That board has a onboard GPU so some memory will be 'stolen' so it can be used by the graphics:
Here's a review from Hardware Secrets:
Let’s take a look at the Gigabyte 880GMA-UD2H, a micro-ATX, socket AM3 motherboard from Gigabyte based on the AMD 880G chipset, featuring five SATA-600 ports, two USB 3.0 ports, and two PCI Express x16 slots.
We have already posted a detailed comparison between AMD chipsets with integrated video. In summary, the AMD 880G chipset is based on the Radeon HD 4250 graphics engine, which is a slower version of the graphics engine used on the AMD 890GX (Radeon HD 4290). Normally, the AMD 890GX uses a new south bridge chip, called SB850, and the AMD 880G uses the older SB710 south bridge. SB850 natively supports SATA-600 ports (a.k.a. “SATA 6 G”) and it is the first chipset with this feature (currently on motherboards based on other chipsets featuring SATA-600 ports an external controller chip must be used). Gigabyte used the SB850 south bridge instead of the SB710 on the 880GMA-UD2H, so this motherboard offers the native SATA-600 ports.
As you may know by now, on systems with integrated video the video memory is achieved by stealing part of the main RAM. Chipsets from AMD have a feature called SidePort, which is an optional memory chip soldered on the motherboard in order to increase video memory. The portrayed motherboard doesn’t have this feature.
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