Big changes

In almost every Windows OS release so far, we've changed something major in the OS subsystems, to improve the Windows infrastructure. And that generally screws up application or driver compatibility:

Windows 95

Long file names - Application developers had to fix their applications to support long file names. (A good thing, though: What is in 1NTINPRS.AVI?)

Windows NT

Driver developers had to write drivers for a new driver framework because of the hardware abstraction layer. Actually, most of them just stayed away, and supported Win9x only.

Windows 2000

A major annoyance for driver developers, who could ignore the NT driver models up to this point. Win2k ran on NTFS, and had locked-down permissions - developers couldn't install their application's files in \windows\system anymore.

We were telling corporations to set up their users as non-admins on their machines, and for the first time, corporate users in were logging in without admin rights, breaking all sorts of enterprise apps.

Consumers just sailed past, on to:

Windows XP

Installed on NTFS on default - breaking lots of applications that were used to the wide-open, unsecured world of FAT32.

We were telling the dads (or moms) of the world to run as administrator, and set up non-administrator accounts for everybody else in the household. Pretty much nobody did that - they all just logged on as Administrator. A situation that almost every bit of spyware exploited.

Which brings us to the OS everybody loves to hate (that isn't actually that bad) - the fustercluck known as:

Windows Vista

This time round, punch-drunk from all our security issues, the Windows team said: Fuck it, let's just lock it all down:

AUC: All your applications will run as non-administrator, even if you have an administrator account. No excuses. We've been telling you that you should do this since 1999.

A new graphics driver infrastructure: We had to protect the system from video driver crashes, as graphics card companies care only about performance, not stability.

Session 0 Isolation: No system service can directly create a UI. Lots of drivers and antivirus apps broke, but we fixed up a major security design flaw in Windows.

At this point, I can't think of any subsystem in Windows that needs a major change. *

Of course, with every new Windows release, subsystems are tuned up and cleaned up, but as far as I can see, it does not seem like there is a major bit of architecture that we need to change radically (as far as you application and driver developers are concerned). 

And that would be a good thing - your applications and drivers should then hopefully just keep on working in Windows 7. (And it does seem that we got bit in the ass a bit too hard with all the Vista appcompat issues.)

*as far as I can see. Who knows, a SuperUAC might be in the works. They might remove all security feature from the OS. They might make the UAC prompt pop up every five minutes. They might require driver writers to rewrite their drivers in Cobol.