It seems we have some badly worded docs on some Microsoft sites that may lead you to believe that you cannot run Exchange 2003 on x64 bit systems. Also the release notes seem to be in error as well...
Published Nov 18, 2005
Version 1.0
Blog Post
Bob Muglia’s Keynote address at the Microsoft IT Forum on November 15:
We are also focusing on the next version of Exchange next year, codenamed Exchange 12. That will also be 64-bit only. The reason we have chosen to do this with Exchange is because like database, messaging is an environment that can take advantage of all of the memory that 64-bit opens up. We found that Exchange 12 has tremendously different performance characteristics than Exchange 2003 because of the incremental memory that is available to 64-bit. We found that there is a 70% reduction in the IOs required for Exchange 12. That makes us a different beast in terms of the performance characteristics. Today’s Exchange systems typically require the highest performance SAN-based systems to provide the scalability that major organisations need. With Exchange 12 and the incremental memory, the IO throughput is dramatically reduced. You may choose to continue to run it on a SAN, but the kind of IO subsystems and throughput needed will be reduced dramatically with Exchange 12. As we move forward, based on Exchange 12, our new generation solutions such as Small Business Server and Central will also be 64-bit only. We are planning on shipping those in the 2007 timeframe.
We are also focusing on the next version of Exchange next year, codenamed Exchange 12. That will also be 64-bit only. The reason we have chosen to do this with Exchange is because like database, messaging is an environment that can take advantage of all of the memory that 64-bit opens up. We found that Exchange 12 has tremendously different performance characteristics than Exchange 2003 because of the incremental memory that is available to 64-bit. We found that there is a 70% reduction in the IOs required for Exchange 12. That makes us a different beast in terms of the performance characteristics. Today’s Exchange systems typically require the highest performance SAN-based systems to provide the scalability that major organisations need. With Exchange 12 and the incremental memory, the IO throughput is dramatically reduced. You may choose to continue to run it on a SAN, but the kind of IO subsystems and throughput needed will be reduced dramatically with Exchange 12. As we move forward, based on Exchange 12, our new generation solutions such as Small Business Server and Central will also be 64-bit only. We are planning on shipping those in the 2007 timeframe.