Windows 10 strikes again. It uses quite a bit of GPU VRAM for its own internal needs. Here is the list of possible solutions in order of increasing dificullty:
   * You have to add the following command-line options in order to minimize VRAM usage: -rvram -1 -eres 0
   * Usually Windows 10 grabs memory only from the GPU that is connected to a display, so connect your display (or the display plug) to the iGPU of the motherboard (if you are using Intel motherboard). On multi-GPU rigs, you can also put an old (unusable for mining) GPU and connect the display to it.
   * The heavy-duty solution is to switch to Linux but it has its own problems. This will buy you about 5-9 additional months of operation until the DAG grows too big to fit in 4 GB VRAM.

   Note for Linux users: the latest AMD Linux driver (19.30-855429) is not supported by PhoenixMiner 4.5c. For now, stick with 19.30-838629. We will release 4.6 shortly (in a week or two), and it will contain some goodies for Linux, including advanced hardware stats, and hardware control for AMD cards.