When Windows 7 launches sometime after the start of 2010, the desktop OS will be Microsoft's most "modular" yet. Having never really been comfortable with the idea of a single, monolithic desktop OS offering, Microsoft has offered multiple desktop OSes in the marketplace ever since the days of Windows NT 3.1, with completely different code bases until they were unified in Windows 2000. Unification isn't necessarily a good thing, however; Windows Vista is a sprawling, complex OS.

A singular yet highly modular OS could give Microsoft the best of all possible worlds: OSes that can be highly customized for deployment but developed monolithically. One modular OS to rule them all, let's say.

Mary Jo Foley is wagering that one of the big changes coming with Windows 7 is that it might be "available in pieces." That is to say, Windows 7 could be a modular OS. I'll go further. Windows 7 will be a modular OS, and we can already see the clues in Windows Vista, because it, too, is a fledgling modular OS. What we're talking about and why it matters (= software subscriptions), follows...

A modular Windows 7 is a lock

The first reason Foley gives is that Windows Server 2008 has "server roles" which can automagically determine which packages are installed and how the system in configured (more here). Foley suggests that this approach on the server side would translate well to the client, but the process of modularization has already begun on the client side.

Windows Vista was designed so that all three consumer editions—Basic, Premium, and Ultimate—can be installed off of one DVD and can be upgraded in place from one version to another. The changes can be "deep," since (for instance) Home to Premium can enable Aero Glass, and Premium to Ultimate can add BitLocker drive encryption, etc. My point is that Microsoft is already selling a "modular" OS, and the modules currently map to Windows Vista SKUs. Microsoft is also developing other modules around its Live efforts.

Unsurprisingly, Microsoft already has a patent on a "modular operating system" concept. A "core function" module, which includes the kernel, features a "license validation module" that authorizes the use of all additional modules, and uses DRM-like technology to prevent the use of unauthorized modules. Windows Vista uses part of its anti-piracy arsenal to validate and monitor changes to the OS for this reason.

So, Windows 7 will be modular, but to an unknown degree. I personally expect the modularization to focus on value-adds, as did Anytime Upgrade on Vista. It allows Microsoft to draw lines between what is and isn't "in" the OS for DoJ compliance issues. Whether it be Live Services, Windows Media Player, or even Internet Explorer, Microsoft could roll those into modules and then say, "Hey, look, that's not part of Windows, we're charging extra for that!" Foley says that she's heard from sources that Microsoft is working on a Photo + Mail + Video module that would exist apart from the OS, for instance. I've heard less specific groupings myself.

A brave, modular world (might not be so great)

Is a modular world a better one? For those of us having to manage software rollouts to scores of desktops, this would be yet another tool in the toolbox. Microsoft could create "desktop roles" like "information kiosk" that includes a stripped-down feature set, for instance.

Microsoft can also add/remove functionality module by module. New modules could be sold post-launch, keeping revenue streams strong. In fact, modules could be maintained independent of OS versions. Microsoft could create a "Live Services" module that is maintained by a dedicated team, designed to work across multiple OSes, yet provide a completely consistent experience.

A modular approach could also allow the company to make functionality available on a time-limited basis, potentially allowing users to "rent" a feature if it's needed on a one-off basis. Note that Microsoft is already testing "pay as you go" consumer subscriptions in developing countries.

The software+services side of modularization is what is surely driving this change at Microsoft. As I argued last summer, this is all a critical piece of Microsoft's software subscription dreams. In "2010, a 'Windows 7' software subscription odyssey," I noted that Microsoft has been reinventing its approach to Windows in order to facilitate the continued sales of multiple levels of the Windows "experience." Microsoft has confirmed that there will be multiple SKUs for Windows 7 and that there will be different subscription services built around the OS.

Whether or not this is a good thing is difficult to predict. Generally, we're very much in favor of package-based setup routines, much like you find with popular Linux distributions. Why run a web server when you don't need it? Why start device drivers that aren't going to be used? Why install a library on a system that doesn't need it?

But just imagine a Windows 7 install that allowed you to install only what you wanted. Don't like Internet Explorer, Windows Media Player, Windows Mail, Windows Firewall, etc.,? Don't install them or their supporting code. You've got to like that, if you're a Windows user.

Does this mean that Microsoft will ask you to subscribe to the next version of Windows, as opposed to buying it? That's unlikely, unless you're in business. The next consumer release will likely be a standalone OS stocked with an array of built-in and subscription-only modules.