There is a wonderful short story by Jorge Luis Borges ("Pierre Menard, Author of the Quixote") that, I believe, captures the open source effort to come to terms with Windows – which in some quarters is viewed as the antithesis of the philosophy of open source. In this short story, a critic analyzes Don Quixote as written by someone four hundred years later – someone who has attempted to live his life so as to be able to write the exact same words as in the original Don Quixote. The critic’s point is that even though the author is using the same words, today they mean something completely different.
In much the same way, open source has attempted to mimic Windows on “Unix-like” environments (various flavors of Unix and Linux) without triggering Microsoft’s protection of its prize operating system. To do this, they have set up efforts such as Wine and ReactOS (to provide the APIs of Windows from Win2K onwards) and Mono (to provide the .NET APIs). These efforts attempt to support the same APIs as Microsoft’s, but with no knowledge of how Microsoft created them. This is not really reverse engineering, as the aim of reverse engineering is usually to figure out how functionality was achieved. These efforts don’t care how the functionality was achieved – they just want to provide the same collection of words (the APIs and functionality).
But while the APIs are the same, the meaning of the effort has changed in the twenty-odd years since people began asking how to make moving programs from Wintel to another platform (and vice versa) as easy as possible. Then, every platform had difficulties with porting, migration, and source or binary compatibility. Now, Wintel and the mainframe, among the primary installed bases, are the platforms that are most difficult to move to or from. Moreover, the Web, or any network, as a distinct platform did not exist; today, the Web is increasingly a place in which every app and most middleware must find a way to run. So imitating Windows is no longer so much about moving Windows applications to cheaper or better platforms; it is about reducing the main remaining barrier to being able to move any app or software from any platform to any other, and into “clouds” that may hide the underlying hardware, but will still suffer when apps are platform-specific.
Now, “moving” apps and “easy” are very vague terms. My own hierarchy of ease of movement from place to place begins with real-time portability. That is, a “virtual machine” on any platform can run the app, without significant effects on app performance, robustness, and usability (i.e., the user interface allows you to do the same things). Real-time portability means the best performance for the app via load balancing and dynamic repartitioning. Java apps are pretty much there today. However, apps in other programming languages are not so lucky, nor are legacy apps.
The next step down from real-time portability is binary compatibility. The app may not work very well when moved in real time from one platform to another, but it will work, without needing changes or recompilation. That’s why forward and backward compatibility matter: they allow the same app to work on earlier or later versions of a platform. As time goes on, binary compatibility gets closer and closer to real-time portability, as platforms adapt to be able to handle similar workloads. Windows Server may not scale as well as the mainframe, but they both can handle the large majority of Unix-like workloads. It is surprising how few platforms have full binary compatibility with all the other platforms; it isn’t just Windows to the mainframe but also compatibility between different versions of Unix and Linux. So we are a ways away from binary compatibility, as well.
The next step down is source-code compatibility. This means that in order to run on another platform, you can use the same source code, but it must be recompiled. In other words, source-code but not binary compatibility seems to rule out real-time movement of apps between platforms. However, it does allow applications to generate a version for each platform, and then interoperate/load balance between those versions; so we can crudely approximate real-time portability in the real world. Now we are talking about a large proportion of apps on Unix-like environments (although not all), but Windows and mainframe apps are typically not source-code compatible with the other two environments. Still, this explains why users can move Linux apps onto the mainframe with relative ease.
There’s yet another step down: partial compatibility. This seems to come in two flavors: higher-level compatibility (that is, source-code compatibility if the app is written to a higher-level middleware interface such as .NET) and “80-20” compatibility (that is, 80% of apps are source-code incompatible in only a few, easily modified places; the other 20% are the nasty problems). Together, these two cases comprise a large proportion of all apps; and it may be comforting to think that legacy apps will sunset themselves so that eventually higher-level compatibility will become de facto source-code compatibility. However, the remaining cases include many important Windows apps and most mission- and business-critical mainframe apps. To most large enterprises, partial compatibility is not an answer. And so we come to the final step down: pure incompatibility, only cured by a massive portation/rewrite effort that has become much easier but is still not feasible for most such legacy apps.
Why does all this matter? Because we are closer to Nirvana than we realize. If we can imitate enough of Windows on Linux, we can move most Windows apps to scale-up servers when needed (Unix/Linux or mainframe). So we will have achieved source-code compatibility from Windows to Linux, Java real-time portability from Linux to Windows, source-code compatibility for most Windows apps from Windows to Linux on the mainframe, and Linux source-code compatibility and Java real-time portability from Linux to the mainframe and back. It would be nice to have portability from z/OS apps to Linux and Windows platforms; but neither large enterprises nor cloud vendors really need this – the mainframe has that strong a TCO/ROI and energy-savings story for large-scale and numerous (say, more than 20 apps) situations.
So, in an irony that Borges might appreciate, open-source efforts may indeed allow lower costs and greater openness for Windows apps; but not because open source free software will crowd out Windows. Rather, a decent approximation of cross-platform portability with lower per-app costs will be achieved because these efforts allow users to leverage Windows apps on other platforms, where the old proprietary vendors could never figure out how to do it. The meaning of the effort may be different than it would have been 15 years ago; but the result will be far more valuable. Or, as Borges’ critic might say, the new meaning speaks far more to people today than the old. Sometimes, Don Quixote tilting at windmills is a useful thing.