A classic DVI-I connector.
DVI stands for “digital visual interface”.
Contains more pins that DVI-D.
Can send analog and digital signal to your monitor.
Can work with old CRT monitors and new LCD/LED monitors.
Contains less pins than DVI-I.
Can send only digital signal to your monitor.
Can only work with new LCD/LED monitors. However, there are adapters that can make a conversion like this: DVI-D to VGA (the blue jacks) and you will be able to connect your video card to an old CRT monitor.
If you want to buy a new monitor, make sure you can connect your video card to it. If the monitor has HDMI and DVI-I, your video card should have either a HDMI or a DVI-I jack.
Most of the new monitors come with the HDMI technology and if you own a video card that is not ancient, it should have HDMI and you will be able to connect it to your new monitor.