They’re all sending digital information, but only data cables like USB/Thunderbolt can be used (as far as I know) for devices like external drives. I am not aware of any external drive that can be connected by HDMI or DisplayPort.
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There really is not much difference from an electronic point of view. Both send millions of bits of digital information over the cable. In HDMI it’s used to form a moving picture with audio, in USB it can do that plus it can also transmit information like digital files, etc. There are differences in how the data is formatted; HDMI sends uncompressed image and audio data constantly at a more or less unchanging rate, whereas USB is more flexible and can do that or just send chunks of data as needed. HDMI is probably also rated for higher bandwidth than USB. In theory there is no reason why there couldn’t be one cable to rule them all, but HDMI was developed when USB was too slow for HD video, and even though USB has caught up, it’s not worth the hassle of changing over again.
The core differences are not that huge, other than the actual utility of the 2 protocols:
* Regular HDMI is rated around 20gbit/sec in data throughput over 3 channels (all out 1 way)
* USB-C is rated about 20 gbit/sec over 2 channels (in/out bidirectional).
* USB can provide power to devices, like flash storage (thumb drives etc)
* HDMI can go about 50 feet before signal loss, USB usually about 25 feet
I didn’t compare Thunderbolt but you could look that up and compare.
As you said it’s just data, but USB formats already support storage I/O already pretty well so why would someone build an HDMI input device?
Surprisingly almost nothing at all
Both sets of cables send data over high speed twisted differential pairs (one wire goes high when the other goes low, then they flip which one is high)
The difference is that we setup the protocol and controllers for HDMI and Display Port to talk to a display from a source, while USB and Thunderbolt are setup so that two equivalent devices (or one superior and one lesser device) can talk to each other
The most obvious example of this is Thunderbolt and DisplayPort. Thunderbolt uses a Mini Display Port connector, but a Thunderbolt enabled host talks to whatever it got plugged into to determine if it will be sending data to the other device using the Thunderbolt protocol or if it will be sending video to a display using the DisplayPort protocols
Electrically the signals are the same, it just sends different signals depending on how the device on the other end is expecting data to come in
Aww, really? Nothing? I’m going to guess and say the data is like comparing apples and oranges.
If you speak to me in Russian, that’s still speech, but I’m not going to understand it. I’d have to learn Russian first.
If you teach me the language of some isolated tribe that’s never seen a car, then want to use that language to discuss the details of how to rebuild your car engine, it’s not going to work. That language just doesn’t have the vocabulary to describe the concepts. (You could try to add extra words, but then you’re speaking a new language, and you’d have to teach both people involved that new language).
USB, Thunderbolt, HDMI and DisplayPort are all languages. Only USB and Thunderbolt have the vocabulary to allow a hard disk to communicate with the PC. HDMI and DisplayPort are specialised languages designed to let a source of video data talk to a display.
The quick answer is that different devices have different needs, so it was easier to make a specific cable for every need. For example a monitor requires a very high speed data transfer, a usb device needs both data and power, a mouse doesn’t need a lot of data but it requires a low delay to be useful.
On top of that, the different ports were developed by different companies and each of them thinks that their format is the best. So they make their port incompatible with the others or ask for huge fees to use their format.
Now that there is a stronger push for standardization between formats, the usb-c can handle displays, hard disk, and almost any device that needs to exchange data and companies are starting to adopt it. (Except apple?)
The part about about the device needs still remains: you have only one shape of port but you need different cables depending on what you want. For example: some usb-c cables support power delivery and some others not.
Even usb-c ports are different. On laptop is common to have a usb-c port that only supports charging, one that supports a video stream, one that supports normal devices…
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