After a bit more research --
http://www.sun.com/products-n-soluti...16-4379-10.pdf
on page C-18 Sun states:

Quote --
The CPU L2 cache megacell reserves a 4 Gbyte region for cacheable main
memory.
The memory controller only supports 4 Gbytes of space.

----------------------------------------------------------------------------------------------------------------------------
Note - Although the cache and memory controller support up to 4 Gbytes,
only
512 MB DIMMS are supported on the Sun Blade 150 system. This limits the

maximum DIMM configuration to 2Gbytes.
-----------------------------------------------------------------------------------------------------------------------------

-- Quote


So we are only able to use 2GB on the system.


Mike