How much RAM can Rapidform use with a 32-bit or 64-bit operating system?

XOR/XOV/XOS 32-bit versions can use a maximum of 2GB (by default) or optionally 3GB. The 64-bit versions can theoretically use an “unlimited” amount of memory that is available by Windows.

So generally speaking, the memory limit of Rapidform depends on the memory limit of Windows.

Windows XP 32-bit is restricted to a total of 4 GB, which is, by default, equally divided between Kernel and application usage. Using the /3GB switch in the boot.ini file forces Windows to limit the kernel to the upper 1GB and provides up to 3GB for applications. Windows XP x64 can support much more memory. The theoretical memory limit that a 64-bit computer can address is about 16 exabytes (16 billion gigabytes), Windows XP x64 is currently limited to 128 GB of physical memory and 8 TB of virtual memory. In the future this limit will be increased as hardware capabilities improve.
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2^32 = 4,294,967,296 bytes
4,294,967,296 / (1,024 x 1,024) = 4,096 MB = 4GB (gigabytes)

2^64 = 18,446,744,073,709,551,616 bytes
18,446,744,073,709,551,616 / (1,024 x 1,024) = 16EB (exabytes)
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See http://msdn.microsoft.com/en-us/library/aa366778.aspx for more info on memory limitations for each Windows OS version.