64-bit and you.
64-bit operating systems are becoming very common nowadays. Practically all Windows 7 installations now come as 64-bit by default. Windows 7 is the "tipping-point", the operating system was released right around the same time that the amount of memory installed in a computer became commonly 4GB or more. 64-bit processors themselves predated the memory amounts by a few years but it was the memory and Windows 7's release together that pushed the computing landscape over into 64-bit.
Many applications (including games) however are still 32-bit and there is a huge population of legacy programs that will likely remain 32-bit forever as they will just not be updated. 64-bit systems also have lost the ability to run 16-bit applications unless an emulation layer such as DOSBox is installed and used.
The major benefit a 64-bit operating system together with a 64-bit application provides is the ability to use more than 2GB of memory per instance of the program. 32-bit programs by default are limited to 2GB of total memory - even on 64-bit operating systems - that the program can use. 64-bit programs can also be slightly faster than their 32-bit equivalents because when a program is running in 64-bit mode that program has access to extra "registers" or "scratch-pad-variables" so that it can keep more temporary variables inside the processor itself instead of having to fetch and store them into system memory which is outside the processor.
Occasionally some applications - 32-bit ones - can really benefit from having more than 2GB of memory available to them. On 64-bit systems there is a "application flag" that can be set on 32-bit programs to allow them to use up to 4GB of memory. This flag is called "Large Address Aware." At the beginning of every program's file there is a bunch of settings that tells the operating system how a program should be executed. The LAA flag is one of those and if set then the operating system will allow a 32-bit program to use up to 4GB of memory. This flag is already set on some popular applications such as Civilization V and Crysis 2. So those programs under 64-bit operating systems can use up to 4GB of memory if it is available.
You can set this flag yourself. There is a utility to do so: here. However, you should not just go out and randomly use this utility on all of your programs. Most programs when they are in their design phases are programmed in such a way that they will stay within the 2GB of memory limit. It is when you are modifying programs such as adding high-resolution-texture-packs and such that you might want to use this utility to set the LAA flag. Remember: many programs - especially games - come with DRM and modifying the executable to set this flag may cause the program to stop working. Therefore you should always make a backup of any file you try this utility on just in case you need to restore the file in case of failure. If you don't do this, and also worst-case, you may end up needing to reinstall the application.
The Large Address Aware flag can also be used on 32-bit systems which have 3GB of memory installed in them but I will not recommend that you try this utility if you are on a 32-bit system. The reason for doing so is because you would need to modify an operating system setting in addition to using this utility and if that is not done properly then your operating system may not work correctly or at all. So, using this utility in a 32-bit setting: advanced, and cautioned, users only.
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