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MSTS - Helpful Facts and Links - Part 32 (32-bit v 64-bit OS) (Also applies to Open Rails)

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MSTS - Helpful Facts and Links - Part 32 (32-bit v 64-bit OS) (Also applies to Open Rails) Empty MSTS - Helpful Facts and Links - Part 32 (32-bit v 64-bit OS) (Also applies to Open Rails)

Post  slipperman12 Thu 15 Jan 2015, 11:03 pm

Both MSTS and Open Rails are 32-bit programs, so, when run in a 32-bit operating system, can't use more than about 2GB each. The total amount of memory available to programs under a 32-bit OS is about 3.5GB.

Running MSTS under a 64-bit OS won't make much difference to that program, but it might run better because the other 64-bit processes which run at the same time as MSTS will have access to the whole amount of RAM installed.

On the other hand, Open Rails, although it is a 32-bit program, recognises when it is running in a 64-bit OS and automatically implements a procedure called Large Address Aware (LAA) which gives it access to more memory. If you open the Open Rails folder, you'll see RunActivity.exe and RunActivityLAA.exe.

With a 32-bit OS all processes must be accommodated within about 3.5GB; if there is insufficient room for a process to run, additional memory out of the 3.5GB is made available to it by removing a process which is not running and "paging" it out to the Page File, which is normally on the hard drive. When that process is required again, it has to be read from the HD into RAM again, and so it goes on! With a 64-bit OS, the 3.5GB limit is removed to a very high value, which we currently, don't have to worry about. This means that the whole 4GB, 8GB, or whatever amount is installed, is available, to 64-bit programs. Note that LAA won't make the whole lot available to Open Rails (or any other program it is applied to), but only up to 4GB. Although LAA can be applied to a 32-bit OS, it requires the user to make some changes to their system, so it's not recommended, except for those with the appropriate expertise.


1. MSTS might run better under a 64-bit OS, but only because 64-bit processes / drivers / etc., can run outside of the 3.5GB limit.
2. Open Rails should run better under a 64-bit OS, a) because of the above and b) thanks to it being Large Address Aware.
3. Don't expect earth-shattering results if you switch to a 64-bit OS - it'll be very subtle or may even be imperceptible!!
4. If you're NOT going to increase your RAM from 4GB to 8GB, it's recommended that you don't change from 32-bit to 64-bit OS, because the 64-bit OS needs more memory to work.


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