The 32 bit version of access limits 2GB size, 32,768 objects, etc. and if we use a SQL backend to an Access frontend we can scale 'our database to hundred of users and we don’t need to use the 2GB jet databases. There are certain limitations while we use 64 bit microsoft office. For example, even if we have the source code for the vb6 applications, we cannot use the 32 bit version dll in 64 bit versions. Though microsoft recommends to compile the source code to 64 bit, there is no option in VB6 to create a 64 bit dll. (There is no 64 bit compiler for VB6) we need to find a work around for this. For eg. http://blog.mattmags.com/2007/06/30/accessing-32-bit-dlls-from-64-bit-code
When you need to access data in *.mdb/*.accdb with 64-bit, the MS Access database engine must be 64-bit, which wasn't available originally until recently. So, yes, you can write application, be it COM based (or VBA), or .NET based to access data in *.mdb/*.accdb for 64-bit, as long as the running computer has 64-bit MS Access database engine installed. The controversial part is, most computer users may have 32-bit MS office installed in the 64-bit Windows (as MS recommended), which would prevent 64-bit MS Access database engine being installed.
Office 2010 also provides support for 32-bit Office 2010 applications that run on 64-bit Windows operating systems by using Windows-32-on-Windows-64 (WOW64). WOW64 is the x86 emulator that enables 32-bit Windows-based applications to run seamlessly on 64-bit Windows systems. Office 2010 lets users continue to use existing Microsoft ActiveX Controls, Component Object Model (COM) add-ins, and Visual Basic for Applications (VBA), which are primarily 32-bit because no 64-bit versions are available yet for many add-ins. Supporting 32-bit Office 2010 applications that run on 64-bit operating systems allows for better compatibility with controls, add-ins, and VBA.
The recommendations for which edition of Office 2010 to install are as follows:
• If users in your organization depend on existing extensions to Office, such as ActiveX controls, third-party add-ins, in-house solutions built on previous versions of Office, or 32-bit versions of programs that interface directly with Office, we recommend that you install 32-bit (x86) Office 2010 (the default installation) on computers that are running both 32-bit and 64-bit supported Windows operating systems.
• If some users in your organization are Excel expert users who work with Excel spreadsheets that are larger than 2 gigabytes (GB), they can install the 64-bit (x64) edition of Office 2010. In addition, if you have in-house solution developers, we recommend that those developers have access to the 64-bit edition of Office 2010 so that they can test and update your in-house solutions on the 64-bit edition of Office 2010.
Running Office 2010 64-bit provides the following advantages:
• Ability to use additional memory.
• Excel 2010 can load much larger workbooks. Excel 2010 made updates to use 64-bit memory addressing to move beyond the 2-GB addressable memory boundary that limits 32-bit applications.
• Microsoft Project 2010 provides improved capacity, especially when you are dealing with many subprojects to a large project.
• Enhanced default security protections through Hardware Data Execution Prevention (DEP).
The following issues might affect compatibility:
• Microsoft Access MDE/ADE/ACCDE files Databases that have had their source code removed (such as .mde, .ade, and .accde files) cannot be moved between 32-bit and 64-bit editions of Office 2010. Such databases that are created by using 32-bit Office (any version) can be used only with 32-bit Office, and a database that is created on 64-bit Office can be used only on 64-bit Office.
• ActiveX controls and COM add-ins ActiveX controls and add-in (COM) DLLs (dynamic link libraries) that were written for 32-bit Office will not work in a 64-bit process. As a result, Office 2010 64-bit solutions that try to load 32-bit ActiveX controls or DLLs will not work. Installations of 64-bit Office 2010 will run only 64-bit controls. Computers can have 64-bit and 32-bit controls installed, and Office 2010 64-bit can only run the 64-bit versions of the controls. The workaround for resolving these issues is to obtain 64-bit compatible controls and add-ins or to install Office 2010 32-bit (WOW).
In addition to controls that load into Office applications, there are also Web-based solutions that use ActiveX controls in Microsoft Internet Explorer. Office 2010 64-bit editions install some Office 32-bit client-side controls for supporting solutions in a 32-bit browser (the default browser on current 64-bit Windows systems). The Edit in Datasheet view functionality is not supported if you install 64-bit Office 2010. However, the functionality is available if you install 32-bit Office 2010.
• In-place activation The following issues might occur if there is not a match between the bitness of Office 2010 and registered applications:
o An OLE server might not instantiate in place and might fail to open if the application registered is not the same bitness as the version of Office installed. (For example, if the OLE Server application is 32-bit and the version of Office installed is 64-bit.)
o Inserting an object into an Office 2010 application document might fail in cross-bitness scenarios. (For example if you insert a 32-bit object in a 64-bit Office 2010 application document.)
• Graphics rendering There are differences between the 32-bit and 64-bit Graphics Device Interface (GDI) that might have performance implications because of the lack of MMX support on 64-bit. Intel's MMX technology is an extension of the Intel architecture (IA) instruction set. The technology uses a single-instruction, multiple-data (SIMD) technique to speed up multimedia and communications software by processing data elements in parallel.
• Visual Basic for Applications (VBA) VBA code that uses the Declare statement to access the Windows application programming interface (API) or other DLL entry points will see differences between 32-bit and 64-bit versions. The Declare statement must be updated with the PtrSafe attribute after inputs and outputs to the API have been reviewed and updated. Declare statements will not work in 64-bit VBA without the PtrSafe attribute. New data types are added to 64-bit Office 2010 VBA: LongLong and LongPtr. For more information about VBA, see the “64-bit VBA Overview” and “Declare Statement” articles in the Microsoft Visual Basic for Applications online Help in Office applications.
