Why can't I get a larger heap with the 32-bit JVM?
The maximum theoretical heap limit for the 32-bit JVM is 4G. Due to various additional constraints such as available swap, kernel address space usage, memory fragmentation, and VM overhead, in practice the limit can be much lower. On most modern 32-bit Windows systems the maximum heap size will range from 1.4G to 1.6G. [...] On 64-bit operating systems running the 32-bit VM, the max heap size can be higher
So at least 1.4GB, and it may scale up to 1.6GB or slightly higher if on x64 Windows and still using 32-bit Java.