A description of the differences between 32-bit versions of Windows Vista and 64-bit versions of Windows Vista

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.