Why the usable memory is diffrent with system info??

[brucecao]

Hi,

I  I have 48 GB of ram. The System Information is this.

M/B: Sugon 24000649 Version Rev 1.xx - s/n: ST2024011400315

BIOS: American Megatrends Inc. Version 3303. Dated: 10/28/2014

CPU: AMD Opteron™ 4180 @ 2600 MHz

HVM: Enabled

IOMMU: Enabled

Cache: 768 KiB, 3072 KiB, 5120 KiB, 768 KiB, 3072 KiB, 5120 KiB

Memory: 48 GiB DDR3 Multi-bit ECC (max. installable capacity 128 GiB)

But in dashboard memory card show usable memory is 29.4 GiB

Linux 4.19.98-Unraid.
root@Tower:~# free
              total        used        free      shared  buff/cache   available
Mem:       30878936      366904    29677768      732868      834264    29520644
Swap:             0           0           0

Any one can help me?

Thanks