The 64-bit version of Exchange Server provides new opportunities for performance and scalability. Because of the incremental memory that is available with 64-bit, Exchange 2007 has tremendously different performance characteristics than Exchange Server 2003. 64-bit code also means a substantial reduction in the I/O required for Exchange 2007. Today’s larger Exchange deployments typically require a high-performance storage area network (SAN)-based storage solution to provide scalability. With Exchange 2007 and the incremental memory, the I/O throughput is dramatically reduced. You can continue to run Exchange 2007 on a SAN, but the necessary I/O subsystems and throughput are reduced dramatically with Exchange 2007.

The 64-bit architecture also provides a significant increase in the number of storage groups and databases that you can create on a single Exchange 2007 server. Earlier versions of Exchange Server were limited to a maximum of four storage groups and five databases in each storage group. Exchange 2007 increases the maximum number of storage groups and databases substantially. You can create a maximum of 50 storage groups on each Exchange 2007 server, with up to a maximum of 50 databases.

The 64-bit architecture means that existing Exchange Server 2003 servers cannot be upgraded in-place. Instead, new 64-bit capable hardware must be purchased so that new Exchange 2007 servers can be deployed.

Note:
While you can put more than one database in a storage group, we recommend that you only use one database per storage group for maximum availability.

The database engine and cache in Exchange 2007 has been optimized for scalability. These changes also mean that reduced I/O throughput is needed. Larger memory systems allows for a larger amount of cache to be allocated to the Exchange store, which allows for the allocation of more cache on a user-by-user basis, thereby increasing the probability that data requested by the client will be serviced out of memory instead of by the disk subsystem.

In addition, the database page size has been increased from 4 kilobytes (KB) to 8 KB. An 8 KB page size means a greater probability that the contents of an entire message will be read during a single I/O operation, and that the messages contents can now be stored on a single page in the database.

In Exchange 2007, the transport pipeline is a collection of server roles, connections, components, and queues that work together to route all messages to a categorizer on a Hub Transport server inside the organization. The new transport engine can support a significantly larger number of messages than earlier versions of Exchange.

For more information about the new transport pipeline in Exchange 2007, see New Transport and Routing Functionality.