Basic video cabling for computer users

What *are* all these connectors?

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Programmers often want to connect computers to display units other than those used in normal operations. Reasons include:

  • projection on a screen for group work in a meeting, conference, exhibition, sales presentation, or so on;
  • extra pixels for hard work: programmers are demonstrably more productive the more addressable real estate they can manage;
  • "converged media" episodes, where you feed 'Net or computing content (TED talks, favorite scenes from M*A*S*H, last week's telenovela) to an "entertainment center".

My preferred approach to these situations is to push whatever content I have to the Web, and use a dedicated display-browser hardware installation that has already been shaken down, to retrieve the content. Most sites don't offer such a set-up, though; they assume we'll hook our own machines to their projectors or other displays.

Will this involve wires?

Yes. While plenty of possible futures involve wireless negotiation between the different devices, those technologies remain at the hobbyist level for now. When someone asks you to show your latest PowerPoint marvel to his group, what he effectively means is that you'll tote along a laptop you control, and connect it (possibly through a converter you know to bring with you) to one of several wires emerging from his projector rig. While this basic picture has changed little for at least fifteen years, and most of the standards involved are at least that old, the rise of digital television has at least shifted the landscape a bit. Let's look at the facts:

Common wires

While over a dozen different connectors have been used on popular computers for video output at one time or another, contemporary units, including laptops and netbooks, mostly offer at least one of:

  • VGA (mostly transporting SVGA signals),
  • composite video ,
  • S-Video ,
  • DVI ,
  • HDMI , and
  • DisplayPort

Projector installations nearly always accept at least two different formats, with at least one, like S-Video, prominent in consumer electronics, as opposed to computing. If in doubt about what you're facing, ask; often as not, the answer will come back, "I don't know; it just plugs in to your laptop", or something similarly unhelpful. In most common situations, you can assume VGA will be available.

I like to carry converters between some of the other connectors (DVI-A to VGA or S-Video to VGA or S-Video to composite, for example). It's fairly easy to cover most common situations, and prohibitively clumsy and expensive to be ready for them all.

There's plenty of advice available on-line and in books about which connections are the most desirable; much of this counsel is flawed in that it poorly accounts for real-world situations. In principle, digital connections are more robust than analogue, and I'm happy to use digital protocols when available. For the most part, though, the most important milestone is simply to get some connection working properly. This is more challenging than might first appear, because, even in 2010, standardization of controls for display switching remains poor, and low-quality or damaged cables often lead to erratic results. Concentrate on establishment of a connection that allows your audience to see adequately; invest in re-engineering that connection to higher fidelity and performance only if you have time to spare.

The principles of use of an external display have changed little in the last couple of decades; the details which actually make it possible keep adjusting, though, and are hard to document in any comprehensive way. TechLore published a help page on projecting from a Dell laptop just two years ago. eHow ran an even more basic introduction to the topic a bit earlier. For more details and the latest news on these subjects, I recommend "Alfred Poor's HDTV Resource Center" and "Videotcy". Also, my thanks to the Wikimedia Commons, which provides the images of specific connectors shown above.

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