It was so easy when PCs could connect to their CRT (cathode ray tube) monitor with a single 15-pin mini d-sub connector, also known as the VGA (video graphics array) plug. The VGA plug connected to the graphics card in the PC. The graphics card translated the PC�s digital information into an analogue signal and transmitted it to the monitor which displayed a digital image of the information. The term d-sub refers to the shape of the plug itself (a �D�) and are often called DB connectors. They come in 9, 15, 25, 37 and 50-pin sizes. The D-sub connector defines the physical structure of the connector, not the purpose of each line. There were no options. That was it.

That was then. Today, most LCD (liquid crystal display) monitors can display digital data direct from the CPU. The digital signal can be sent from the CPU to the LCD monitor via a DVI (digital video interface) connection. However, many computers still have analogue video cards that support VGA connectors, which means that many LCD monitors have two video inputs, the VGA input and the DVI input. Graphic cards similarly have the dual capabilities.

But it�s not quite that simple. There are three different formats of DVI: DVI-Digital, DVI-Analogue, and DVI-Integrated (Digital & Analogue)

DVI-D - True Digital Video
DVI-D cables are used for direct digital connections between source video (namely, video cards) and digital LCD (or rare CRT) monitors. This provides a faster, higher-quality image than with analogue, due to the nature of the digital format. All video cards initially produce a digital video signal, which is converted into analogue at the VGA output. The analogue signal travels to the monitor and is re-converted back into a digital signal. DVI-D eliminates the analogue conversion process and improves the connection between source and display.

DVI-A - High-Resolution Analogue
DVI-A cables are used to carry a DVI signal to an analogue display, such as a CRT monitor or an HDTV. Although some signal quality is lost from the digital to analogue conversion, it still transmits a higher quality picture than standard VGA.

DVI-I - The Best of Both Worlds
DVI-I cables are integrated cables which are capable of transmitting either a digital-to-digital signal or an analogue-to-analogue signal. This makes it a more versatile cable, being usable in either digital or analogue situations. Like any other format, DVI digital and analogue formats are non-interchangeable. This means that a DVI-D cable will not work on an analogue system, nor a DVI-A on a digital system. To connect an analogue source to a digital display, you'll need a VGA to DVI-D electronic converter; to connect a digital output to an analogue monitor, you'll need to use a DVI-D to VGA converter.

Most LCD monitors, then, have options for both VGA and DVI inputs. That�s fine if you only want to connect your LCD display to your PC. But what if you want to use your LCD as a TV or display for your DVD player? Then you need more inputs.

Multimedia Inputs
Some multi-media LCD monitors have what is known as an S-Video (separate video) input. S-Video is round (DIN) style cable connector/port used to digitally transmit video signal. It is commonly found on some higher end television monitors, DVD players, satellite receivers and video editing cards. It is also becoming more common on some of the larger LCD monitors so that they can be used for DVDs or TV.

Many high-end LCD displays also have BNC video inputs. BNC stands for the Bayonet-Neil-Concelman connector and it is the most popular connector in CCTV and broadcast TV for transmitting a basic bandwidth video signal over a coaxial cable. This gives you even more options for your LCD display.

What�s Next: HDMI
All these connectors are fine, but pretty soon we�re going to be seeing TV, DVD, internet video and every other type of multi-media from multiple sources through your PC-based monitor. This will overwhelm the capabilities of your basic DVI and other associated interfaces.

The DVI standard was, for a short while, the digital transfer method of choice for HDTV (high definition TV), plasma display and other ultra-high-end video displays for TV, movies and DVDs. Likewise, even a few top-end DVD players have featured DVI outputs in addition to the high-quality analogue Component Video. The digital market is now swinging towards the HDMI interface for high-definition media delivery.

HDMI (High Definition Multimedia Interface) is an all-in-one, standardised, universal connector for audio/video applications. Featuring a modern design and backed by the biggest names in the electronic industry, HDMI can unify all digital media components with a single cable, remote, and interface. HDMI is built with a 5 Gbps bandwidth limit, over twice that of HDTV (which runs at 2.2 Gbps), and is built forwards-compatible by offering unallocated pipeline for future technologies. The connectors are sliding contact (like FireWire and USB) instead of screw-on (like DVI), and are not nearly as bulky as most current video interfaces

The high bandwidth of HDMI is structured around delivering the highest-quality digital video and audio throughout your entertainment centre. Capable of all international frequencies and resolutions, the HDMI cable will replace all analogue signals (i.e. S-Video), as well as HDTV digital signals (i.e. DVI), with absolutely no compromise in quality. Additionally, HDMI is capable of carrying up to 8 channels of digital-audio, replacing the old analogue connections.

HDMI 1.3, the latest standard, further increases the bandwith limit to 10.2 Gbps, to allow for the video and audio improvements of the upgraded standard. HDMI 1.3 uses a smaller connector than the original HDMI connector. They are both similar in appearance, but the HDMI 1.3 plug measures about half the size.

What�s Next After HDMI? UDI
But that is still not fast enough! Unified Display Interface (UDI) is a proposed improved digital video interface specification based on the existing DVI interface. It is intended to be a lower-cost implementation while providing compatibility with existing HDMI and DVI displays. It provides higher bandwidth than previous digital ports (up to 16 Gb/s in its first version compared to 5 Gb/s for HDMI) and includes a form of Digital Rights Management (DRM) known as HDCP.

UDI is specifically targeted towards the needs of computer monitor and video card manufacturers, as opposed to HDMI which is aimed at high-definition multimedia consumer electronics devices such as television monitors and DVD players.

In December 2005, the UDI Special Interest Group (UDI SIG) was announced. They will work on determining the refined specifications and promoting the interface. Members include Silicon Image Inc., Intel, Apple Computer, LG, Samsung and NVIDIA.

The final specification is expected to be finalised by the end of 2006. The differences between UDI and HDMI will be kept to a minimum, as both specifications will be aligned for long-term compatibility.

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