See the default values of various sizes set by a J9 VM, with -verbose:sizes

gistfile1.txt

$ java -version
java version "1.6.0"
Java(TM) SE Runtime Environment (build pxa6460sr8fp1-20100624_01(SR8 FP1))
IBM J9 VM (build 2.4, JRE 1.6.0 IBM J9 2.4 Linux amd64-64 jvmxa6460sr8ifx-20100609_59383 (JIT enabled, AOT enabled)
J9VM - 20100609_059383
JIT  - r9_20100401_15339ifx2
GC   - 20100308_AA)
JCL  - 20100624_01
$ java -verbose:sizes
  -Xmca32K        RAM class segment increment
  -Xmco128K       ROM class segment increment
  -Xmns0K         initial new space size
  -Xmnx0K         maximum new space size
  -Xms4M          initial memory size
  -Xmos4M         initial old space size
  -Xmox512M       maximum old space size
  -Xmx512M        memory maximum
  -Xmr16K         remembered set size
  -Xmso256K       operating system thread stack size
  -Xiss2K         java thread stack initial size
  -Xssi16K        java thread stack increment
  -Xss512K        java thread stack maximum size