Why DisplayPort matters

HDMI , DVI, VGA, component, composite and S-Video - there's already a long list of display interface options. So, what's the point of the DisplayPort connector, yet another all-new interface that's beginning to appear on PCs, peripherals and components?

Whatever your needs, digital or analogue, open or encrypted, you might think there's an interface that already has you (and your PC) covered. What about HDMI? Isn't that the all-round digital connector of choice?

But 2008 is the year that DisplayPort is expected to come of age. The monstrous maker of PC kit that is Dell Computer is fully committed to the new interface and is already shipping compliant products.

But if there's little doubt DisplayPort is coming, the advantage it offers - particularly over HDMI - is less obvious. We therefore bring you our take on what DisplayPort will do for you and your monitor.

What is DisplayPort?

It's a royalty-free digital display interface standard overseen by VESA (that's the Video Electronics Standards Association) and designed specifically for use with PCs. VESA's intention is to deliver a unified replacement for VGA, DVI and LVDS, the latter being the internal interface used by most notebook PCs.

Physically, DisplayPort takes the form of a single 20-pin connector with a size and shape not dissimilar to HDMI. It's small enough, in other words, to cram four ports onto a typical graphics card bracket. Its size also makes it much easier to integrate on ultra portable notebook and pocket computing devices.

What's the point of DisplayPort?

DisplayPort's main aims are to: deliver more bandwidth, enable simpler connectivity and cabling, all the while keeping costs down. Here's how.

1. More bandwidth
In dual-link form, you might think DVI delivers all the bandwidth you could ever need. After all, surely 2,560 x 1,600 pixels is enough? Perhaps. But then it isn't just resolution that is limited by bandwidth - colour depth and refresh rates also come into the equation. Bump up either of those and you'll have to compromise on resolution.

Significantly, a new generation of high dynamic range displays is on the horizon. These are expected to push the current 24-bits-per pixel (bpp) colour fidelity of current displays up to as much as 48bpp. That means millions more colours and, in turn, more vibrant and realistic images.

It's also worth noting the increasing fashion for high refresh rates in the home cinema market. 120Hz is all the rage on TVs now. That's twice the refresh rate of digital PC monitors and requires twice the bandwidth at any given resolution. The latest HDMI 1.3 standard, incidentally, is essentially equivalent to dual-link DVI in video bandwidth terms.

Imagine, therefore, a 30-inch display with a resolution of 2,560 x 1,600 with 48bpp colour and 120Hz refresh rates and you'll get an idea of the enormous thirst for bandwidth that future displays will have.

The current DisplayPort 1.1 standard supports a maximum of 2,560 x 2048 pixels at 24bpp. Later this year, version 2.0 later arrives with 3840 x 2400 24bpp and the ability to seriously crank up the colour depth and refresh rates at lower resolutions.

2. Simpler cabling and connectivity
It's a jungle back there. We speak of course of the horrifying rats nest of cabling that can be found behind most PCs. But what if you could connect multiple displays and audio devices to your PC with just one cable? That's exactly what DisplayPort promises to do.

First up is optional support for a digital audio stream, just like HDMI. But that's just the beginning. Thanks to its packet-switched data format, DisplayPort will be capable of all kinds of devilry. For starters, daisy chaining multiple displays with a single cable to the PC will be possible. The existing 1.1 spec can handle three 1080p displays on a single cable. DisplayPort 2.0 will add support for even more displays as well as USB connectivity.


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