A Messy Transition: Practical Problems With 32bit Addressing In Windows

Except in a few cases where 64-bit code is clearly faster, the primary purpose for Vista x64's existence is to resolve the problems of 32-bit addressing space, and we're just not at the point yet where even most enthusiasts are pushing that limit. Once applications begin to push the 2GB addressing space limitation of Win32 (something we expect to hit very soon with games) or total systems need more than 4GB of RAM, then Vista x64 in its current incarnation would be a good choice.

For some time now we have been mentioning the potential problems that are likely to result from the switchover from 32bit(x86) Windows to 64bit(x64) Windows. Due to a multitude of issues, including Windows' memory management, the basic design of the PC architecture, and consumer support issues, there is no easy path for mass migration from 32bit Windows to 64bit Windows. As a result we have been expecting problems as consumers begin to make the messy transition.

We published the above mentioned guide on February 1st, expecting the fall/winter 2007 games to be the ones to push the 2GB addressing space limitation of Windows, and it turns out we were wrong. It turns out that two weeks after we published the above article, THQ published Supreme Commander, a RTS with a massive appetite for resources. It can be simultaneously GPU limited and CPU limited, which is why it's a standard benchmark here for our performance articles, it's also memory limited in more than one way: it's hitting the 2GB barrier of 32bit Windows.

An artifact of the design of 32bit processors and the 32bit API for Windows, the 2GB barrier is a cap on how much addressing space (related to but not equivalent to memory usage) a single application can use. This isn't a bug but rather the result of how hardware and software was created so many years ago, and while everyone has known this barrier will inevitably be hit, as we'll see there are several reasons why it can't simply be moved or bypassed. Meanwhile hitting it involves affected applications crashing for what can appear to be no good reason, and understanding why the 2GB barrier exists and what can be done will be important for resolving those crashes.

On a personal note, I am a semi-casual player of real time strategy(RTS) games and I've been playing Supreme Commander lately. This is a different kind of article, it's a record and the result of my own efforts to resolve why I was having crashing issues with Supreme Commander. With no intended disrespect towards THQ or the game's developers (Gas Powered Games) we could have not possibly asked for a better example of the 2GB barrier in action. It's exactly the experience we believe many people will have as they hit the 2GB barrier, mainly those power users who use large monolithic applications such as games or multimedia tools. This is an article on what the problem with the 2GB barrier is, what kind of experiences a user may expect when hitting it, and what can be done to fix it.

But before we get too far ahead of ourselves, let's discuss memory management in Windows. Understanding the problem with Supreme Commander requires understanding what the 2GB barrier is, why it's there, and what makes it so problematic.