Windows Mixing 32 and 64-bit components in a single MSI

Definetely one my pet peeves about Windows Installer is how it deals with instruction set architectures (ISAs). Looking at Windows NT history, supported ISAs have come (amd64, IA-64) and gone (Alpha, PowerPC, MIPS) – yet most of the time, there was more than one ISA being officially supported. Having to ship binaries for multiple ISAs therefore always has been on the agenda for many ISVs.

Needless to say, supporting multiple ISAs requires special consideration when developing setup packages and providing separate packages – one for each ISA – has become common practice to approach this. This approach makes perfect sense: Given the incompatibility of most ISAs, nobody needs Alpha binaries on a MIPS system or amd64 binaries on a IA-64 machine, so there seems little reason to mix ISAs within a single package.

Unsurprisingly, Windows Installer, which was created somewhere around 2000, also goes this route and encourages developers to provide separate packages for each ISA.

However, with the advent of amd64/x64/IA-32e/Intel 64/whateveryoucallit, the situation has changed: Because i386 and amd64 are so closely related and compatible, there are now plenty of situations where combining binaries of differing ISAs (i.e. amd64 and i386) in a single installer package makes perfect sense. Examples for this include:

  • A package comprises a shell extension as well as a standalone App. For certain reasons (maybe the use of VB6), there only is a 32 bit version of the App. The shell extension, in contrast, is available for both, i386 and amd64. Whether you put everything into one package or provide separate packages for each ISA, one of them will comprise a mixture of ISAs.

  • SDKs for unmanaged code usually include .lib and .dll files for multiple architectures. Shipping separate packages for i386 and amd64 (containing different binaries but the same headers, docs, etc.) may please the Windows Installer gods, but seems redundant, a waste of disk space, and user-unfriendly.

Thanks to the msidbComponentAttributes64bit flag, mixing architectures in a single MSI package is technically possible: You mark the package as being 32 bit and set said flag for all 64-bit components. Rather than splitting your setup into multiple packages, you can conveniently combine everything into one.

When reading the documentation (and ICE requirements, more on this later) carefully though, it turns out that this is not quite what the Windows Installer team invented this flag for. Anyway, it works fine, problem solved.


If only there was not ICE80.

ICE80, alas, is critical if you intend to conform to the Requirements for the Windows Vista Logo Program for Software:

Applications must use the Windows Installer (MSI) or ClickOnce for installation. Windows Installation packages must not receive any errors from the Internal Consistency Evaluators (ICEs) listed here: 1-24, 27-31, 33-36, 38, 40-57, 59, 61-63, 65, 67-72, **74-84**, 86-87, 89-94, 96-99

ICE80 mainly states that (1) you should not install 64 bit components to 32 bit directories (e.g. Program Files vs. Program Files (x86)) and (2) you should not use 64 bit components in a 32 bit package.

(1) is fair enough, although it raises the question where you should install your software to without splitting it in two or violating other ICE rules. Worse yet, (2) effectively means that said way to create multi-ISA packages, creating 32 bit packages with some components marked with msidbComponentAttributes64bit, is illegal alltogether.

So to be logo’ed, there seems to be no other way than providing separate packages, maybe along with (urgh!) a meta-package that installs the other two.

If there are more important things on your schedule than getting a Vista logo, ICE80 seems like something that can safely be ignored. Indeed, this is what I have done several times, including in case of the cfix installer.

Anyway, let’s ignore ICE80 once more and hold on to the plan of building a 32-bit package containing both, 32-bit and 64-bit components.


For an SDK that is installed on 64-bit Windows, it will usually make sense to install both, 32 and 64 bit .lib and .dll files etc. On 32-bit Windows, installing 64-bit components may seem odd, but due to the existence of amd64 compilers for i386, it still makes sense to install them or at least offer them as optional feature.

So far, so good. Things get interesting, though, when COM registration comes into play. Naturally, a 32 bit installer package sees the system like any other 32 bit application does. Most importantly, this means that Registry Reflection and File System Redirection applies.

Now consider a package that contains both a 32-bit and a 64-bit version of some COM server, each installed to a separate directory. COM Registration either be performed through the Class or the Registry table. Provided that the msidbComponentAttributes64bit flag has been used properly, such a package will work great on 64 bit systems thanks to Registry Reflection: The regsitry entries will be written to the proper (reflected) locations and both COM servers will work properly.

Now think what happens on 32-bit Windows: (1) There is no Registry Reflection and (2) Windows Installer silently ignores msidbComponentAttributes64bit flags. Result: The installation will run just as smooth as on the 64-bit system. However, while installing the files continues to works flawlessly, the registry will be left in a less-than-optimal state: Due to the nonexistence of Registry Reflection, the registration entries of both COM servers will have been written to the same location!

Needless to say, the server whose registration entries were written first will now be unusable.

In a way, Windows Installer has taken its revenge for breaking the rules.

Bottom line: Mixing 32 and 64-bit components in a single MSI works fine in many cases, but is against the MSI rules and can lead to further problems. And while I am still convinced that providing separate, ISA-specific packages is wrong or at least inconvenient in certain situations, it is definitely the safer and “right” way to go.

(Note: Windows Installer 4.5 introduced multi-package transactions, which allow reliable and transactional multi-package setups to be built so that splitting a setup into multiple packages can be implemented without much pain. However, very few users already have Windows Installer 4.5 installed and Windows 2000 is not even supported by this release. For many of us, relying on this feature therefore is not really an option.)

Any opinions expressed on this blog are Johannes' own. Refer to the respective vendor’s product documentation for authoritative information.
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