RGB connection is an old standard used by workstation video monitors. It uses the same signals as VGA but instead of using a single cable carrying all the wires together and using a single connector with all signals, it uses a separated cable for each signal. With a separated cable, each signal has its own shielding, protecting it from interference, which does not occur on VGA cable. Because of that, RGB connection offers a better image quality.

At least in theory: since this standard can only be used with old video monitors that accept this kind of connection, the image quality is limited by the age of the video monitor (newer video monitors offer a far better image quality than older video monitors because the technology used) and the screen resolution. Also, most of these old RGB video monitors run at a different scanning frequency than VGA, making it impossible to connect older video monitors that use this standard directly to your video card.

So, we put this kind of connection here just as a reference, since you probably won’t see it around anymore. Anyway, if you are curious about this standard or happen to have an old RGB video monitor, take a look on this link, you will find it very useful: http://www.epanorama.net/documents/vga2rgb/.

Actually there are three different RGB cabling standards:

• RGB5: The one we mentioned on first paragraph; it uses five cables: red, green, blue, horizontal sync (Hsync) and vertical sync (Vsync).
• RGB4: Uses four cables: red, green, blue and composite sync (Csync).
• RGB3: Uses three cables: red, green + Csync and blue, also known as sync on green.

Each one of these cables use a BNC connector.

click to enlarge
Figure 22: Example of a RGB5 cable.

In summary, the RGB connection type is better than VGA, but because of the age, modern video monitors offer a far better image quality than these old RGB monitors.