The rigid command language syntax and mode based structures of conventional
operating systems may be a thing of the past.
Lisa, an advanced personal computer system, radically changes the way
people interact with a computer. In traditional microcomputer operating
systems, interaction occurs strictly via a special command language. With
Lisa, however, the use of a very intuitive and consistent electronic desktop
model allows interaction through pointing and graphics.
Although traditional operating systems provide a raw capability for general
purpose computing, they are excessively complex, arcane, and difficult to use.
Thus, they do not meet the needs of nonexpert computer users. Nor do these
systems provide all the required functionality since they do not support rapid
switching between simultaneous activities. In addition, the convenient examination
and transfer of data between these interdependent activities are not
supported. Furthermore, existing systems cannot be easily modified.
The Apple’s Local Integrated Software Architecture (Lisa) takes a
revolutionary approach to operating system software, resulting in an
integrated system that is an order of magnitude easier to use. This new
approach, not constrained by the traditional structures of existing operating
systems, is concerned almost exclusively with providing features that make
the computer easier or more convenient for the nonexpert user. With today’s
technology, the difficulty of providing such a feature is minimal. Five
concepts are implicit in Lisa’s operating system. First, Lisa is a
personal computer. As demonstrated by the microcomputer revolution, it is
economically and technically sound to dedicate a single computer to a single
person, rather than forcing many users to share part of a remote computer.
Second, Lisa is intuitive; it works the way people do. Third, Lisa is
consistent; commands are invoked the same way throughout the system and, where
it makes sense, commands apply uniformly throughout the system. Fourth,
Lisa is comprehensive; simultaneous multiple activities can be performed
with easy transfer of information between them. Finally, Lisa is
communicative; working together with other computers, it can access and
share the information and resources of local Lisas, or of remote computers.
What is the Lisa?
Lisa represents over 200 person years and $50 million of development effort.
Its intellectual inspiration came from the Smalltalk language and operating
system developed at the Xerox Palo Alto Research Center. This system’s
pioneering use of graphics and a mouse to present the fundamental concepts
of overlapping pieces of paper on an electronic desktop marked a departure
in computer operating software. Taking the Smalltalk concepts, Apple spent
three years refining them, adding innovations, and reducing costs.
Hardware is based on the MC68000 microprocessor. This chip’s large,
uniform address space, 32-bit wide internal data paths, and powerful regular
instruction set give it a clear advantage over many of today’s
microprocessors. Since Lisa was intended to be the first member of a powerful,
long-lived family of computer systems, this microprocessor’s capability
to gracefully evolve into faster and more powerful versions through the
1980s was also important.
As standard equipment, Lisa has a 1M-byte main memory – fully parity
checked to ensure reliable operation. Designed to support up to 2M-byte
main memory, this system also has special memory management hardware to
support multiprocessing. Lisa uses a 5M-byte Winchester disk and two built-in
floppy disk drives. These floppies, storing over 860K bytes of information,
are specially designed and developed to provide large capacity, reliability,
and foolproof operation. An IBM-like layout and numeric keypad are included
on Lisa’s detachable keyboard.
The most interesting feature of the hardware is the mouse –
a comfortable, convenient pointing device. Lisa’s mouse contains a
single button in order to eliminate user confusion. Also included is
a built-in 12” black and white bit-mapped display. This high resolution
device allows users to simultaneously display graphics symbols, multiple
fonts, and type styles on the screen.
The user interface is modeled around a desktop (see Fig 1) and contains
graphical images of familiar office objects such as documents, folders, and
stationery. Users control the machine by pointing at these images with
the mouse. Graphics and multiple type styles, up to one-third of an
inch tall, appear on the screen. These are reproduced with unparalleled quality
on the printed page. A companion dot matrix printer produces high resolution
text and graphics.
|Fig 1. The Lisa user interface takes the form of a littered desktop. Windows on various foreground and background tasks can be manipulated at will, and icons pointed to for the initiation of system functions. This visual/symbolic implementation avoids the constraints associated with command languages and mode based operations.|
Standard with the Lisa system are six integrated, consistent software
applications: a word processor; an electronic spreadsheet; a program that turns
numbers into meaningful business charts and graphs; a graphics editor to create
diagrams, drawings, and illustrations; a project scheduling program; and a database
program. Also available is a seventh application – an asynchronous communication
package emulating TTY, VT52, and VT100 terminals. IBM hosts can be accessed
through a 3270 communications package and 3270 cluster controller.
