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* Due to various additional constraints such as available swap, kernel address space usage, memory fragmentation, and VM overhead, in practice the limits will vary.
Research
According to, Software - Practice & Experience archive Volume 36 Issue 1, January 2006,
We conclude that the space an object takes in the heap in 64-bit mode is 39.3% larger on average than in 32-bit mode. We identify three reasons for this: (i) the larger pointer size, (ii) the increased header and (iii) the increased alignment. The minimally required heap size is 51.1% larger on average in 64-bit than in 32-bit mode. From our experimental setup using hardware performance monitors, we observe that 64-bit computing typically results in a significantly larger number of data cache misses at all levels of the memory hierarchy. In addition, we observe that when a sufficiently large heap is available, the IBM JDK 1.4.0 VM is 1.7% slower on average in 64-bit mode than in 32-bit mode.
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