Designing the Star User Interface The Star user interface adheres rigorously to a small set of principles designed to make the system seem friendly by simplifying the human-machine interface. Dr. David Canfield Smith, Charles Irby, Ralph Kimball, and Bill Verplank Xerox Corporation 3333 Coyote Hill Rd. Palo Nto, CA 94304 Eric Harslem Xerox Corporation El Segundo, CA 90245 In April 1981, Xerox announced the work station's network, or on a behind those features and illustrate the 8010 Star Information System, a file server on a different network. the principles with examples. This new personal computer designed for Mailing permits users of work sta- discussion is addressed to the offices. Consisting of a processor, a tions to communicate with one designers of other computer pro- large display, a keyboard, and a another. Printing utilizes laserdriven grams and systems-large and small. cursor-control device (see photo I), it raster printers capable of printing is intended for business professionals both text and graphics. Star Architecture who handle information. As Jonathan Seybold has written, Before describing Star's user inter- Star is a multifunction system com- 'This is a very different product: Dif- face, several essential aspects of the bining document creation, data pro- ferent because it truly bridges word Star architecture should be pointed cessing, and electronic filing, mailing, processing and typesetting functions; out. Without these elements, it would and printing. Document creation in- different because it has a broader have been impossible to design an cludes text editing and formatting, range of capabilities than anything interface anything like the present graphics editing, mathematical for- which has preceded it; and different one. mula editing, and page layout. Data because it introduces to the commer- The Star hardware was modeled processing deals with homogeneous, cial market radically new concepts in after the experimental Xerox Alto relational databases that can be human engineering." (See reference computer (see reference 19). Like sorted, filtered, and formatted under 15.) Alto, Star consists of a Xerox- user control. Filing is an example of a The Star user interface adheres developed, high-bandwidth, MSI network service utilizing the Ethernet rigorously to a small set of design (medium-scale integration) processor; local-area network (see references 9 principles. These principles make the local disk storage; a bit-mapped and 13). Files may be stored on a system seem familiar and friendly, display screen having a 72dots-per- work station's disk, on a file server on simplify the human-machine interac- inch, resolution; a pointing device tion, unify the nearly two dozen func- called the "mouse"; and a connection About the Authors tional areas of Star, and allow user to the Ethernet network. Stars are These five Xerox employees have worked on experience in one area to apply in higher-performance machines than the Star user interface project for the past five others. In reference 17, we presented Altos, being about three times as fast, years. Their academic backgrounds are in com- an overview of the features in Star. having 512K bytes of main memory puter science and psychology. Here, we describe the principles (versus 256K bytes on most Altos), 10 242 A~rill982O BYTE Publications lnc Circle 26 on inquiry card. MODELIII WITH 2DISK DRIVES (UK RAM).............. S17U.06 DRIVE0 INTERNAL Photo 1: A Star work station showing the processor, display, keyboard, and mouse. ' ' DRIVE 2 DRIVE 3 EXTERNAL EXTERNAL 4OTraL sn9.95 .SS.m Photo 2: The Star keyboard and mouse. Note the two buttons on top of thi mouse. or 29 megabytes of disk memory (ver- the user interface is the bit-mapped sus 2.5 megabytes), a 10%- by display screen. Both Star and Alto 13%-inch display screen (versus 10?h devote a portion of main memory to by 8 inches), and a 10-megabits-per- the screen: 100K bytes in Star, 50K second Ethernet (versus 3 megabits). bytes (usually) in Alto. Every screen Typically, Stars, like Altos, are dot can be individually turned on or linked via Ethernets to each other and off by setting or resetting the cor- to shared file, mail, and print servers. responding bit in memory. It should Communication servers connect be obvious that this gives both com- Ethernets to one another either direct- puters an excellent ability to portray ly or over telephone lines, enabling visual images. We believe that all im- internetwork communication. (For a pressive office systems of the future _, detailed description of the Xerox Alto will have bit-mapped displays., computer, see the September 1981 Memory cost will soon be insignifi- -8 BYTE article 'The Xerox Alto Com- cant enough that they will be feasible I + puter" by Thomas A. Wadlow on even in home