Existing solutions are inadequate
Although a wide variety of microcomputers are currently available, many do
not satisfy the needs of the typical information user. A major deficiency
in current microcomputers is the lack of suitable software.
Software consists of the operating system and applications that it supports.
Currently, such popular microcomputer operating systems as CP/M, MS-DOS, Apple
DOS, UCSD p-System, and Unix are fundamentally alike. Certainly, they differ in
the way to use the system, but the basic manner in which users interact with
the system is qualitatively similar. In reality, the computer industry is
developing the same operating system over and over.
Thus, it is not surprising that traditional operating systems do not meet
the needs of modern users since computer experts (ie. programmers) designed them
all for other computer experts’ use. Such expert users are comfortable
with the artificial concepts and terms upon which these operating systems
are built. They know, for instance, what a program is and what it means to
execute such a program. They understand the concept of a file, a directory
or catalog, and a disk volume. Most important, such experts are obviously
accustomed and willing to spend many hours studying the cryptic manuals required
to master such a technical subject. Soon, people like this will represent
a minority of microcomputer users. The Lisa user interface offers a welcome alternative.
The Lisa user interface
Consider the user interface of an operating system. This is the executive portion
that the users see when they first turn on the machine. Through this interface
a user controls the system, runs the programs, and manipulates data files. On
a traditional operating system, the system executive is a command interpreter.
The command interpreter interacts with the user through a predefined command
language similar to conventional programming languages. It is a rigid,
somewhat cryptic, and artificial syntax for the commands that the interpreter will
legally accept. For example, examine the commands used in several popular
operating systems to delete the file containing a Computer Design article:
|Apple DOS||DELETE Computer Design Article,S6,D2|
|UCSD p-System||F R Pubs:CmptrDesgn.Text|
Compare these traditional operating system commands with the Lisa user interface.
Here, a document icon is simply dropped into the Wastebasket Icon. While both
methods perform essentially the same function, the command syntaxes are certainly
not intuitive or easy to remember. If the actual command is ERA, it then does no
good to try KILL, DELETE, REMOVE, or even ERASE. Also, commands will not
work if B-, B–, or B/ instead of the B= are used in the file name. And, of
course, every data object in the system must have a unique file name to be
used when it is accessed. Because file names must be abbreviated to fit within
the maximum file name length allowed by each system, they tend to be very cryptic.
Lisa allows the name of a document to be almost any length or form. Names need
not even be unique.
Why use a command language to communicate with traditional operating systems?
Because programmers have a lot of experience with such languages and get
plenty of practice in using them. Knowing how to precisely specify syntax and
knowing certain programming techniques allow them to implement languages quickly
and efficiently. Therefore, the choice of a command language interface for
operating systems is largely for the convenience of the designer and
implementer of that system. Such a command language interface is certainly
not selected for the convenience of a user who is not a computer expert.
An unfortunate side effect of a command language interface is the heavy use
of modes that restrict system functions. For example, most text editors
have an insert mode that allows typed text to be inserted into the file.
Modes are objectionable for many reasons. The biggest reason, however,
is the myriad details that users must remember. These include how to get
into and out of a mode, what commands are and are not available, and most
importantly, what mode they are currently in.
It is probably impossible to design a serious system that has no modes
whatsoever. However, too many modes gives a user a feeling of constantly
navigating a command maze. This may be fun in a game like Adventure, but it
is frustrating and tiresome in the everyday use of an operating system.
