I'm running CentOS 5.1 with all updates, and the xen kernel. For some reason the OS is not seeing the full amount of ram. #uname -a Linux CentOS-VM-A 2.6.18-53.1.21.el5xen #1 SMP Tue May 20 10:03:27 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux # free total used free shared buffers cached Mem: 6104064 3445136 2658928 0 1412236 1515032 -/+ buffers/cache: 517868 5586196 Swap: 2031608 0 2031608 On another box with identical hardware, I see # free total used free shared buffers cached Mem: 5038080 1818980 3219100 0 145208 1148608 -/+ buffers/cache: 525164 4512916 Swap: 2031608 152 2031456 Both of these boxes have 8GB of ram. Is there a reason I'm not seeing all of it? Russ