X64

What is X64?
x86-64 is an extension of the x86 instruction set. It supports vastly larger virtual and physical address spaces than are possible on x86, thereby allowing programmers to conveniently work with much larger data sets. x86-64 processors are commonly known as "64-bit" processors, and operating systems that take advantage of the 64-bit instruction set are known as 64-bit OS's.



History
The original x86-64 specification was created by AMD and first implemented in the AMD K8 family of processors. AMD named their technology AMD64. It was created as an alternative to Intel's IA-64 (Itanium) architecture, which was not compatible with the existing x86 architecture. Intel began to implement the x86-64 instruction set under several names, including IA-32e, EM64T, and currently, Intel 64.

Compatibility
Being an extension of the x86 instruction set, 64-bit processors utilizing the x86-64 architecture are fully compatible with i386 (32-bit) software, which simply will not be able to recognize the extended memory benefits of the 64-bit architecture. Most modern operating systems, including Windows, OS X, and most modern Unix-like operating systems are available in 64-bit editions.