OVM guest VM does not show all assigned memory
I am using OVM 3.3.3 and I have 2 servers as a pool, in the pool I have a 2VMs as somain type HVM running with 16GB and 25GB, I have created 2 more VMs,this time are XEN_PVM I have assiged 16 and 32 GB (I have oracle Linux 5.9 32 bits installed on each), after start them up I noticed that none of them are showing the full memory that was assigned ,.. it is showing only 8GB,.. why?