Understanding 64-Bit Office

Microsoft Office 2010 marks the first time Office will be shipping in both 32-bit and 64-bit versions.

With Windows 7, you have the option of running 64-bit Windows on your 64-bit PC, and now with Office 2010 you have that same choice. As 64-bit processors and operating systems are becoming the standard for systems ranging from servers to desktop computers, 64-bit Office will be able to take advantage of everything that 64-bit systems have to offer.

Some users need greater memory capacity, and those who crunch huge Excel spreadsheets filled with financial data or those who track large projects (such as building an aircraft carrier) using Microsoft Project have that capability. File sizes greater than 2 GB are now possible for applications such as 64-bit Excel and Project, with pretty much all the same user experience and functionality as 32-bit Office. It’s important to note, however, that 32-bit and 64-bit Office side-by-side on the same machine is not supported.

In this post, I’ll help you decide what version is best for you, show you how to install the version you want, provide some background on 64-bit Office, and list some things you should keep in mind.

What does “64-bit” mean?

First, let’s take a step back and understand what 64-bit means. A 32-bit processor uses a 32-bit memory address length, which limits the memory it can address to about 4 GB. As users are running more memory-intensive applications at once, a 32-bit address length is no longer adequate. Enter the 64-bit processor, which can address a potential 17 billion GB.

With a 64-bit processor, you can install a 32-bit or a 64-bit operating system (OS), though only a 64-bit OS is capable of addressing more than 4 GB of memory. Finally, depending on what OS you’ve installed, you can then install a 32-bit or 64-bit application. There is support for 32-bit applications to run on 64-bit Windows using Windows-32-on-Windows-64 (WOW64).

Benefits of 64-bit Windows with 32-bit Office

Before talking about 64-bit Office, I want to emphasize how much better 32-bit Office is on 64-bit Windows compared to 32-bit Windows. The basic reason is simple.  On 32-bit Windows, it doesn’t make sense to install more than 4 GB of physical memory because anything beyond 4 GB can’t be addressed. However, the limitation means constantly jumping among multiple applications could degrade performance because of thrashing.

On 64-bit Windows, you can install a lot more physical memory.  While we work hard to minimize the amount of memory our applications use (Office 2010 has the same minimum memory requirements as Office 2007), this ability to access more memory means that 32-bit Office applications on 64-bit Windows will be able to open, edit, present documents, and switch among applications much faster than on 32-bit Windows.  This is especially true if you run other memory-intensive applications alongside Office.  Of course, your ultimate performance will be determined by the relationship between the amount of virtual memory being actively used and the amount of actual memory installed on your system.

Whether you choose to run 32-bit Office or 64-bit Office, 64-bit Windows 7 or Vista makes a great operating system environment.

What version should you use?

If you’re trying to decide between 32-bit and 64-bit Office, you should ask yourself what your needs are. Are you an Excel power user working with huge amounts of data? Do you need to work with file sizes greater than 2 GB? If so, then you would benefit from 64-bit Office being able to utilize more memory. If not, we’re recommending 32-bit Office 2010 as the default installation on both 32-bit and 64-bit Windows mainly due to compatibility with existing 32-bit controls, add-ins, and VBA (update: most VBA code will work without modification on 64-bit Office, but see this paper more details).

We expect over time for 64-bit Office to become the norm.  Beyond the immediate benefits of supporting larger documents, there will be benefits to having a consistent 64-bit ecosystem for all extensions and controls.  By offering a 64-bit version of Office 2010, we have taken a huge step along this transition path and enabled both customers and partners to be well-positioned for the future.

Installing what you want

If you’re downloading Office 2010 online, then you get to decide what version to download (you can get the other version later if you want). If you buy it on a DVD, both 32-bit and 64-bit versions of Office 2010 will be available. If you install 32-bit Office, for example, and you decide later you want to use 64-bit Office instead, the 32-bit version must be uninstalled (it’s as simple as uninstalling any other program) before installing the 64-bit version.

On the DVD, you’ll notice that the file structure looks like this:


On a computer with no Office products installed, the setup.exe file denoted by the red arrow is the “platform selector.” If you run it, it will automatically install 32-bit Office 2010 by default, even on 64-bit Windows. The only time it will install 64-bit Office is if it detects 64-bit Office already installed on your computer. If you want to install 64-bit Office, then open the x64 folder and run setup.exe from there. Similarly, running the setup.exe file in the x86 folder will install 32-bit Office directly.

You’ll see these instructions if you run setup.exe on 64-bit Windows, select Customize, and click on the Platform tab.


We do not support 32-bit and 64-bit Office versions side-by-side natively on the same 64-bit Windows instance. For example, you will be blocked from installing 64-bit Excel 2010 if 32-bit Outlook 2010 is already installed. This also applies to previous versions of Office, so that 64-bit Project 2010 cannot be installed on the same Windows instance as 32-bit Office 2007. Of course if you are running a 32-bit operating system, you will only be able to install and run 32-bit applications.

You’ll be able to check the version of Office you have by going to the Backstage view (click File tab | Help):


If you want to check what version of Windows you have, right-click Computer, select Properties, and look under “System type.”

Getting to 64-bit Office

What did it take to get here?  Simply telling the compiler to generate 64-bit code was a first, but very small step.  We had to find all the places where pointer differences or buffer lengths were stored in 32-bit values rather than 64-bit values.  We built special tools to examine code for problematic computations that might fail on 64-bit.  We had to find new ways of testing the applications to identify errors that would only arise when the code was running.  Virtually every line of the millions of lines of code in Office needed to be examined for the consequences of this shift.  Many of our tools also needed to be ported as we shifted our default development environment to 64-bit.

We also needed to consider ActiveX controls and components. For example, 32-bit Internet Explorer (IE) can only load 32-bit ActiveX controls, so the 32-bit version of the controls in Office needed to be shipped with 64-bit Office. In addition, there are some components from teams within Microsoft that ship with Office, and we needed to make sure 64-bit versions of these were also available. (For developers: there are exceptions, such as the Microsoft Common Control (ComCtl.OCX) files, which will only be available as 32-bit controls).

What you should know

Both 32-bit and 64-bit versions of Office are largely indistinguishable, except that 64-bit Office has a much higher memory capacity. As mentioned above, the extra memory capacity comes at the cost of some compatibility with existing extensions to Office, such as 32-bit versions of ActiveX Controls and some 3rd party add-ins, in addition to 32-bit versions of programs that interface directly with Office. New versions of these extensions will need to be obtained, and it will take some time for 64-bit compatible extensions to be made available.

For these reasons, we recommend running 32-bit Office 2010 even on 64-bit Windows operating systems for better compatibility. On 64-bit Windows, more applications and documents may be opened at once, and switching among them will be faster because the machine can have more physical memory for the processes to share. When the 64-bit ecosystem for Office is more mature, you’ll be able to easily migrate to 64-bit Office!

Ted Way,

Program Manager, Product Lifecycle and Engineering Excellence (PLEX)

Microsoft Office

2/26 Update: Most VBA code will work without modification on 64-bit Office, but see this paper more details. (this statement has been added above as well)