Domino 32 bit vs 64 bit – how to decide

I my last post I talked about what the main advantage of going 64 bit Windows for Domino – shared addressable memory – but I really did not go into detail on whether 32 bit or 64 bit Domino is the better choice for an installation.

As I mentioned previously, the main advantage of going 64 bit Windows is that your Domino instance will not have 4 GB of addressable shared memory available. The kicker is that this holds true for both 32 bit and 64 bit Domino on 64 bit Windows. This fact came as quite a surprise to me when I found out, this is due to the way that the Domino memory system and the memory handles are currently designed.

So the question becomes, why would I choose 64 bit Domino if 32 bit does the same for me?

Personally, I believe the main deciding factor is whether you plan to run add-in tasks in your Domino instance or not. To run an add-in task on a 64 bit Domino server the add in task also needs to be 64 bit. To run an add-in task on a 32 bit Domino server the add-in task needs to be 32 bit as well.

The logical conclusion therefore is: if you plan to run ANY add-ins (e.g.: Anti Virus, etc.) on your 64 bit Domino server you need to determine if that program is available in 64 bit as well. If it is and any other products you might consider running are available in 64 bit as well – then you can go ahead (but test first anyway – of course!!) and install 64 bit Domino. If this is not the case your choice will need to be 32 bit Domino.

“Elementary, my dear Watson.”

5 thoughts on “Domino 32 bit vs 64 bit – how to decide

    • Thanks for your comment! This technote is addressing different issues – what I am talking about is addressable shared memory, not total system memory. To give you a simplified picture: shared memory is basically a bubble that Domino captures and allows other programs that have to talk to Domino processes to access when it does not require that memory itself. Whereas the technote rightly state that you have more access to total system memory (beyond the 4 GB for normal 32 bit programs) you do not gain anything in terms of addressable shared memory. These are two different things. Each individual Domino task is essentially a program that gets it’s own reserved memory and also accesses shared memory and that shared memory is actually key. If you try to push the usage of shared addressable memory beyond 2 GB on a 32bit Dom/32bitWin server your machine will crash. If you put that same server instance on 64bit Windows it will be fine. IBM does some very intensive testing and up until now has not seen the usage of shared address space go beyond 4GB on just about all of the test scenarios they run. They do have tools that will go in and gobble up free shared memory to simulate an issue and crash the server (I have seen them do it during testing at my current client).


  1. Memory isn’t the only thing that changes with 64Bit. A mail server even hardly hammered will barely need all that memory. However what also changes is the I/O structure. In a 64Bit environment you have 64Bit I/O paths and so reading/writing data improves (you probably see that only under heavy load).
    If you run applications – many of them – you will benefit from memory. For mail or a few standard apps I/O is the big winner.


    • I/O is always important on a Domino server – insufficient i/o performance is the most common root cause for user perceived bad performance. Paul Mooney does a very good presentation on the importance of i/o on servers. However, the improved i/o might not be as important as the ability to run the third party app (e.g. Anti Virus, server administration add-ins,etc.) which might be mandated by either policy (such as AV on all mail servers) or by business (a 3rd party add-in that enabled business processes, etc.). That is why I put the requirement for availability of 32 bit vs 64 bit add-ins at a higher rank than the other – quite obvious – advantages that you can realize from a 64 bit Windows OS.


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