Java's three types of portability

Find out about the types of portability Java supports, and how Microsoft could undermine the technology by subverting the one type that most threatens its hold on the desktop operating system market

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  • Portable application software can allow users of non-Windows and non-Macintosh machines access to a lot of software otherwise unavailable. OS/2, an operating system that is generally considered quite good technically, suffers horribly from a lack of application software. OS/2 users would benefit tremendously from good Java applications.

  • Portable application software puts pressure on the OS vendors to provide better products and respond to customer feedback. Currently, once you choose an operating system, you're stuck -- switching would involve too much repurchasing of software (and the vendor knows this). Java applications make switching operating systems easier, forcing OS vendors to be more responsive to their customers because of the threat of defection.

  • Portable application software can give users more choices because software vendors who might have elected to support only one or a few operating systems now can support all operating systems with a Java implementation.

  • Portable application software can make life easier for users who must use several different types of machines. They will have the chance to use the same software on the various machines.

MIS departments: Software maintenance gets simpler

MIS departments see one very big benefit to Java portability: the reduction of the number of different pieces of software they must maintain. Consider a company with Windows machines, Macintoshes, and Unix machines -- not all that unusual these days. Such a company often needs a variety of software packages that perform the same task. To meet word processing needs, it might use both Microsoft Word for the Macintosh and Word for Windows (quite possibly different -- and incompatible -- versions). In fact, chances are, the company will have several versions of Word for Windows (to accommodate Windows 3.x and Windows 95/NT machines). Finally, except via a Windows or MacOS emulator, Word won't run in any flavor on a Unix machine, which makes it likely those users will have to use a different word processor. Passing files between these various systems can be difficult at best.

A single word processor running on all these machines would make life much simpler for the MIS department.

What portability really means to Microsoft

Java is an example of something Alvin Toffler calls a "product system." Just like highways and cars, and unlike umbrellas, product systems derive their benefits from the interaction of many things rather than the individual things themselves. He writes:

Umbrellas and automobiles are different... . A person can use an umbrella without buying another product. An automobile, by contrast, is useless without fuel, oil, repair services, spare parts, not to mention streets and roads.

The mighty auto ... is a team player completely dependent on other products. So is a razor blade, a tape recorder, a refrigerator, and thousands of other products that work only when combined with others...

Each of these is part of a product system. It is precisely their systemic nature that is their main source of economic value. And just as "team players" must play by certain agreed-on rules, systemic products need standards to work. A three-pronged electrical plug doesn't help much if all the wall sockets have only two slots.

The distinction between stand-alone and systemic products throws revealing light on an issue that is widening today's information wars all around the world. The French call it la guerre des normes -- "the war over standards." Battles over standards are raging in industries as diverse as medical technology, industrial pressure vessels, and cameras.

Some of the most explosive -- and public -- disputes are directly related to the ways in which data, information, knowledge, images, and entertainment are created and distributed.

-- from PowerShift, Chapter 12: "The Widening War," by Alvin Toffler

A J-code program is useless without a JVM to run it. Additionally, a JVM is useless without a J-code program to run. Even a single JVM and a single J-code program are fairly useless in isolation. The combination of many J-code programs and JVMs is what creates value.

There already is a war in progress over the direction Java is to take. Three major companies, Sun, Netscape, and Microsoft have differing views about the future of Java. Sun and Netscape see Java as a tool for creating applications and applets that run everywhere. Microsoft sees Java as a tool for creating applications that run on Windows.

Java as a language does not threaten Microsoft. As long as the Java language works with and on Microsoft operating systems, it is no more threat to Microsoft than other programming languages.

Java as a virtual machine is not much of a threat. Windows NT has implementations for Intel x86 machines, DEC Alpha machines, MIPS, and PowerPC machines. (However, support for MIPS and PowerPC ends with Windows NT 4.0.) Microsoft need not care about the difference between Windows programs that run on Intel machines and Windows programs that run on non-Intel machines.

The Java OS/GUI libraries do threaten Microsoft. The ability to easily switch operating systems is a threat to a company with 80 to 90 percent of the desktop operating system market. Even more dangerous to Microsoft is the possibility that if enough portable Java applications are written, need for Windows evaporates. The much simpler JavaOS will run all the Java applications without a Microsoft operating system. Thus, Java directly threatens Microsoft's operating systems business.

Microsoft can employ two tactics. The first is to implement standard Java libraries poorly or not at all, and then provide a Windows-only alternate library that runs well on Windows operating systems and not at all on non-Microsoft operating systems. The second tactic is to add functionality to the standard Java libraries by providing libraries to fill voids. For example, the Java Abstract Windowing Toolkit (AWT) does not provide access to all the Windows GUI functionality. Microsoft can extend the AWT to provide access to these functions. A side effect is that Java programs using these library extensions won't be portable to non-Windows machines.

We already see indications of Microsoft's intention to pursue both approaches. According to PCWeek, Microsoft "will not support all the core JDK 1.1 APIs in Internet Explorer or Windows." In addition, the magazine noted Microsoft "plans to create Java libraries dependent on Win32 APIs."

For some applications, this extra non-portable functionality will be useful enough to give up the portability to non-Microsoft operating systems. But for many other applications, using these extensions will add only cosmetic appeal with little functional benefit while locking the application and its users into the Microsoft universe.


Java provides three different types of portability, and the way the three interact is what makes Java special. Without CPU and OS/GUI portability, Java is just another good programming language. The Java language and the Java virtual machine without OS/GUI portability creates programs that port between, for example, different CPUs running Windows NT but not between machines running Windows and machines running MacOS. We don't need Java for this; we can do it today with a recompile. To achieve Sun's goal of "Write once, run anywhere," programs cannot sacrifice any of the three forms of portability provided by Java. It will be both easy and alluring, in the near future, to write "portable" Java programs that in reality port only between machines running Windows, and Microsoft can be expected to encourage this. Whether programmers and the companies they work for resist this while still writing programs that meet their users' needs remains to be seen.

Mark Roulo has been programming using C and C++ for the past seven years. He has been using Java for over a year and is implementing an ANS-compliant Forth interpreter in Java. His main programming interests are portable, distributed, concurrent software, as well as software engineering. Mark would like to thank his wife, Dara Golden, for wading through and editing the first three drafts of this article.

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