We are considering upgrading two of our Windows servers from 32 bit to 64 bit and put 32 GBs RAM on them.
Will Domino 32 bit - and eventually Notes - take advantage of all the RAM available to the OS or will we need to install Domino 64 bit?
Many thanks
Mael
Subject: Domino 8.5.1 32 bit on Windows 64 bit
32 Bit Domino on 64 Bit Windows will only be able to use 4 GB of memory. In order to use all available memory you will have to use 64 Bit Domino on 64 Bit Windows
Subject: Domino 32 bit
Many thanks, James.
Subject: Just be sure to check technotes on Win 64
There is an issue running Domino in a Win 64 environment. Seems the OS doesn’t handle the file cache well. You should search the technotes for runnign Domino in Win 64. I believe there is a notes.ini parameter as a workaround.
Here is one link to look at
Subject: Good reading…
Didn’t know you had to resource to this hack.
Thanks again, James.
Subject: 8.5 Domino 64-bit running fine in 2003 64-bit
So far I’ve been running Domino 64-bit on windwos 2003 64-bit since last year (starting from 8.01 to 8.5) and it’s working perfectly well.
And I’ve just upgraded it to 8.5.1 last week. So far so good.
Subject: yes, 32 bit Domino will take advantage of 64 bit Windows and more memory
32 bit programs on 32 bit Windows each have 2GB of available address space because the OS takes up 2GB for the kernel and the summation cannot exceed 4GB. 32 bit programs on 64 bit windows get the full 4GB address space as available memory because Windows has the rest of the 64 bit address space for it’s kernel portions. So, this means you go from 2GB to 4GB available memory for each Domino process. Since a Domino partition consists of many processes this means you can use even more memory.
An example domino partition - running just a few of our standard programs (there are many more, I have a server up running now and it has 15 processes running in the partition):
server
http
amgr
router
replica
on 32 bit Windows each would only have 2GB available so the max memory they could use would have been 2+2+2+2+2 = 10GB and the kernel would have been using some amount of memory for each but not necessarily 2GB each. on 64 bit Windows each will have 4GB available so the max memory each can use goes to 4+4+4+4+4 = 20GB of memory.
Many people forget that a Domino partition is made up of many processes and each process has it’s own address space and therefore we can/are able to use use more than 4GB of memory on a system 
For performance and to reduce our memory consumption we do make use of shared memory between our programs so that 20GB of memory may come down to 16GB if you say we are using 1GB of shared memory in each process, and for 32 bit if 1GB of shared it would go from 10GB to 6GB of actual physical memory in use.
The point to take is, yes, 32 bit Domino on 64 Bit windows can/will take advantage of more memory in multiple ways.
Thanks!