A DVI to VGA connection transfers a signal from the digital DVI source to the analogue VGA device. This can be done through a DVI to VGA cable or via an adapter.
A DVI to VGA adapter is used to connect a VGA/SVGA monitor or TV to a DVI-I connection, like on a laptop. However, as the VGA signal is analogue the correct DVI counterpart is needed for it to work.
VGA, or Video Graphics Array is a popular, but slightly dated, connection format. VGA cables carry an analogue signal as opposed to the digital signal you’d find in HDMI or DVI.
Because of its once widespread popularity VGA is found on a large proportion of older TVs as well as most monitors. Because it is an analogue format VGA only monitors sometimes struggle linking to laptops or tablets which tend to have digital connections.
DVI (Digital Visual Interface) is a digital video connection. It is effectively an upgraded version of VGA to carry the more common digital signal.
DVI comes in a few flavours with DVI-D (Digital), DVI- A (Analogue) and the most popular DVI-I – This is essentially a combination of DVI-D and DVI-A cables within one cable, which as you can imagine is far more useful when connecting to multiple devices.
Check here for a more detailed guide on cable formats.
What to use
So if you’re connecting your VGA monitor to a PC or Laptop what do you need?
If your display has a VGA connection, and the PC/laptop is DVI connection, you should use a DVI-I (DVI-A) to VGA cable or adapter. From this, your resulting connection will be in analogue format, meaning your monitor or TV can understand the signal. DVI-I to VGA effectively works as a standard analogue VGA connection bypassing the digital element meaning the connection is more like DVI-A to VGA.