楼主可以看一下对websphere的描述。
For IBM on the 32-bit Windows platform, the maximum heap size we could use was 1640 megabytes RAM (the theoretical limit is 2048 megabytes or ~2 gigabytes, however we found the default install of WebSphere will not start on 32-bit Windows with a heap size greater than 1640 megabytes, possibly due to the fact the JVM requests a contiguous block of memory for the heap, and Windows 32-bit doles out up 1,640 megabytes of contiguous memory per process). On Linux, we were able to configure the 32-bit WebSphere heap size to 2,300 megabytes of RAM, which represents more RAM available for cache entries on Linux vs. Windows for 32-bit WebSphere. For 64-bit WebSphere on Windows, we were able to run with a heap size of 14,500 megabytes without incurring OS swapping. For 64-bit WebSphere on Linux, we were able to also run with a heap size of 14,500 megabytes without incurring OS swapping (see the heap size setting discussion for a more detailed explanation). For WebSphere, we found the maximum number of entries allowed in the cache (within a margin of roughly 500 entries) via trial and error -- simply by running with an estimate of 500K per entry up to available heap size, then running the test with a max cache entry value until we found the point at which WebSphere would not crash/heap dump. For 32-bit Windows/ WebSphere, this number was 2500 entries. For 32-bit WebSphere on Linux this was 3000 entries. For 64-bit WebSphere the numbers were 27,000 allowable cache entries on both Windows 64-bit and Linux 64-bit, respectively given our matching configured Java heap sizes on these platforms.