Q about integrated graphics circuits and dedicated graphics cards

[J.L.]

After surfing several hours on web, trying to find out answer, I'm still
a bit uncertain about following issue:

Are there three types of graphics circuits:

1) Integrated on MB, has an own GPU but no own memory, uses RAM.

2) Integrated on MB, has an own GPU and also own memory, uses this
memory and also "borrows" from RAM.

3) Dedicated graphics card with own GPU and memory, uses this memory and
also "borrows" from RAM.

Earlier, when laptops had only small amount of RAM (like 512 MB), the
benefit of dedicated graphics card (later: DGC) with own memory was
obvious, but now that laptops has usually 2GB-4GB of RAM, is 256MB of
DGC memory really meaningful? Whole other issue is, that DGCs typically
have better other components than integarated graphics circuit (later: IGC).

So, is 2GB RAM + 256MB DGC usually better than 3GB RAM + IGC w/o memory.

Almost all the web sources seem to live in the past, they explain like
"IGC may 'steal' half of your 512MB RAM...".

- J.L.