Maximum Java heap size of a 32-bit JVM on a 64-bit OS

Question

The question is not about the maximum heap size on a 32-bit OS, given that 32-bit OSes have a maximum addressable memory size of 4GB, and that the JVM\'s max heap size depen

Answer 1

As to why a 32-bit JVM is used instead of a 64-bit one, the reason is not technical but rather administrative/bureaucratic ...

When I was working for BEA, we found that the average application actually ran slower in a 64-bit JVM, then it did when running in a 32-bit JVM. In some cases, the performance hit was as high as 25% slower. So, unless your application really needs all that extra memory, you were better off setting up more 32-bit servers.

As I recall, the three most common technical justifications for using a 64-bit that BEA professional services personnel ran into were:

1. The application was manipulating multiple massive images,
2. The application was doing massive number crunching,
3. The application had a memory leak, the customer was the prime on a government contract, and they didn't want to take the time and the expense of tracking down the memory leak. (Using a massive memory heap would increase the MTBF and the prime would still get paid)

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