The 'Rb' at the end of a resolution description means 'reduced blanking'.

To explain this further: analog RGBHV signals (and YPbPr) need some time after the horizontal sync in order to 'clamp' the black level - i.e. to sense the lowest (black) point in the video signal. This is the main reason for the blanking time in video signals.

However, DVI signals require no such thing - they already have the pure absolute digital number that represents the brightness of Red, Green and Blue and thus don't need to work out the lowest point - since that's known to be just 0.

Thus, DVI signals can get away with far less blanking time as no clamping is requires - 'reduced blanking'. They still need some in order to give the display time to move to the next line on the TFT screen, but nowhere near as much as an analog signal.

The vertical blanking time can also be reduced, since modern displays do not require so much time to 'retrace' back to the start of the image again.

An analog 1920x1200@60Hz signal requires a pixel clock rate of about 193MHz, but for DVI this can be reduced to around 154MHz by removing most of the blanking time. This allows resolutions to be sent over DVI that would otherwise have gone beyond the 165MHz limit.

Some C2 units now support up to 2880x900 pixels over a single DVI link - all because of the reduced blanking time that's possible over DVI.