RGB signaling refers to the method of dividing an image signal to the fundamental three colors (Red, Green and Blue) when processing the signal. It has the advantage of good color division and conveyance, but the disadvantage of requiring at least 3 color division data.
YUV signaling refers to the method of expressing an image signal by the vertical and horizontal signal synchronization (Y), and its color signals (U, V). Color division and conveyance qualities are inferior compared to the RGB method, but the YUV method can express more diverse colors using less image data.
The choice of both methods are available on DVR. RGB image will have clearer color but more 'blocks' on the image, while with YUV image dividing between colors can be more difficult but you will get a more smoother looking surface from them.

30fps DVR board means 30 shared frame rate. What that means is a 30fps DVR board is 30 frames per second over the entire number of cameras being displayed. Therefore, a 4-channel DVR board sharing 30 frames may yield approximately 7.5 image per second per camera.

The capacity of the digital video recorder - that is, the number of hours of video it can contain at a time - depends on what kind of channels you are recording (different signal types take more or less DVR space). Your DVR will record and store up to 25 hours of standard definition programming and up to 10 hours of high definition programming. Because you will likely record a combination of different channels, the capacity will vary. The Interactive Program Guide has several features to notify you when you are nearing the limit of DVR capacity, and allows you options for removing old programs, etc.