I post it here as it was tested on the free demo version at my work....my license is on my private PC..
Here at work we have an FX5800 4GB....Octane doesn't show the available memory on the device manager...it says 0mb and does not show the different memory usage neither.
in revenge under the render viewport it shows the memory usage/0mb.... too much memory or a simple bug?
Octane Render 1.021 beta2.1 released [OBSOLETE]
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Core i7 990x|GTX 580 3GBram|PNY GTX275|24GB ram|Win 7 64Bit....and the wonderful Octane 
Most probably a bug. I have noticed the same on my own system, and some other posts speak about weird memory amount displayed.
French Blender user - CPU : intel Quad QX9650 at 3GHz - 8GB of RAM - Windows 7 Pro 64 bits. Display GPU : GeForce GTX 480 (2 Samsung 2443BW-1920x1600 monitors). External GPUs : two EVGA GTX 580 3GB in a Cubix GPU-Xpander Pro 2. NVidia Driver : 368.22.
