rendering - CPU - GPU memory data flow

I'm a newbie graphics programmer and I've been wondering recently - how does model data (meshes and materials) flow from application (CPU memory) to graphics card (GPU memory?)? Say I have a static model (e.g. a building) that I load and setup once and don't change throughout the app lifespan.

• Does its data get sent to GPU memory only once and sit there forever?


• When the model gets actually rendered each frame do GPU processors have to fetch its data each time from GPU memory? What I mean is - if I had 2 models rendered multiple times each - would it matter if I first rendered the first one multiple times and then the second one multiple times or if I rendered the first one just once, the second one just once and kept interleaving it like that? I could call this question "internal GPU data flow" in this sense.



• Obviously graphics cards have limited RAM - when it can't hold all the model data necessary for rendering 1 frame I guess it keeps fetching (some of) it from CPU RAM each frame, is that correct?

I know there's a lot of books and stuff about this on the internet but maybe you have some quick general guidelines as to how to manage this data flow (when to send what and how much, when and how to render)?

Edit: I forgot to make one distinction: there's sending the data to the GPU and there's setting/binding the buffers as current. Does the latter cause any data flow?

Edit2: After reading Raxvan's post I'd like to distinct a few actions:

• buffer creation with initialisation (as he said I can store the data in either CPU ram or GPU one)


• buffer data update (which I believe is straightforward when the data is kept in CPU ram and requires fetching from GPU to CPU ram (and then back) when it's kept in GPU ram)


• binding the buffer as active (is it just a way to tell the API that I want this buffer to be rendered in the next draw call and it doesn't do anything by itself?)


• API draw call (here I'd like to hear from you what actually happens there)