There are different types of DVI ports: the analog-only DVI-A ... So you'll need a VGA adapter to connect a modern computer to a monitor that only has VGA. However, it's well worth it since ...
The HDMI interface is electrically identical and compatible with the video-only DVI interface, which came first. For example, if a cable box or PC has DVI out, but the TV or monitor only has HDMI ...