DIFFERENCE BETWEEN X64 AND X86

x86 refers to any processor that is instruction-compatible with the Intel 8086 and higher. This includes the Pentium, Pentium II, Celeron, Pentium III, Pentium 4, Pentium D, Core Duo, Core 2 Duo, Core i7, Atom, AMD Athlon, Sempron, Athlon 64, Phenom, and Geode. In summary 32 bit type processors

x64 is often used to refer to any x86 processor that has 64-bit extensions (x86-64). These include the AMD Athlon 64, late models of the Pentium 4, Pentium D, Core 2 Duo, Phenom, and certain Geode processors. In summary 64 bit type processors


x32 is a retcon of the x64 term to apply to either 32-bit only processors or programs.

Microsoft publishes KB946765 which details the main differences between 32-bit and 64-bit Windows Vista, which mainly relate to memory accessibility, memory management, and enhanced security features, as listed in table below.

Architecture	Windows Vista, 32-bit versions	Windows Vista, 64-bit versions
System requirements	1-gigahertz (GHz) 32-bit (x86) processor or 64-bit (x64) processor, 512 MB of RAM	1-GHz 64-bit (x64) processor, 1 GB of RAM (4 GB recommended)
Memory access	A 32-bit version of Windows Vista can access up to 4 GB of RAM.	A 64-bit version of Windows Vista can access from 1 GB of RAM to more than 128 GB of RAM.
Memory access per edition	All 32-bit versions of Windows Vista can access up to 4 GB of RAM.	Windows Vista Home Basic – 8 GB of RAM Windows Vista Home Premium – 16 GB of RAM Windows Vista Business – 128 GB of RAM or more Windows Vista Enterprise – 128 GB of RAM or more Windows Vista Ultimate – 128 GB of RAM or more
DEP	32-bit versions of Windows Vista use a software-based version of DEP.	64-bit versions of Windows Vista support hardware-backed DEP.
Kernel Patch Protection (PatchGuard)	This feature is not available in 32-bit versions of Windows Vista.	This feature is available in 64-bit versions of Windows Vista. Kernel Patch Protection helps prevent a malicious program from updating the Windows Vista kernel. This feature works by helping to prevent a kernel-mode driver from extending or replacing other kernel services. Also, this feature helps prevent third-party programs from updating (patching) any part of the kernel.
Driver signing	Unsigned drivers may be used with 32-bit versions of Windows Vista.	64-bit versions of Windows Vista require that all device drivers be digitally signed by the developer.
32-bit driver support	32-bit versions of Windows Vista support 32-bit drivers that are designed for Windows Vista.	64-bit versions of Windows Vista do not support 32-bit device drivers.
16-bit program support	32-bit versions of Windows Vista support 16-bit programs, in part.	64-bit versions of Windows Vista do not support 16-bit programs.