If I have Intel i7 7500U HD Graphics 620 (1.7GB graphic memory aveilable) and a third party GPU that contains 2GB (VRam) of Graphic memory on my laptop, Are those 3.7GB of graphic memory as total will be available for my graphic work?
I had an answer about this Issue. In my case, It is depends on whtere graphic card has that technology called Optimous Technology and also the laptop has that technology to use both of the VRAM at the same time.
In most cases to my knowledge with intel cpu's, either the integrated graphics or the dedicated graphics card is being used. This means that whichever device is being used at the moment determines how much vram you have.