I recently had to purchase some new machines to run some Operations Research software. The type of software we're running needs a strong CPU but not too much RAM; We're okay with 4GB. All the new high-end CPUs are 64-bit. Unfortunately, the IDE for the software we're going to be running only supports 32-Bit OSs. I talked to the company that makes the software, and they recommended I go ahead and purchase the 64-bit machines.
They suggested we run a 32-bit OS on them until the next release of the IDE. It will be 64-bit-compatible and will come out in the Spring. While we're using the 32-bit OS, we'll be limited to 4GB of RAM, and we won't be even be able to access it all. I think we'll be able to use around 3/4 of the total amount. I also noticed this degradation with my 64-bit AMD processor I've been using at home for the last couple of years. It's basically because some RAM will need to be reserved by things like the PCI bus and video cards, but if you want a more detailed explanation, check out IanG's article on the subject. However, since we're going to take a chance and go with Vista, we'll be able to re-gain some of the paging latency by using ReadyBoost.
Unfortunately, this isn't the first time I've encountered problems with software that doesn't support 64-bit OSs. The good news is that we may be at the end of one of those awkward periods when hardware evolves and software lags behind. We're at the point when it generally
makes sense to buy 64-bit machines and run 32-bit OSs in case the software we need hasn't caught-up. It can't afford to wait much longer.