What is the maximum amount of memory any single process on Windows can address?

Question

What is the maximum amount of memory any single process on Windows can address? Is this different than the maximum virtual memory for the system? How would this affect a system design?

Vulpes · Answer

32-bit windows has a maximum virtual address space of 4 GB. The OS reserves 2 GB for itself and the other 2 GB is available for user processes. However it is possible to reconfigure this so that 3 GB is available to user processes and only 1 GB is reserved for the OS. To do this you need to specify the /3GB switch in your boot.ini file. There is also a processor feature known as Physical Address Extension (PAE) which allows some 32-bit server versions of Windows to access larger amounts of physical RAM (up to 128 GB). However, this does not change the virtual address space which is still limited to 4 GB. 64-bit windows has a much larger virtual address space of 8 TB. However, a 32-bit process running on 64-bit windows (using WOW) will still be constrained to 4 GB though the system can be configured so that all of this is available to a user process. The maximum amount of physical memory depends on the Windows version being used - between 8 and 192 GB on Windows 7. Currently, if you're designing an application which will run on as many windows platforms as possible, you need to think in terms of no more than 2 GB being available to your process which in practice could be reduced to around 1.4 GB when the necessary dlls etc. are loaded. Having huge amounts of data in memory at any one time should therefore be avoided and you may need to implement a buffering system if you need to process data of this magnitude.

Vulpes · Answer

Well, it's a long time now since I made that post but I have a vague recollection that there was an MSDN article which helped me with some of the details. The chances are that the original article has gone but I found the following link (and sub-links therefrom) which appears to be covering similar ground: https://msdn.microsoft.com/en-us/library/windows/desktop/aa366718(v=vs.85).aspx

Mohit Sharma · Answer

Thanks i was searching for this answer for long period. Although it is bit late, but can you provide some resources for the same as well

What is the maximum amount of memory any single process on Windows can address?

Answers (3)