The address space is limited to 4 gigabytes (GB) for 32-bit computer systems. Of those, 2 GB are reserved for the operating system. The other 2 GB are available for applications. The amount of memory space that is actually available for calculations is reduced further by applications that are loaded by the operating system.
For 64-bit systems the address space is limited to 16 terabytes (TB). Of those, 8 TB are reserved for the operating system. The remaining 8 TB are available for applications.The only factors limiting usable memory size are the available hard drive capacity and the acceptable calculation time.