Yesterday, I reported on the availability of 8GB memory modules from OWC that allow up to 32GB memory in a quad-core Mac Pro, greatly extending its useful headroom, but I lamented the fact that 8-core machines apparently had a 32GB limit.
It turns out that this might not be true after all— apparently booting into the 64-bit Mac OS X Snow Leopard kernel allows all 64GB to be used!
I have been running continuously in 64-bit kernel mode for six weeks or so now on both my quad-core and 8-core Mac Pro. They are working flawlessly, and things are definitely perkier with the 64-bit kernel, especially photo applications. So if no hardware or its driver support precludes the switch to the 64-bit kernel, go ahead, it’s worth it. An eSATA card is one possible sticking point, but I use the FirmTek SeriTek 2ME4-E and it’s rock-solid.
Few users need 64GB, or even 32GB, but there are use cases for it, such as monster files in Photoshop. A future 64-bit Photoshop CS5 will be a Big Deal for users working with monster files, but lots of memory helps today with huge files even though Photoshop CS4 is a 32-bit application on Mac OS X, see Optimizing Photoshop — my groundbreaking research shows the benefits clearly.