No, it is not using all of the memory since it has to reserve memory
address space for I/O controllers that have their own onboard memory and
also which sometimes need shared memory to transfer data.

http://support.microsoft.com/kb/929605/en-us

"Barrie" wrote in message
...
I am using Home Premium and recently increased my desktop memory from 2GB
to
4GB. The BIOS sees each of four motherboard slots with 1.024GB and
reports a
total of 4096GB. System information reports seeing only 3.325GB. Can
someone please tell me what is going on? Is Vista not using all the
available memory?