This article describes the differences between the 32-bit versions of Windows Vista and the 64-bit versions of Windows Vista.

Note To use a 64-bit version of Windows Vista, you must have a computer that has a 64-bit processor. Also, you must have 64-bit device drivers for the devices that are in the computer.

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You may want to determine whether the platform of Windows Vista is installed. To verify that you have the platform of Windows Vista, follow these steps:

1.	Click Start, right-click Computer, and then click Properties.
2.	The operating system appears as follows: • For a 64-bit version operating system, "64-bit Operating System" appears for the system type under System. • For a 32-bit version operating system, "32-bit Operating System" appears for the system type under System.

Note Microsoft Win32 uses the x86 processor in 32-bit flat mode. Therefore, a x86-based version means a 32-bit version operating system.

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The main differences between the 32-bit versions of Windows Vista and the 64-bit versions of Windows Vista relate to memory accessibility, memory management, and enhanced security features. The security features that are available in the 64-bit versions of Windows Vista include the following:

•	Kernel Patch Protection
•	Support for hardware-backed Data Execution Protection (DEP)
•	Mandatory driver signing
•	Removal of support for 32-bit drivers
•	Removal of the 16-bit subsystem

One of the greatest advantages of using a 64-bit version of Windows Vista is the ability to access physical memory (RAM) that is above the 4-gigabyte (GB) range. This physical memory is not addressable by 32-bit versions of Windows Vista.

Depending on the version of Windows Vista that is installed, a 64-bit version of Windows Vista supports from 1 GB of RAM to more than 128 GB of RAM. The ability to address more physical memory lets Windows Vista minimize the time that is required to swap processes in and out of physical memory. Therefore, Windows Vista can manage processes more efficiently. This memory management feature helps improve the overall performance of Windows Vista.

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Advantages when you install a 64-bit version of Windows Vista

•	Increased memory support beyond that of the 4-GB addressable memory space that is available in a 32-bit operating system
•	Increased program performance for programs that are written to take advantage of a 64-bit operating system
•	Enhanced security features

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What to consider when you install a 64-bit version of Windows Vista

•	64-bit device drivers may not be available for one or more devices in the computer.
•	Device drivers must be digitally signed.
•	32-bit device drivers are not supported.
•	32-bit programs may not be fully compatible with a 64-bit operating system.
•	It may be difficult to locate programs that are written specifically for a 64-bit operating system.
•	Not all hardware devices may be compatible with a 64-bit version of Windows Vista.

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The main differences between the 32-bit versions of Windows Vista and the 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 - 4 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.

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For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base:
For more information about 64-bit versions of Windows Vista, visit the following Microsoft Web site:

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