First things first, let's clear out some of the confusions.
VGA stands for Video Graphics Array and is a type of analog video signal, and it is also the name of the cable and the port fort VGA. It is most commonly used for connecting a monitor to a computer, but there are other uses for it as well.
HDMI stands for High Definition Multimedia Interface. It is the name of the standard and also the name of the cable type used. A HDMI cable can carry both video and audio signal, so it is a type of a combined AV cable. The signals in this cable are purely digital. It transmits signal in the form of a digital stream of zeros and ones.
DVI stands for Digital Video Interface and is the successor to the VGA standard. Just like HDMI, and as the name suggests, this one also carries digital signal. But unlike HDMI it can only carry video information, no audio. However, some equipment can support both analog and digital video signals over DVI. So the video signal in DVI can be either digital only, or digital and analog. If digital only then it will say "DVI-D" in the specification where D is for Digital, and if the equipment supports both digital and analog then it will say "DVI-I" where I is for "Integrated" meaning it integrates both analog and digital video. You would then buy your DVI cables accordingly. But remember, there is no audio in DVI.
So now that you know the difference between VGA, HDMI, and DVI, it makes things easier to understand. Since VGA carries only analog video, you would need a processor to convert that signal to a digital stream, so that you can get a working HDMI connector on the other side.
- So it's like VGA (analog) > processor (AD converter) > HDMI
And it's similar when you go from HDMI to VGA, it's just the other way around. You start with a digital stream, it enters a converter that makes it into analog video signal, and then you get your working VGA on the other end.
- So it's like HDMI (digital) > processor (DA converter) > VGA
I'm not sure what kind of cable or converter you got there. But you need to make sure it is one of the "active" type. Meaning it needs to have a power supply for it to work.
I will give you an example with DVI and VGA on a TV.
Say you have a free DVI port on your computer! And you want to connect your computers DVI port to the VGA port on your TV so that you can watch movies on the TV, or do whatever. Remember, DVI ports can be digital only or integrated (analog and digital in one). If your computer has a DVI-I port you can get a DVI-I to VGA cable and connect them and you should get a picture immediately. This is because the DVI-I port carries analog signal.
- So it's like this, DVI-I (analog & digital) > VGA (analog).
Your TV picks the signal it wants, and since you have connected the cable to a VGA port on the TV it will need the analog signal, so that's what it will use. It will ignore the digital signal, no use for it here. No conversion needed! Just a DVI-I to VGA cable.
But here is another situation! Say your computer has only DVI-D (digital only) port on the back. Now you will need a converter.
- So it's like, DVI-D (digital) > ? > VGA (analog).
The question mark is where you would need some kind of converter that converts your digital signal into analog video signal, for you to be able to get the picture at the VGA end. For this situation there are "active" cables with a converter on them, or you can buy a DA converter separately, it looks like a little black box, and you connect your two types of cables to it, one at one end and the other at the other end.
So you really need to make sure you got the correct cable type. There are a lots of converter cables of this type in stores for people that want to connect their TV to the computer. Like you have seen in this example above, some people might be able to connect their TV to computer with a simple cable with two different connecters at each end, while others till would need a converter of some sort in-between.
Does your primary monitor have a HDMI port?
If so, then you can use a HDMI to HDMI cable to connect from your PC to your primary monitor.
If not, then I would suggest you connect your primary monitor with a HDMI to DVI-D (or DVI-I) cable. You can get one that has DVI-D or DVI-I at the other end, it doesn't matter, as the only signal that will be used is the digital signal when going from HDMI to a DVI device.
And then you can get simple DVI-I to VGA cable for your secondary monitor. No convertor is needed. For this to work your computer will have to support DVI-I. The integrated type that carries both digital and analog video signal.
So it would look something like this.
- Primary: PC (HDMI) > monitor (DVI-D/DVI-I)
- Secondary: PC (DVI-I) > monitor (VGA)
It's a very long answer, I know. But I really wanted to give you some bits of information so that you really understand the difference between these connector types and so that you can go out and pick the right cable and/or converter for your needs.
Just a small update on how you can check if your computer has DVI-I or DVI-D.
This is what the DVI ports can look like.
Don't worry about the dual and single link stuff, just take a look at it and see if it has those four holes at the left side that go around something that looks like a plus (or minus) in the middle. (It will look like a plus on the port itself. These are images of what the cable connectors will look like.)
The connector number two from the top (dual link, DVI-I) is the best kind that gives you the most advantages, like analog and digital signal and highest resolution (dual link). You could also go with the DVI-I single link, or the DVI-A which is very rare.