks mation that makes invisible computers advantage of the new high-tech world it up and gestures with it toward her so convenient. of radio. Now crystal-and-cat's-whis- I live board. Joe wants to discuss a docu- Fortunately, cryptographic techniques ker receivers are rare because high- ment with her, and now it shows up on already exist to secure messages from quality radios are ubiquitous. In ad- 1 the wall as she hears Joe's voice: one ubiquitous computer to another dition, embodied virtuality will bring "I've been wrestling with this third and to safeguard private information computers to the presidents of indus- paragraph all morning, and it still has stored in networked systems. If de- tries and countries for nearly the first e the wrong tone. Would you mind read- signed into systems from the outset, time. Computer access will penetrate ing it?" these techniques can ensure that private all groups in society. a Sitting back and reading the para- data do not become public. A well-im- Most important, ubiquitous comput- graph, Sal wants to point to a word. She plemented version of ubiquitous com- ers will help overcome the problem gestures again with the "Joe" tab onto a of information overload. There is more I puting could even afford better privacy nearby pad and then uses the stylus to protection than exists today. information available at our fingertips circle the word she wants: during a walk in the woods than in any "I think it's this term It's just not in common enough use and B y pushing computers into the computer system, yet people find a walk background, embodied virtuality among trees relaxing and computers y makes the whole passage sound a little will make individuals more aware frustrating. Machines that fit the human formal. Can we rephrase the sentence of the people on the other ends of their environment instead of forcing humans a to get rid of it?" computer links. This development may to enter theirs will make using a com- "I'll try that. Say, by the way, Sal, did reverse the unhealthy centripetal forc- puter as refreshing as taking a walk in you ever hear from Mary Hausdorf?" es that conventional personal comput- the woods. 1 "No. Who's that?" ers have introduced into life and the "You remember. She was at the meet- workplace. p ing last week. She told me she was go- Even today, people holed up in win- FURTHER READING ing to get in touch with you." dowless offices before glowing comput- er screens may not see their fellows for THE TACIT DIMENSION. Michael Polanyi. r Sal doesn't remember Mary, but she Doubleday & Company, 1966. does vaguely remember the meeting. the better part of each day. And in vir- TOWARD PORTABLE IDEAS. Mark Stefik and She quickly starts a search for meet- tual reality, the outside world and all John Seely Brown in Technological Sup- ings held during the past two weeks its inhabitants effectively cease to exist. port for Work Group Collaboration. Edit- with more than six people not previ- Ubiquitous computers, in contrast, re- ed by Margrethe H. Olson. Lawrence Erl- V ously in meetings with her and finds side in the human world and pose no baum Associates, 1989. the one. The attendees' names pop up, barrier to personal interactions. If any- RECENT DEVELOPMENTS IN OPERATING SYS- and she sees Mary. thing, the transparent connections that Special issue of Computer (IEEE C Computer Society), Vol. 23, No. 5; May As is common in meetings, Mary they offer between different locations 1990. made some biographical information and times may tend to bring communi- n ACTIVITY-BASED INFORMATION RETRIEVAL: about herself available to the other at- ties closer together. TECHNOLOGY IN SUPPORT OF HUMAN tendees, and Sal sees some common My colleagues and I at PARC believe MEMORY. Mik Lamming and William r background. She'll just send Mary a that what we call ubiquitous comput- Newman. Available as Rank Xerox Euro- note and see what's up. Sal is glad Mary ing will gradually emerge as the domi- PARC Technical Report 91-03; February did not make the biography available nant mode of computer access over the 1991. only during the time of the meeting, as next 20 years. Like the personal com- LCDs AND BEYOND. Nick Baran in Byte, Vol. 16, No. 2, pages 229-236; February 1991. many people do puter, ubiquitous computing will pro- A TALK WITH INTEL. Kenneth M. Sheldon duce nothing fundamentally new, but in Byte, Vol. 16, No. 4, pages 131-140; In addition to showing some of the by making everything faster and easier April 1991. ways that computers can enter invisi- to do, with less strain and fewer mental tax Th 104 SCIENTIFIC AMERICAN September 1991