Lisa computer retrospective - Part 3 of 7

From: David Craig <dcraig_at_email.domain.hidden>
Date: Thu, 4 Jan 2001 17:30:12 -0700

THE APPLE LISA COMPUTER: A RETROSPECTIVEPART 3 OF 7LISA TECHNOLOGY-------------------------------------------------The Lisa has proven to be one of the most underrated personalcomputer systems in the industry's history. When Appleintroduced the Lisa in 1983, very few people seemed tounderstand the revolutionary concepts implicit in its design. Inretrospect, we can say that Apple itself shared this lack ofunderstanding.Apple's revolutionary "Lisa Technology" combined tightintegration of hardware and software with a simple design goal:to make the computer as easy to use as possible, withoutsacrificing power that would enable the user to accomplishsignificant computing tasks. In Apple's words, Lisa Technologywas based upon "the extensive use of graphics, consistent userinterface, and pointing device (the 'mouse') which togetheremulate the way an individual works in the office".To quote one of Apple's Lisa documents, the Lisa hardware andsoftware combination "must be seen to be believed;" but in factit must be u

sed, extensively, before it can be appreciated.Discussing Lisa's important differences will only bring onskepticism; demonstrating the system is some help, but often nota lot. The non-Lisa user meeting a Lisa for the first time willperennially ask, "Can something that looks so gimmicky really doserious work?" But I think that most people who spend severalhours with a Lisa accomplishing something real -- aside fromthose few who have tried it and really don't like it -- willcome away with positive conclusions about the Lisa's value, orat least the value of its technology.One effective presentation tool used by Apple for Lisa customerswas the Lisa Concept Pyramid. The apex of this pyramidrepresented the solutions required by the target customer, theinformation professional, who was called a "knowledge worker" byApple). The generic applications are all tools which can be usedby almost anyone.The middle layer of the pyramid represented the underlyingtechnology of a truly "easy to use" system. The prototype ofthis  

technology was created within Xerox PARC, but Apple'srefinement of it consumed the bulk of Lisa's 200-man-yeardevelopment effort. Many contributions by Apple wereenhancements of integration and of the user interface; keys tothat accomplishment included the one-button mouse and its driversoftware. Another cornerstone is Visual Fidelity, or thecorrelation between screen image and printed output now referredto as "WYSIWYG."The bottom layer is the foundation for the layers above. Themajor design issues were all dictated by the needs of thesoftware, rather than the traditional domination of the designby hardware. (4) The Lisa operating system needed to be multi-tasking, to allow multiple programs to co-exist on the screen.The Graphics/Mouse technology was the key to making the Lisa'suser interface possible.All Lisa user actions were centered around the one-button mouse.The user moved the mouse pointer (usually a small arrow-shapedpointer) to the screen object of interest. For example, toactivate a menubar command  the user moved the mouse pointer tothe appropriate command group label, e. g. Edit, and pressed themouse button. The selected menu would then "pull down" showing alist of the specific commands the user could work with. Stillholding the mouse button down, the user dragged the mousepointer to the desired command, e. g. Copy, and released themouse button when the mouse arrow touched the Copy command andthe command name in the menu was highlighted. At this point theselected menu command was activated and performed its functionon the selected window object. For example, if you were usingLisaWrite, the Lisa's word processor, you could copy data from aLisaWrite document by first selecting with the mouse pointer thetext to copy, and then activating the Edit menu Copy command.The Lisa's technology has now been copied extensively by othersystems, both within Apple and elsewhere. But in my opinionseveral aspects of the Lisa's design made it unique. Theseaspects have not, so far, been adopted to any significant degreeb y

