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Microsoft Windows XP Professional x64 Edition released on April 25, 2005 by Microsoft is a variation of the Windows XP operating system for x86-64 personal computers.

Windows XP Professional x64 Edition uses version 5.2.3790.1830 of core files, the same version used by Windows XP 64-bit Edition 2003 and Windows Server 2003 SP1 as they were the latest versions during the operating system's development. It is designed to use the expanded 64-bit memory address space provided by the x86-64 architecture.

The primary benefit of moving to 64-bit is the increase in the maximum allocatable system memory (RAM). Windows XP 32-bit is limited to a total of 4 GB, which is, by default, equally divided between Windows kernel and application usage. Using the /3GB switch in the boot.ini file forces Windows to limit the kernel to the upper 1GB and provides up to 3GB for applications. Windows XP x64 can support much more memory; although the theoretical memory limit a 64-bit computer can address is about 16 exbibytes (16 billion Gibabytes), Windows XP x64 is currently limited to 128 GB of physical memory and 16 TiB of virtual memory. Microsoft claims this limit will be increased as hardware capabilities improve.

Windows XP Professional x64 Edition is not to be confused with Windows XP 64-bit Edition, as the latter was designed for Intel Itanium processors, although they both are commonly referred to as '64-bit Windows' by Microsoft due to their similarities from developer's point of view.

Both Windows Server 2003 x64 and XP x64 use identical kernels and code base. This is evident when the System Information tool reports the current OS as Windows Server 2003 x64 and not Windows XP.

Service Pack 2 (SP2) was released on the 12th of March 2007. This service pack is not equivalent to Service Pack 2 for 32-bit versions of Windows XP. In fact, due to the earlier release date of the 32-bit version, many of the key features introduced by Service Pack 2 for 32-bit (x86) editions of Windows XP were already present in the RTM version of its 64-bit (x86-64) counterpart.