• Windows Mobile Device Center (WMDC) synchronization WMDC does not synchronize with Microsoft Outlook 2010 if you use the 64-bit version of Outlook 2010. In such cases, an error message displays that states that there is no default mail client or the current mail client cannot fulfill the messaging. WMDC synchronizes correctly with the 32-bit version of Outlook 2010. To synchronize a Windows Phone with Outlook 2010 by using Windows Mobile Device Center, uninstall Outlook 2010 64-bit. Then use the original installer that you used to obtain Outlook 2010 64-bit to install Outlook 2010 32-bit. Outlook 2010 32-bit is the default option.
General feature deprecations
The following feature deprecations might affect compatibility:
• Microsoft Access The Replication Conflict Viewer is removed from both the 32-bit and 64-bit installations of Office 2010. This functionality can still be implemented by using the ReplicationConflictFunction Property. ReplicationConflictFunction is a Microsoft Visual Basic for Applications (VBA) routine in the running database that can be used to resolve synchronization conflicts. For more information, see “How to: Set Properties of Data Access Objects in Visual Basic” in Access 2007 Developer Reference (http://go.microsoft.com/fwlink/p/?LinkId=150854).
• Publisher The Microsoft Works database converter (wdbimp.dll) is removed from both 32-bit and 64-bit installations of Office 2010. This converter was previously used in the Mail Merge functionality to connect to a data source created in Microsoft Works.
• Word Microsoft Office Document Imaging (MODI) and all its components are deprecated for both 32-bit and 64-bit Office 2010.The legacy Equation Editor is not supported on 64-bit Office 2010, but is supported for 32-bit Office 2010 installations (WOW64).
WLL (Word Add-in libraries) WLL files are deprecated for 32-bit Office 2010 and are not supported in 64-bit Office 2010.
Considerations for Outlook applications
Starting with Office 2010, Outlook is available as a 32-bit application and a 64-bit application. The version (bitness) of Outlook that you choose depends on the edition of the Windows operating system (32-bit or 64-bit) and the edition of Office 2010 (32- or 64-bit) that is installed on the computer, if Office is already installed on that computer.
Factors that determine the feasibility of installing a 32-bit or a 64-bit version of Outlook include the following:
• You can install 32-bit Office 2010 and 32-bit Microsoft Outlook 2010 on a supported 32-bit or 64-bit edition of the Windows operating system. You can install the 64-bit version of Office 2010 and 64-bit Outlook 2010 only on a supported 64-bit operating system.
• The default installation of Office 2010 on a 64-bit edition of the Windows operating system is 32-bit Office 2010.
• The bitness of an installed version of Outlook is always the same as the bitness of Office 2010, if Office is installed on the same computer. That is, a 32-bit version of Outlook 2010 cannot be installed on the same computer on which 64-bit versions of other Office 2010 applications are already installed, such as 64-bit Microsoft Word 2010 or 64-bit Microsoft Excel 2010. Similarly, a 64-bit version of Outlook 2010 cannot be installed on the same computer on which 32-bit versions of other Office applications are already installed.
MAPI applications include stand-alone applications such as Microsoft Lync, Microsoft Office Communicator, and MFCMAPI, and service providers such as address book, store, and transport providers. For MAPI method and function calls to work in a MAPI application (except for one Simple MAPI function, MAPISendMail), the bitness of the MAPI application must be the same as the bitness of the MAPI subsystem on the computer on which the application is targeted to run. The bitness of the MAPI subsystem, in turn, is determined by and is always the same as the bitness of the installed version of Outlook
Should I Use Access 64-bit?
In Microsoft's own words, not unless you need 64-bit Excel or Project:
(source: Microsoft White Paper: Improving the Reach and Manageability of Microsoft Access 2010 Database Applications with Microsoft Access Services)
Microsoft warns "We strongly recommend most users install 32-bit version of Office 2010 on both 32 and 64-bit operating systems because currently many common add-ins for Office will not function in the 64-bit edition,"
Even some of Microsoft's own Office plugins are not yet compatible with the 64-bit software
Access databases with their code removed (split data & code in separate files) can’t be shared between 32-bit and 64-bit versions of Office and any VBA code may not be compatible between 32-bit and 64-bit versions, particularly where the code declares API calls to Windows or uses the new LongLong or LongPtr data types introduced in the 64-bit version.
Graphic elements may render more slowly in the 64-bit version of Office because 64-bit CPUs may lack MMX support for multimedia and communications.
Read more: Office 2010 Beta – 32-bit or 64-bit – The Choice is Clear | PC Pro blog http://www.pcpro.co.uk/blogs/2009/11/23/office-2010-beta-%E2%80%93-32-bit-or-64-bit-%E2%80%93-the-choice-is-clear/#ixzz2KfgnH1ZO
The biggest problem by far is that ActiveX controls Add-Ins and COM DLLs written for 32-bit Office will not work with the new 64-bit version. Microsoft are due to release a new VSTO (Visual Studio Tools for Office) runtime which will bridge this gap for DLLs and Add-Ins written using VSTO but it isn’t available yet. Other manufacturers will have to test, possibly change, and re-issue their DLLs and Add-Ins in 64-bit versions to get them to work
Read more: Office 2010 Beta – 32-bit or 64-bit – The Choice is Clear | PC Pro blog http://www.pcpro.co.uk/blogs/2009/11/23/office-2010-beta-%E2%80%93-32-bit-or-64-bit-%E2%80%93-the-choice-is-clear/#ixzz2KfgYkHPe