I was kind of suprised when I saw this blog post. Saying that 64-bit processing wasn’t allowed with Standard Edition of BizTalk. Since I was at PDC at the time I asked the team who were (without me putting words in their mouths) equally suprised. At the time they couldn’t see either a licensing or technical reason as to why that would be so. And to add to that it made little sense that Branch was allowed while Standard was not.
I didn’t have access to machines (or time) to test right then, but after getting back I tested and true enough you are not allowed to create a 32-bit host. The UI stops you. As you can see, this doesn’t stop BizTalk Server Standard from being installed on a 64-bit machine – it just doesn’t get the benefits of 64-bit processing.
I also found an “official” explanation to this here, which I’ve pasted below:
"We consider 64-bit support an Enterprise Edition level feature that a customer would only select if they require faster messaging/orchestration processing or the larger addressable virtual memory of 64-bit mode for large BizTalk message mapping or other memory intensive operations. Because the Standard Edition is designed for small-to-medium environments, it is licensed to only run on a single BizTalk server with a maximum of two CPUs, maximum of five "BizTalk Applications", and a single message box. 64-bit support for the Standard Edition seemed counter-intuitive from a technical and licensing perspective. If the deployment scenario requires 64-bit hardware then it certainly requires BizTalk Enterprise as well. Standard edition is for single box only installations. Enterprise is also required for multi box installs and for clustering."
Judging from the teams initial reaction and the fact that 64-bit is now very much mainstream, especially on servers, I would expect to see this change in the upcoming releases of BizTalk Server.