Data projectors usually accept a variety of different signals. They nearly always feature a VGA port (analog RGB signal) but more up-to-date are DVI or HDMI ports (digital RGB signal), which can nowadays be found with all graphics cards and notebooks. Due to the fact that no digital-analog-digital conversion is necessary, these types of port offer better quality. A further advantage of DVI and HDMI is communication between the devices. Via the EDID (Extended Display Identification Data) the graphics card dialog automatically offers the resolutions supported by the video projector. Standard DVI cables are limited to 3 m in length. Longer distances of up to 20 m should be covered by high-quality copper cables. Any distances beyond this require special solutions, e.g. repeaters for refreshing the signal or DVI-CAT5-DVI extenders, which allow up to 60 m for WUXGA via a standard low-price network cable, or fiber optic cables which can bridge up to several hundreds of meters.
For the new generation of HDTV units HDMI ports were introduced. Image transfer is compatible with DVI, but HDMI can additionally transfer audio. HDMI connectors are very compact but they cannot be screwed down like DVI. There are HDMI to DVI adapters and vice versa, allowing both types of cables to be combined. Those who want to digitally transmit HD DVDS to a projector in the future should also make sure that HDCP standard for secure encryption and copyright protection is supported. Otherwise the player may refuse digital playback.
Even today DVI and HDMI are still very useful standard interfaces. Along with higher resolutions, however, came new standards: HDMI 2.0 and Display Port 1.2. With HDMI 2.0 special focus must be placed on what the corresponding device can handle as the manufacturers are not forced to support all features of HDMI 2.0. Display Ports 1.2 will put you on the safe side for 4k applications but are unlikely to be found with home cinema projectors as they are too expensive. The decisive factor is the resolution you want to use for your presentation:
DVI Single Link 
1920 x 1200 pixels with up to 60 Hz
DVI Dual Link 2560 x 1600 pixels with up to 60 Hz
HDMI 1.2 1920 x 1200 pixels with up to 60 Hz
HDMI 1.4 1920 x 1200 pixels with up to 60 Hz and 4096 x 2160 pixels with up to 30 Hz, UHD (3840 x 2160 pixels) and up only with croma subsampling 4.2.0 instead of 4.4.4
HDMI 2.0 4096 x 2160 pixels with up to 60 Hz, UHD (3840 x 2160 pixels) and up only with croma subsampling 4.2.0
Display Port 1.2 4096 x 2560 pixels with up to 60 Hz
For fluent motion in videos the video signal refresh rate must be matched with the video frame rate. I.e. for a video with 25 or 50 f/s the video projector should be able to play smoothly at 50 Hz.
Analog VGA cables are nearly extinct and make no sense with XGA resolution. Up to 30 m are relatively easy to be covered by a high-quality, low-attenuation cable. The loss depends on length and quality of the cable, but also on the resolution used. The higher the resolution, the more emphasis must be placed on this. A DVI-I port (I = integrated) additionally offers a VGA connection via an adapter.
Other video ports, such as component or S-VHS ports do not play a role in presenting high-end videos as they use interlaced, low-resolution TV signals. Also audio inputs for integrated loudspeakers are of little importance. They do not offer the high quality required for professional presentations. Network and USB ports for mouse control and projector configuration via computer may also be quite useful.
See also