You are here Home Windows Discussion Paper

64-bit Windows-7 Q & A

This paper discusses the pros & cons of using the 64-bit version of Microsoft's Windows 7 operating system on a desktop PC. A pdf version of the paper is available here. Please feel free to use it within your organisation.

Memory Addressing

In a 32-bit operating system, memory addresses are 32 bits in length, limiting the total number of unique addresses available to around 4 billion - effectively capping the total amount of memory your system can use at one time to 4GB.

A PC with a 32-bit version of Windows, is in fact limited to about 3.5 GB or less, the PC architecture reserves certain memory addresses. (I.E. even if a PC comes with 4 GB or more of memory installed, a 32-bit version of Windows can only use about 3.5 GB of that memory).

With 64-bit addresses, an operating system could theoretically use up to 16.8 million terabytes of RAM. Microsoft impose an upper maximum limit of 192GB of RAM in Windows 7 64-bit. All editions of Windows 7 (except for Home Basic) include both 32-bit and 64-bit software.

32-bit versus 64-bit processors

To run Windows 7 64-bit you must have a computer with a 64-bit processor (also called an x64 processor, or CPU).

Computers with a 64-bit processor can run either a 32-bit or 64-bit version of Windows.

You need at least 4GB of memory

A 64-bit operating system won't help if you don't have at least 4GB of memory. It will help a little bit if you have exactly 4GB, as 32-bit Windows actually limits you to using 3.5 GB, but it is unlikely to be noticeable.

32-bit drivers don't work

Generally, 32-bit applications work in 64-bit Windows, but the same isn't true for drivers. You will need a Windows 7 64-bit driver for each of your printers and scanners. This can be problematic if your peripheral hardware is old.

Some software breaks in 64-bit Windows

It's less common than hardware issues, but some programs break in 64-bit Windows. Particularly, old programs written for pre-XP versions of Windows may not work in 64-bit Windows 7.

If you're running a 16-bit program for some reason, it definitely won't work in a 64-bit operating system.

Also, even if a program has a 64-bit version, don't assume that all plug-ins for that program are 64-bit compatible as well. Not all Photoshop plugins, for example, will work in 64-bit Photoshop.

Not all software benefits from 64-bit

Finally, consider that when you upgrade to a 64-bit operating system, all your programs won't start taking advantage of the extra memory. A program has to be written and optimized with 64-bit processors in mind.

Internet Explorer

Internet Explorer is basically the combination of a number of platform components, including the networking components (URLMon/WinINET), the rendering components (MSHTML), the script engines (JScript.dll, vbscript.dll) and a variety of other components.

These components must be made available in 64-bit versions so that 64-bit applications can be built using these components. Additionally, because Internet Explorer can be launched/created/used as a COM Server, a 64-bit version must be available to enable hosting inside 64-bit processes.

Microsoft include the 32-bit version of Internet Explorer in the 64-bit version of Windows. The 32-bit version is always the default and that setting cannot be changed. The 32-bit version is more performant, but also the majority of plugins are built as 32-bit components.

Microsoft Office

By default, Microsoft Office 2010 installs the 32-bit version of Office 2010 even if the computer is running a 64-bit editions of Windows.

The 32-bit version of Office 2010 is the recommended option for most people, because it prevents potential compatibility issues with other 32-bit applications, specifically third-party add-ins that are available only for 32-bit operating systems.

Office 2010 provides support for the 32-bit version of Office 2010 programs running on 64-bit operating systems by using WOW64, a compatibility environment provided by the operating system that allows a 32-bit application to run on a Windows 64-bit operating system. Using the 32-bit version of Office 2010 allows people to continue to use existing third-party add-ins for Office that are 32-bit.

  • The ActiveX controls library, ComCtl, is not included in the 64-bit edition of Office. This library contains ActiveX controls that are used to build solutions. It is most commonly used in Access, Excel, and Word.

  • SharePoint List control is not included in the 64-bit edition of Office. The list view in SharePoint Technology is not available when using the 64-bit version of Office.

Compatibility with existing Office files and solutions

  • The 64-bit version of Office 2010 is not compatible with any other 32-bit version of Office programs.

  • Any solutions that use the ActiveX controls library, ComCtl will not work. No good alternatives are available for some of these controls.

  • There is no 64-bit version of Visual Basic 6. As a result, objects may need to be ported and rewritten.

  • Any Microsoft Visual Basic for Applications (VBA) script that contains the Declare statement will only work in the 64-bit version of Office if the code is updated manually.

  • The .MDE and .ACCDE files, a common way for Access application developers to distribute solutions, do not work in the 64-bit version of Office.

  • If the 64-bit version of Office is installed, certain Microsoft Office Communicator features that involve integration with Outlook are lost. For example, you cannot right-click a Communicator contact to schedule a meeting or send an e-mail message. This is because Office Communicator R2 is 32-bit, and Messaging Application Programming Interface (MAPI) calls do not cross the 32-/64-bit boundary.

Excel Compatibility

Generally workbooks are interchangeable between 32-bit and 64-bit editions of Excel. There's no special flag in the file marking it as a 64-bit workbook. Every day, smaller-sized workbooks will work OK in both environments. However, with 64-bit Excel it is possible to create workbooks that are too big for 32-bit Excel to open.

VBA code may require a review and updates in order for it to work with 64-bit Excel. Any ActiveX controls, COM Add-ins, or XLLs will also need to have 64-bit versions. The big advantage is the ability to create very large workbooks and pivot table caches.


A larger memory map can have huge performance advantages even if 32-bit applications are being hosted in the 64-bit environment. Reduced or no memory paging to disk can be achieved with sufficient memory making switching between applications instant.

Back to the top

Please contact us at
or by phone at +44 (0) 7771 784 246 or use our feedback form here.