I have an i-tec USB 3.0 4K Ultra HD Display Adapter - Display Port from which uses a display-link driver.

However, this setup uses a huge amount of processor power as it emulates a graphic card.

I now have a Surface Go which has a USB-C port. Some graphic adapters use USB-C instead of USB 3.0 and they are much cheaper as my older USB 3.0 device (was About 80€).

As the Surface Go has a very low-end CPU I am wondering if these USB-C solutions also consumes much CPU power in emulating a graphic card or does USB-C works completely different?

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    Yes; It will due to the fact your processor is performing all the work no matter what the connection is. – Ramhound Oct 11 '18 at 15:25
  • @Ramhound - not necessarily... see my answer. "it all depends" – Attie Oct 11 '18 at 20:36

Talking generically for a moment...

The truthful answer is - it depends.

USB-C is becoming quite a difficult connector to deal with - the physical interface is also commonly used for other things, by supporting what are called "Alternate Modes".

In addition to the alternate modes, is the "Power Delivery" mess, where one device can provide power to another device at "up to 20V at 5A"... Thus we already have a situation where a laptop charger will work for a phone, but a phone charger won't work for a laptop.

A quote from the USB-C wiki page:

A device that implements USB-C does not necessarily implement USB 3.1, USB Power Delivery, or Alternate Mode.

These things are fine if you know about them, you're technically minded and able to understand / clearly communicate what's going on... however... this isn't always true of consumers or retailers (as you'll see below).

As of today, the Alternate Mode options include:

So... by purchasing a dongle that physically appears to be "USB-C to DisplayPort", there are some possibilities as to what this may actually implement: (this is a similar story for HDMI).

  1. USB 2.0 → DisplayPort (unlikely but possible)
  2. USB 3.x → DisplayPort
  3. DisplayPort
  4. Thunderbolt → eGPU → DisplayPort

Options 1 and 2 will quite possibly be either a DisplayLink adapter like you already have (CPU-intensive), or some other adapter (also CPU-intensive, possibly moreso). Your computer should support this without problems, though performance is likely to be an issue.

Option 3 is great - it'll be a (nearly) passive cable which connects your computer's internal graphics to an external monitor. Small, cheap, simple. No additional load on your CPU when compared to a standard DisplayPort monitor. Your computer (or some of the available ports) may not support this.

Option 4 is also great - it'll likely require external power (think eGPU), will be a large box, and will essentially connect a PCIe graphics card to your computer via Thunderbolt. Large, but potentially very powerful (i.e: gaming, CAD, etc...). Your computer (or some of the available ports) may not support this.

Talking specifically about the Microsoft Surface Go...

Sadly Microsoft have fallen directly into the hole, and have specified "1× USB-C" on the tech specs page - great... what does that mean?

There is a "Surface USB-C to DisplayPort Adapter", but it doesn't mention anything about what this (sizeable looking) dongle actually implements, and it doesn't even have an "I'm compatible with" list.

I'm afraid after a bit of a look around I'm not able to give you a definitive answer to your core question - I'm not even able to give you advice to help you avoid the CPU-intensive options, because I can't find out what the Surface Go's USB-C port actually implements!

The best I can do is suggest you try the Microsoft adapter... or another adapter, looking out for "DisplayPort Alternate Mode" phrasing. If that doesn't work, then you'll be stuck with option 1 or 2 from above (i.e: DisplayLink).

  • Wow many thanks for your very detailed answer. I bought the much too expensive MS Dongle today and will test it. Would be great if MS would have been more precise about their techs... – SRel Oct 11 '18 at 21:00
  • Yeah... I asked on twitter, and got a completely off topic response... – Attie Oct 11 '18 at 21:46
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    Apparently the Microsoft marketing has decided that all this gobbledygook about alternate modes over Type-C is above comprehension of general public, so they even skip on training of their own support personnel, and just give you an "adapter" to plain DP cable. – Ale..chenski Oct 13 '18 at 4:14

From the teardown review of Surface Go on iFixit, the Type-C port is driven by Parade Technologies "USB-C Host Switch with PD 2.0 Controller and USB 3.1 Gen 1 / DP Alt Mode HBR2 Redriver" PS8743x chip, which is designed to support DP alternate mode. It would be very odd if Microsoft wouldn't use this specific functionality, which likely comes with additional IC cost.

Therefore, your Surface Go is likely to support direct connect to DisplayPort, and thus uses the internal dedicated Intel® HD Graphics 615 processor, and not the virtual display over USB as DisplayLink video uses. I would guess that 615 graphics is less CPU intensive and faster than the DisplayLink over USB.

However, the switch to alternate mode does require some Power Delivery communication. If you happen to have a DP display with Type-C input, you probably will be fine with a standard full-featured Type-C to Type-C cable, directly without any adapter. The DP display should provide all necessary handshake on CC wires across the C-C cable. But if you have a DP display with native DP input, a simple cable won't have the necessary communication means (the PD structured VMs), so the Microsoft provides this special extra dongle (adapter), which does the PD communication, so you can use an ordinary DP-DP cable.

  • Nice catch - I didn't even think to look for a teardown. – Attie Oct 13 '18 at 10:22

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