 other microcomputer systems.SOFT POWER-ON AND POWER-OFF-------------------------------------------------The Lisa was powered on and powered off by a button on the frontplate of the computer case, but its power button was not a true"hard" power switch; a Lisa, once plugged in, was alwaysrunning. When the Lisa was "off" it was really in a low-powermode (what might now be called a sleep mode) that toggled tofull power when the user pressed the power button. Conversely,if the user pressed the power button to turn the Lisa "off," thehardware called to the operating system (really to the LisaDesktop Manager) which commanded all executing programs to savetheir documents. When all programs indicated that they hadcommitted their documents to disk, the Lisa toggled to its low-power mode.SELF-ORGANIZING DESKTOP-------------------------------------------------The Lisa maintained an orderly desktop for the user. At power-down, the Desktop Manager would save the state of the desktop aswell as all open document data. When
 the user powered-up theLisa, the Desktop Manager restored the desktop state as it wason power-down.DOCUMENT-CENTERED VIEW-------------------------------------------------The Lisa supported a document-centered view which gave priorityto documents, not programs. To start a new document in anyapplication, the Lisa user tore off a sheet of "stationery" froma pad icon that resided on the screen. When "opened" by the usera stationery pad automatically duplicated itself, set its nameand the current date, and created a window on-screen for theuser. (Stationery pads survive in Macintosh System 7, but theMacintosh does not use a document-based view.) Lisa programicons rarely came into play except to move the program file toanother disk. Generally, Lisa users kept document stationerypads easily accessible on the screen and kept program icons in afolder, which they opened only to add new programs or delete oldones.RELIABLE FILE DATA STORAGE-------------------------------------------------Several design decisions made t

h
e Lisa's file system unusuallyreliable. To reduce the impact of a system crash, the filesystem maintained distributed redundant information about thefiles, in different forms and in different places on disk media.For example, information about a file in the central diskcatalog was repeated in a special disk block at the head of thatfile. Also, each block on the disk specified the part of thefile to which it belonged, in a special string called a "blocktag." Since all files and blocks on a disk were able to identifyand describe themselves, there were several ways to recover lostinformation. A utility called the Scavenger was able toreconstruct damaged disk catalogs from the redundant informationstored in and about each file.The Scavenger is activated automatically whenever the Lisadetermines that a disk has problems. At this point the Lisa'slow-level operating system informs the Desktop Manager, whichdisplays a dialog for the user. The user may elect to have theLisa repair the disk or eject it. In my experien

ces with theLisa I've only had one disk that the Scavenger could not fix.The Lisa's ProFile hard disk and Twiggy floppy drives alsoincluded extensive reliability features. One such feature wasdisk block sparing. When a disk block (of 512 bytes) wasdetected as beginning to fail, the Lisa's disk drive (whetherProFile or Twiggy) moved the data to a spare area of the diskand marked the failing block as "bad". Whenever a programattempted to access a bad block, the drive automaticallysubstituted a "spared" data block.The original Macintosh supported block tags at the hardwarelevel, but Apple never provided a Mac Scavenger program tomonitor and use these tags. Neither did Apple's Finder program(the Desktop Manager equivalent for the Mac) support checks forfailing disk blocks. After several years Apple abandoned diskblock tag use. Newer Macintoshes have introduced block sparingfor high density floppies and hard drives.UNIQUE SYSTEM SERIAL NUMBERS-------------------------------------------------Each Lisa contained a 

u
nique serial number, stored in a specialelectronic chip, which the Desktop Manager could read. The Lisaused the serial number for program protection, and to establishuniquely identified communication nodes within Lisa datanetworks.END OF PART 3

> Regards,
> David T. Craig
>
> ###########################################################
> # David T. Craig -- CyberWolf Inc. -- ACI 4D Developer #5
> # Aspen Plaza, 1596 Pacheco, Suite 203
> # Santa Fe, NM 87505 USA
> # voice 505.983.6463 ext 15 -- fax 505.988.2580
> # dcraig_at_email.domain.hidden
> ###########################################################

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Host your mailing list for free at Maclaunch http://www.maclaunch.com/forms/list.shtml Received on 2001-01-04 16:28:38