Technical differences between HDMI and DisplayPort?


Djhg2000

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So both of them can connect with each other with passive adapters (HDMI -> DP or DP -> HDMI), both are (as far as I understand) based on DVI-D and they both carry audio. Yet they supposedly use incompatible signaling schemes. Does this mean all hardware capable of DP must also be able to deal with HDMI? I understand this is determined by the EDID which is fine since that just lives in a flash chip on the I2C bus. But what if you forced an HDMI signal on a DP bus? How hard would it break? Furthermore, does this mean there's a secret HDMI licensing fee baked into the DP standard? If someone could explain all this in detail it would be greatly appreciated.
 
Imagine I write a program that can display gif images. That's all it does. I charge $1 for this program.  People pay this because it is really good at what it does and there aren't really any other choices; almost every single image out there is a gif.
You come along and write a program that can display jpeg images. That's all it does. You do this so that no one needs to pay royalties for my gif image viewer.  There aren't as many jpeg images as there are gif, but a few people use it.  Someone writes a "gif to jpeg" converter which means people can convert their image and display it in your viewer, but it's an extra step, and a little bit of quality is lost in the conversion.  Similarly someone makes a jpeg to gif converter but because almost everything is gif anyway it doesn't get a lot of use.
Eventually you come up with a jpegviewer++. It is the exact same jpeg viewer that you wrote before but now, if someone tries to use it to read gif images, it bypasses its own jpeg renderer and just loads up my program in the background in order to display the image.
That's effectively HDMI vs DisplayPort.  They are different, incompatible standards.  In order to use one with the other you need an active conversion cable to change the signal from one to the other.  DisplayPort++ can use a passive HDMI converter because, when you plug in the cable, it stops pushing DisplayPort data and redirects some of the pins to an HDMI controller.  A DisplayPort++ has both a DisplayPort controller and an HDMI controller in it, that's why it can do both.
 
Imagine I write a program that can display gif images. That's all it does. I charge $1 for this program.  People pay this because it is really good at what it does and there aren't really any other choices; almost every single image out there is a gif.
You come along and write a program that can display jpeg images. That's all it does. You do this so that no one needs to pay royalties for my gif image viewer.  There aren't as many jpeg images as there are gif, but a few people use it.  Someone writes a "gif to jpeg" converter which means people can convert their image and display it in your viewer, but it's an extra step, and a little bit of quality is lost in the conversion.  Similarly someone makes a jpeg to gif converter but because almost everything is gif anyway it doesn't get a lot of use.
Eventually you come up with a jpegviewer++. It is the exact same jpeg viewer that you wrote before but now, if someone tries to use it to read gif images, it bypasses its own jpeg renderer and just loads up my program in the background in order to display the image.
That's effectively HDMI vs DisplayPort.  They are different, incompatible standards.  In order to use one with the other you need an active conversion cable to change the signal from one to the other.  DisplayPort++ can use a passive HDMI converter because, when you plug in the cable, it stops pushing DisplayPort data and redirects some of the pins to an HDMI controller.  A DisplayPort++ has both a DisplayPort controller and an HDMI controller in it, that's why it can do both.

Thanks, this is a really good explanation. I think I get it now.
 
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