One of the bullet point features of Lightroom 2.0 is that it supports the latest 64-bit systems on both Windows and Intel-based Macs. For 64-bit Windows Vista, you have to use a separate download to get 64-bit support. On the Mac, all you need to do is uncheck a box. But once you're running in 64-bit mode, what does it really get you?

For starters, it lets Lightroom access more than 4GB of memory. This is the feature that most people focus on and it's a decent enough one. But it's not the whole story. You see, Intel's latest 64-bit capable chips, like the Intel Core 2 Duo in the MacBook Pro, has two modes. One is the 32-bit mode that is compatible with Intel instructions dating back to the dawn of 32-bit computing. Because Intel's 32-bit mode was defined so long ago, it's actually can't take full advantage of what the latest CPUs are capable of. This is all good and fine when you want compatibility, but it has been holding software a bit lately.

Because the whole notion of binary compatibility goes out the window when moving to 64-bit—programmers have to recode and recompile their software to take advantage of 64-bits—it gives everyone, application programmers, operating system providers, and hardware designers, an opportunity to jump past the historical limits of the 32-bit instruction set and gain a respectable performance increase in the process. Now, we're not talking double the performance by any means, but many of my software developer friends have noticed off the cuff gains of 5% to 15% when recompiling their Mac OS X applications to run in 64-bit mode.

It's too early to say what absolute effect running in 64-bit mode will have on Lightroom's performance, but given the task at hand, which often sees me moving through hundreds, sometimes thousands of RAW photos in the space of an hour or two, every last little bit helps. Even if we only see just a few percentage points improvement in the end, I'll take it.

Oh, and if you're on a Mac with an Intel 64-bit CPU (every Mac sold in the last year and probably the majority of Intel-based Macs ever sold fall into this category) and have the Lightroom 2 beta, you can enable 64-bit mode by going into the Finder and bringing up the Info box on the Lightroom 2 application. Uncheck the "Open in 32 Bit Mode" box and you're set.