Tom dives into the history of DisplayPort and explains why DisplayPort isn’t just HDMI with a new-fangled connector.
Featuring Tom Merritt.
Episodes mentioned:
About USB 4
About Variable Refresh Rate
About HDMI 2.1
MP3
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Episode transcript:
A buddy of mine gave me a monitor and it uses DisplayPort? What the heck is that?
I looked it up and the connector looks like Thunderbolt AND USB-C. What the heck is up with that?
And what is it good for anyway? Why isn’t it just HDMI?
Confused? Don’t be. Let’s help you Know a Little More about DisplayPort.
DisplayPort is one of many different interfaces that turn bits of data into pictures on a monitor for you. It’s the one that has that rectangular connector with a funny angle on one corner.
DisplayPort is developed by the Video Electronics Standards Association or VESA. VESA is a standards incorporation created by NEC Home Electronics in July 1989 as a successor to the VGA standards. The organization now made up of about 300 companies and is based in San Jose, California.
OK back to DisplayPort.
DisplayPort is a high-quality display tech. It has something called Dual mode that can output either DisplayPort, Single-link DVI or HDMI from the same port. I know. That’s more than two. But it’s still called dual mode. Deal with it.
Because of dual mode, DisplayPort is compatible with HDMI and single-link DVI with passive adapters. Just dongles. If you want more, like dual-link DVI, you’ll need a powered active adapter. But I know you only care about HDMI. You can use a passive adapter to use a DisplayPort jack with an HDMI display. But you can’t connect DisplayPort to an HDMI source. Well, technically, it can be done but it’s not practical. So if your laptop has a DisplayPort jack and your monitor is HDMI you can get a dongle. If your laptop has an HDMI port and your monitor only has DisplayPort, that’s probably not going to work.
Now I know that most of you identify a display connection by the connector. The shape of the plug.
DisplayPort supports two types of connectors. A full-size connector, the previously mentioned one with the angled corner. That one is called Standard DisplayPort. It sometimes comes with a latching mechanism.
The second type is a mini display port connector, which was developed by Apple and logically called Mini DisplayPort. Thunderbolt 1 and 2 used the Mini DisplayPort connector shape before Thunderbolt switched to USB-C’s shape for Thunderbolt 3.
There are a few other types of DisplayPort connections you may encounter.
An embedded DisplayPort connection or eDP is used in some laptops to connect the motherboard to the screen. That all happens inside your laptop so you’ll probably only run into it during repairs. And inside TVs there is a version called Internal Display Port or IDP. Again. All on the inside.
One you’re much more likely to come across is DisplayPort’s Alt Mode on USB-4. This lets DisplayPort signals come out of a USB-C port. You can do this because some of the pins on the USB-C connector are reserved for other protocols. Like DisplayPort. DisplayPort is part of the USB4 standard. (See our episode on USB4!) So you can connect a laptop with a USB-C port to a DisplayPort monitor! Yay!
So what does the DisplayPort protocol itself do?
DisplayPort has 4 lanes of data and can transmit video and audio either simultaneously or one without the other. It can also carry USB 2.0 data. It supports up to 32 channels of 16 or 24-bit audio. Because it has independent data streams it can support multiple monitors– if it has enough bandwidth for the resolution.
A note about bandwidth numbers. You’re going to hear two kinds of bandwidth specs in this episode. The DisplayPort spec notes both. Maximum bandwidth is how much the standard is capable of. Effective bandwidth is how much you get after accounting for the overhead of encoding.
VESA approved DisplayPort version 1.0 on May 3 2006. It allowed a maximum bandwidth of up to 10.8 gigabits per second. Version 1.1 added support for HDCP and fiber optics, meaning cables could be longer.
In January 2010, Version 1.2 doubled the maximum bandwidth to 21.6 Gbps. It added Multi-stream Transport, or MST so you can daisy-chain multiple monitors on one port. It officially included Apple’s Mini Display Port as well. That’s the one that shared a connector shape with Thunderbolt before Thunderbolt changed its connector shape to be the same as USB-C. Sigh.
In January 2013, version 1.3 added optional support for adaptive sync like AMD’s FreeSync. We covered that a little in the episode on Variable Refresh Rate.
On September 15 2014 brought out DisplayPort 1.3 with a maximum bandwidth of 32.4 gigabits per second with HBR3 mode that featured 8.1 Gb/s per lane. The effective bandwidth was 25.92 Gb/s. That gave enough overhead to support 4K at 120 Hertz, two 4K monitors at 60 Hertz, or even 8K at 30 Hertz. It also added support for HDMI 2.0 (see our episode on that as well) and HDCP 2.2 copy protection.
In March 2016, Version 1.4 didn’t increase bandwidth, but it did add support for HDR10 metadata, Forward Error Correction and a big one, Display Stream Compression aka DSC. DSC helps squeeze more bandwidth out of video signals. It really accounts for a lot of what DisplayPort can do now. But it does modify the signal a bit. They call it a “light compression.” In practice it affects video quality more than latency since it encodes and decodes in real time, but it doesn’t affect either very much. Version 1.4 also increased the maximum in-line audio channels to 32.
Finally, DisplayPort 2.0 came along June 26 2019. It has a maximum bandwidth of 80 Gbps. and supports 8K at 60 Hertz without compression. With DSC it can go all the way up to 16K at 60Hertz or two 8K displays at 120 Hertz and even three 10K displays at 60 Hertz. Oh, I know. None of you have 8K monitors. Fine. For someone who would like a more practical example, try two 4K monitors at 144 Hertz with no compression or three 4K at 90 Hertz.
If you’re using USB-C to connect to a display-port monitor, Display Port Alt Mode 2.0 can support one 8K monitor at 30 Hertz with no compression or 2 4K monitors at 120 Hertz and 3 4K monitors at 144 Hertz with compression.
Another thing it can do with all that adaptability is support VR and AR headsets at high resolution since headsets have one screen for each eye.
OK. Now you know what the DisplayPort can do, let’s talk cables!
There are three certifications for DisplayPort cables and 5 names for the speed of the cable. The speeds I’ll give here are the effective speeds, aka the speeds you get after accounting for overhead. When shopping you may see either the speed name or the certification type, so I’ll give you both.
RBR (both the name for the certifications and the speed) supports version 1.0 up to 6.48 Gb/s. You probably won’t see this one anymore.
Standard certification supports version 1.2. That covers the HBR and HBR 2 speeds of 10.8 Gbps and 17.28 Gbps.
And DP8K certification supports versions 1.3, 1.4 and 2 and the HBR3 and UHBR speeds of 25.92 Gbps and 77.36 Gbps.
Cables can run from from 2 meters to 15 meters long. Though if you’re daisy-chaining that will reduce the maximum length it works at.
If you don’t know what version your device supports… good luck? One annoying thing about DisplayPort is you usually have to look at spec sheets to tell the version. There’s no standard way of identifying it on ports or cables.
And another annoying thing is Deep Sleep. This is an energy-saving mode on some DisplayPort monitors that doesn’t cut power entirely when they go to sleep in order to wake faster. Great when it works. If you’re having trouble getting your DisplayPort monitor to wake from sleep, disabling deep sleep may help.
So who is DisplayPort for? If you’re not trying to get the cheapest option and you don’t need the widespread compatibility of an HDMI, DisplayPort will give you higher refresh rates and more options to configure adaptive refresh rates.
In other words, I hope you know a little more about DisplayPort.
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