SQL Server 2005 is supported on following three platforms
* X 86 platforms (32 bit)
* X 64 (X86-64) platforms (64 bit)
* And Itanium platforms (64 bit)
X86 and X64 chips are with same architecture while Itanium uses a different architecture.
X86 can access physical memory up to 64 GB using PAE and AWE and 4 GB of virtual memory. Intel and AMD have introduced processors that support both X86 and X64 architectures on same machine.
X64 can access up to 1-4 terabyte of physical memory and 256 terabyte of virtual memory. X64 is flexible platform, can work as 32-bit or 64-bit depending upon what operating system is installed. If 64-bit OS is installed even then 32-bit applications run. For SQL Server 2005, it is recommended that 64-bit version of SQL Server 2005 should be used with 64-bit OS (Windows Server 2003).
Itanium architecture is also known as IA-64 architecture. It can address physical memory up to 1 petabyte with 50-bit physical addressing mode. Virtual memory up to 60 exabyte may be addressed in 64-bit addressing mode. Microsoft has also introduced versions of Windows XP, Windows 2000 and Windows 2003 for Itanium processors. So SQL Server 2005 64-bit may be used on Windows 2000 and Windows 2003 on Itanium. A version of SQL Server 2000 is also available for Itanium but only with server components.
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