Microsoft's announcement that Exchange Server 2007 will be a native 64-bit application requiring a 64-bit OS and hardware platform is part of a growing 64-bit migration. For SQL Server customers this migration might seem like a huge change. Before SQL Server 2005, only the significantly more expensive Itanium-based systems supported 64-bit. However, the widespread adoption of the newer 64-bit x64 architecture and Microsoft's native x64 versions of Windows Server 2003 and SQL Server 2005 Enterprise and Standard Editions has paved the way for moving to 64-bit SQL Server. I'd like to point out the most significant benefits you'll get by running SQL Server 2005 on the 64-bit x64 platform.
1. Increased RAM Support
RAM is one of the most important performance components for a relational database server, but 32-bit systems can natively address only up to 4GB of RAM, 2GB of which is reserved for the OS. This limitation leaves 2GB for applications such as SQL Server. By using Address Windowing Extensions (AWE), a 32-bit system can address up to 64GB of RAM. However,AWE imposes overhead for address virtualization on 32-bit systems; plus, only the SQL Server buffer cache can use the additional RAM that AWE makes available. In contrast, the x64 processor can address up to 1TB of RAM (although the largest x64 systems to date support a maximum 128GB of RAM). Both the OS and SQL Server can use this RAM, and it's not limited to the buffer cache. Increased memory capability results in better performance in many cases because it reduces the need for disk I/O.
2. Improved I/O Performance
Although the vastly increased memory ceiling helps reduce I/O, I/O is still a necessity. The 64-bit x64 architecture effectively doubles the available data path, improving system throughput. And newer systems provide radically improved bus technologies such as AMD's HyperTransport bus, which is capable of internal data transfers at a rate of 8GB per second.
3. Running 32-Bit Applications at Full Speed
Unlike the Itanium platform, the x64 platform can run 32-bit applications at full speed side-by-side with native 64-bit applications, without Itanium's 32-bit emulation overhead. Windows Server 2003 x64 runs 32-bit applications by using the built-in Windows on Windows64 subsystem. Note that SQL Server client tools don't require 32-bit support because they're native 64-bit applications.
4. Identical On-Disk Structures
In 1998, Microsoft redesigned SQL Server 7.0 with the goal of running on 64-bit systems, and all of the SQL Server on-disk structures from that version forward are 64-bit-compatible. Database migration to a 64-bit server system is as simple as detaching the databases from the 32-bit server and attaching them to the 64-bit server.