What is an OpenGL RBO?

I just read the following presentation 开发者_Python百科which seemed to recommend RBOs over PBOs for GPU->CPU transfers. I have been looking for some source explaining RBOs, without success.

Anyone know of a good source explaining RBOs?

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From opengl wiki:

Renderbuffer Objects are OpenGL Objects that contain images. They are created and used specifically with Framebuffer Objects. They are optimized for being used as render targets, while Textures may not be.

more information here

An example on gamedev.net here (have a look at "Adding a Depth Buffer" section)

EDIT

When you render to a frame buffer you can choose between two types of framebuffer-attachable images; texture images and renderbuffer images. In the former case you will render to texture the frame buffer, in the latter you will obtain an offscreen rendering.

Here is a discussion on the difference between this two kind of frambuffer-attachable images.

Here you can find more information about FBO and attachable images.