VGA vs. DVI
VGA and DVI are very different signals and can even output video at very different qualities as well. Out of all the video interfaces that are available VGA and DVI are found on computers more often than any others. One of the biggest differences between VGA and DVI is that VGA is an Analog signal and has been around for quite some time and DVI is a Digital signal that is newer and is being used more often.
As you can see in the photos below the pin layouts are significantly different between VGA and DVI and they must be plugged into their appropriate connection.
DVI has many more types of pin out connections to differentiate between from to make sure it is compatible with the setup you are trying to accomplish while VGA has only one type of pin out on it.
DVI-Digital Video Interface
DVI is a popular video interface that can send digital or analog video between sources and displays. It is replacing VGA as the standard video connection between computers and monitors. There are several different versions of DVI, with differing compatibility.
The standard connection is DVI-D (Digital) It uses three rows of eight pins for dual link, or two groups of nine pins for single link. Both have a wide "blade" connector that can easily identify the port as DVI. This connection can send digital video only, it is not compatible with VGA, component or any other analog signals. The DVI-D connection is popular for the digital input on LCD monitors. DVI-D dual link is often used in home theater connections for HDTVs cable boxes or HD players. DVI-D single link can send an identical video signal to HDMI (without the audio).
DVI-A supports VGA signals with simple adapters or cables. There is no dual link version of DVI-A, however it can support resolutions higher than the 1920 x 1200 single link max. Note the 4 pins surrounding the wide blade connector. They are often referred to as the "Analog pins" and make up the red, green, and blue video signals, as well as one of the synch lines.
DVI-I (Integrated) can carry both digital and analog signals (though rarely at the same time). Most computer video cards will have DVI-I ports, and many projectors use DVI-I with support for digital or analog video. DVI-I also has the single and dual link variants.
Quality
Analog DVI is the same as VGA in regards to quality, distance limitations and responsiveness. Digital single link video can support resolutions up to 1920 x 1200. Dual link DVI-D can support higher resolutions (such as 2560x1600 used on 30" monitors)
Better than
Composite,S-Video, and Component.VGA is the same as DVI-A transmission.HDMI is the same as DVI-D single link, but doesn't have the dual link or analog options (although HDMI does carry audio)
Applications
Increasingly popular on desktop computers, especially with add-on video cards. Video cards typically use the DVI-I variant, which can be easily converted to VGA or HDMI. Many LCD monitors now have both DVI-D (digital) and VGA monitor connections. Some older HDTV and HD players use the DVI connection. These are almost always DVI-D dual link connections, although only using single link (digital) video.
Conversions
Simple conversions require only a passive adapter or cable, there is no active conversion simply different pinouts of the same signals.
Complex conversions require active circuitry to convert the signal, to change it to the new signal. These often only work one-way.
