Many computer monitors feature multiple types of connections. These ports vary depending on the type, sophistication and age of your specific monitor. Your hardware and its input/output options determine the cabling you need to make your computing activity visible on your display. If your system offers more than one connection option, these display protocols' features and advantages can help you choose which type of cable to use.
Common on CRT monitors and older LCD monitors, Video Graphics Array, or VGA, delivers an analog video signal over a 15-pin cable. LCD monitors convert analog signals to digital for display purposes, which can introduce noise and artifacts into the onscreen signal you see. The original VGA specification only supported resolutions up to 640 by 480 pixels. Other forms of VGA include XGA, WXGA, WSXGA and WQXGA. WQXGA uses a standard VGA cable to display a resolution of 2,560 by 1,600.
Digital Video Interface, or DVI, provides one of the most common forms of digital connections for monitors. DVI cables use up to 24 pins for a digital signal and an additional four pins for an analog signal. The DVI specification includes DVI Single Link and DVI Dual Link. Released in 1999, DVI Dual Link can support resolutions up to 2,560 by 1,600 pixels. Because DVI uses a digital signal, it avoids the digital artifacts and noise commonly produced with VGA cables.
High-Definition Multimedia Interface, or HDMI, provides the standard for digital connections to LCD TVs and other home theater equipment, and has gained popularity in the computer industry. Newer monitors and video cards often incorporate HDMI interface options. HDMI cables deliver the same resolution as DVI cables, but HDMI cables also carry digital audio on the same connection. Compared to DVI cabling, HDMI uses much smaller connectors with only 19 pins.
DisplayPort and Mini DisplayPort
Although DisplayPort lacks the popularity of HDMI and DVI, its digital connection carries the same resolution. Look for DisplayPort as a feature on Apple products, including the iMac, MacBook Pro and Mac Mini. Few monitor manufacturers support DisplayPort's 20-pin interface on their products because of its limited market penetration. To convert a DisplayPort signal into the DVI or HDMI standards more commonly available on computer monitors, look for an adapter to use with either DVI or HDMI cables.
The limited bandwidth of USB 2.0 cables imposes an equivalent limit -- 1,024 by 768 pixels -- on the display resolution of USB-connected monitors, but this protocol can support a secondary display using a standard data cable. The offsetting advantage of its comparatively low resolution lies in USB's ability to provide a video signal without the need for a monitor port, underlying its ideal use to connect a subsidiary display.