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Notebooks that have video chips that can be removed/replaced are the high end ones like the ones at the links that I attached, do you have link to the notebook that you are considering so that we can take a look.
Both desktop and some notebook computers can have dedicated/discreet video chips but as I have said notebooks that have this option tend to be the high end of the market, some info below;
An integrated graphics processing unit (GPU) doesn't use its own RAM; it utilizes the system's memory instead. So, if you have a computer with 4GB of RAM, the video card can use anywhere between one and five percent of the available memory for graphics processing. Of course, this percentage varies depending on the size of task, especially if you're multitasking or playing a game.
The benefit to an integrated unit is that it is cheaper, which in turn means a less expensive computer. An integrated graphics card also generates much less heat than a dedicated video card and uses drastically less power, which improves the overall battery life. Integrated graphics cards are perfect for people doing everyday graphics processing. This includes watching or editing videos, 2D gaming and general word processing. Such activities aren't graphic intensive, so a low-end video card is ideal. That doesn't mean you won't be able to play 3D games, but you will have to turn down the graphics settings or you'll experience in-game slowdowns.
A dedicated, or discrete, GPU has its own independent source of video memory, leaving the RAM your system uses untouched. If you have a GeForce GTX 680M video card with 2GB of video memory, for example, that memory is completely separate from your computer's 8GB of system memory. Dedicated cards are perfect if you are into serious gaming or are a professional graphic designer.