Heavy use of modes also produces an inconsistent user interface. Commands and
capabilities in one mode are not usually available in another. In most systems,
for example, the commands for editing text entered into a text editor
are not available for editing the text entered to a file name request. Worse
still, the same command may not even have the same meaning in every mode. For
example, in one system, the command R is used to Run a program, Remove a file,
Replace selected text, or even to insert the letter R into a text file. Conversely,
two completely different commands may actually invoke similar or even identical
functions; for example, lines are deleted, but files are erased.
Compounding this problem of inconsistency in the user interface are
the application programs used with an operating system. Because application programs
are designed and sold separately from the system itself, more differences exist
between such programs and the operating system than between various parts of
the system. This is particularly true of portable application programs. Clearly,
such programs, designed to operate with a number of different operating
systems, will not be particularly consistent with any of them. It is practically
impossible to expect one conventional application to provide commands that
invoke functions similar with another.
Operating system calls
Although it is Lisa’s user interface that one first notices, the
fundamental system calls of the operating system are what make the
software revolutionary. Lisa’s operating system, designed specifically
as a single-user system, does not need the excess capabilities built into
multi-user, timesharing operating systems.
The operating system kernel provides multitasking support to the multiple,
simultaneous windows displayed on the Lisa screen and the switching among
them. In fact, an independent Lisa task is associated with each window.
Lisa’s multitasking is also used to allow such concurrent operations
as foreground user interaction and background printing. Sophisticated memory
management allows these multiple tasks to efficiently use and share system memory.
Specially designed to provide reliable storage of information, the Lisa
File System redundantly distributes and stores critical file system data such
as file directories. In the event of damage to the storage media, an
operating system Scavenger can repair damaged data and recover the user’s
information. The file system provides device independent access to information
through a byte-stream input/output interface.
Lisa’s operating system has additional capabilities that distinguish it from
traditional systems. Graphics and the desktop model are not just simply an
appendage to the operating system. Management capabilities of the graphics
screen are an integral part of the operating system design. The Window Manager
is responsible for keeping track of the number of open windows, the location
of each on the screen, the size of each, and which windows are in front of or
behind the other windows. For each window covered by other windows, and therefore
partially obscured, this Window Manager calculates that portion currently
visible. QuickDraw, a high speed, bit-map graphics package, automatically restricts
or clips any output to just that portion of the visible display window. When
windows are moved, resized, or otherwise changed, Window Manager redisplays
uncovered portions of windows. As a result, application designers need not
worry about where on the screen windows are located, or how much is currently
Similarly, mouse and keyboard support are an integral part of the operating
system. Hardware interface software responds to interrupts from such input
devices as the mouse or keyboard and queues input event information so that it
is not lost if the application is busy. The Event Manager classifies these events
and routes them to the proper window.
One of the most important aspects of Lisa is its printing technology. Superb
drawings, calculations, or reports on a computer are insufficient if one
cannot then print this information for others. Lisa supports both dot-matrix
and daisy wheel printers. The guiding philosophy behind Lisa’s advanced
printing technology is, what you see on the screen is exactly what you will
get on the printed page. This even extends to printing good quality graphics,
as well as the usual text, on a daisy wheel printer.
Closely associated with the Lisa Operating System is a library of software
modules (Fig 2). These modules perform various functions frequently
needed by the Lisa application programs. The use of library modules saves
an application designer the time it would take to develop similar
modules; it saves space on the disk; space in memory; and, most importantly,
guarantees consistency among the applications. There are modules to display and
select from pulldown menus, to allow viewing of different portions of a
document via scroll bars, to display alert messages informing the user of
errors, to enter and edit single lines of text, to perform floating point
computations, and to access database information.
|Fig 2. An integrated package of software supports all Lisa functions. The operating system kernel draws upon applications through system calls to the software library.|
The level of capability and power provided by Lisa’s operating system
and its library of software modules goes far beyond any traditional system.
But, providing additional capability allows the Lisa system to present the
user with a degree of simplicity never seen before in traditional operating
systems. The high degree of integration between hardware and operating
system software makes these advances possible.