R610 Memory - Installed Capacity for OS seems low

Hi,

Recently we purchased a PE R610 with 196 GB of memory installed by Dell.  The Dell OpenManage Server Administrator shows the 12 DIMMs registering properly and in the section titled "Total Memory Array(s)" Installed Capacity and Maximum Capacity each indicate 196 GB, but "Installed Capacity Available to the OS" shows 131 GB.

Is this related to the "Memory Operating Mode Configuration" running as "Spare"?  I don't see anything in the "R610 Systems Hardware Owner’s Manual" about this mode configuration.

The plan is for this server to run W2008-R2SP1.

Is there a good reason not to have more memory available to the OS?  How do I increase it?

Thanks,

Ben