Ever since I became equipped with a computer, I always believed the ports on the back of your graphics card have been more or less the same. Most monitors used VGA, so I always plugged into my VGA port.
Yet, there really is a difference between VGA and DVI monitor ports. VGA stands for Video Graphics Array which was introduced in 1987 and transmits analog singnals. Analog signals are typically lower quality when it comes to computer video cards.
According to Wikipedia, analog signals are:
Dealing with a continuous spectrum of values as opposed to a discrete on/off value.
Digital signals, on the other hand, are defined as:
A digital system uses discrete (discontinuous) values, meaning the signal is either on or off.
DVI stands for Digital Visual Interface and transmits a digital signal instead and is mostly compatible with HDMI, the main differences being that HDMI ports are less clunky (they are small compared to DVI). This means that basically, if you use a DVI cable you will get a crisper picture and a higher quality picture on your display.
CRT monitors don’t have DVI ports because the nature of CRT monitors makes them analogous. Lower-end LCD screens may also lack DVI ports, but it’s always a great idea to check if your screen supports the DVI standard. Also, if you computer uses HDMI, but doesn’t have a DVI port, you can buy little HDMI to DVI adapters so you can use DVI with your screen.