Microsoft Exchange is a mission-critical, infrastructure staple in organizations of all sizes. As an application that demands high levels of the "-abilities" (availability, reliability, scalability, etc.) and stringent resource demands, the sizing process is critical to ensuring a healthy production environment. Sizing Exchange 2007, which introduces new roles and routing architecture, replication options, improved indexing and search capabilities, security and compliance capabilities, leveraging the latest x64 hardware, represents new challenges and opportunities over its predecessors. This talk first covers why the move to 64-bit was necessary, and how this move has impacted the sizing rules-of-thumb and approaches. Then covers key enabling hardware advancements, such as x64 architectures, multi-core processors, SATA and SAS disk technology, and how these technologies will play a key role moving forward with Exchange 2007. Finally, the talk provides rules-of-thumb, based jointly on HP characterization testing and HP / Microsoft best practices, for sizing the key server roles and technologies such as CCR and SCR associated with typical Exchange 2007 SP1 deployments.