computers. Visual com- 4 ! page 58.) munication is effective, and it can't be ,!, The most important ingredient of exploited without graphics flexibility. Tiwe must be a way k change network or what anyone else is da- do% on the screen quickly. Star has a ing. Larger programs can be written, high memory bandwidth, about 90 using the disk for swapping. megahertz (MHz).The entire Star The Ethernet lets both ,Stars and screen is repainted from memory 39 Altos have a distributed architecture. times per second, about a 50-MHz Each hachine is connected to an data rate between memory and the Ethernet. Other machines on the screen. This would swamp most com- Ethernet are dedicated as puter memories. However, since "serversn-machines that are at- Star's memory is double-ported, tached to a resource and provide ac- refreshing the display does not ap- cess to that resource. preciably slow down processor memory access. Star also has separate Star Design Methodology logic devoted solely to refreshing the We have learned from Star the im display. Finally, special microcode portance of formulating the fun has been written to assist in changing damental concepts (the user's concep the contents of memory. quickly, per- tual model) before software is writ- mitting a variety of screen processing ten, rather than tacking on a user in- : that would not otherwise be practical terface afterward. Xerox devoted II (see reference 8). about thirty work-years to the design People need a way to quickly point of the Star user interface. It was to items on the screen. Cursor step designed before the functionality of keys are too slow; nor are they the system was fully decided. It was suitable for graphics. Both Star and even designed before the computer Alto use a pointing device called the hardware was built. We worked for mouse (see photo 2). First developed two years before we wrote a single at Stanford Research Institute (see line of actual product software. reference 06), Xerox's version has a Jonathan Seybold put it this way, ball on the bottom that turns as the ''Most system design efforts start with mouse slides over a flat surface such hardware specifications, follow this SITTING as a table. Electrobics sense the ball with a set of functional specifications rotation and guide a cursor on the for the software, then try to fii screen in corresponding motions. The out a logical user interface and com- mouse possesses several important mand structure. The Star project ' PRETTY attribute% started the other way around: the You can use just about any desk for a paramount coniern was to define a computer terminal stand. But with *It is a ''Fitts's law" device, That is, conceptqal model of how the user CF&A, yoli're sitting pretty. Our full rangeaf desks, workstations, and ter- after some practice you can point would relate to the system. Hardware ' mine1 stands are designed to accom- with a mouse as quickly and easily as and software followed from this." modate a variety of computer equip you can with the tip of your finger. (See reference 15.') ment. Choose from our Classic Series The limitations on pointing speed are In fact, before we even began desks, DR Series desks and enclo- those inherent in the human nervous designing the model, we developed a sures, specialtyitems like our Apple11 . desk, or a univeisal piinter stand. system (see references 3 and 7). methodology by which we would do You'll be sitting pretty with attractive .It stays where it was left when you the design. Our methodology report color selections, durable construc- are not touching it. It doesn't have to (see reference 10) stated: tion, versatile configurations, useful be picked up like a light pen or stylus. options, competitive prices, qulczk .It has buttons on top that can be One of the most troublesome and delivery, and personal service. It's our least understood aspects of interactive ,way of doing business. sensed under program control. The buttons let you point to and interact systems is the user interface. In the design of user interfaces, we are con- with objects on the screen in a variety cerned with several issues: the provi- of ways. sion of languages by which users can express their commands to the com- puter; the design of display representa- tions that show the state of the system Computer Furniture and Every Star and Alto has its own Accessories, Inc. hard disk for local storage of pro- to the user; and other more abstract issuesthat affect the user's understand- 1441 West 13-d Street grams and data. This enhances their ing of the system's behavior. Many of Qardena, CA 90249 personal name, providing consistent these issues are highly subjective and (213) 327-7710 accws' to information raardless of are therefore often addressed in an ad how'ntmy.other:ma~bi~esare on the hoc fashion.