I don't know what happens if you specify "-Xms100". According to the docs, that would mean 100 bytes, but it must be a multiple of 1024. In any case, it's not right and if you mean 100 megabytes, you should specify "-Xms100m".
The default depends on the operating system. For Sun Java 5 on Windows it is 2 MB according to the documentation. [ July 22, 2006: Message edited by: Jesper Young ]