If they designed it to not have enough space for both cables to be connected at the same time, that must be their way of passively saying it doesn't work.I apologize ahead of time for those who are disinterested in 4K monitor support for the Surface Book, but I have further news to report here. Based on the article I linked in the above message, I went to the relatively extreme length of filing down one of my DisplayPort cables so that the mini-DP side had no plastic sheath, allowing it to fit (snugly) alongside the Surface Dock connector:
Unfortunately, this does not work on the Surface Book, which is a variation versus the Surface Pro 4. When the dock connector is connected, the base-connected monitor is powered off. It is powered on if the dock connector is disconnected.
So even with this approach, the Surface Book only powers a single 4K monitor at a time. Very disappointing.
That sure is the default reasonable point of view, especially if we give the designers the benefit of the doubt of not accidentally putting the port too close to the dock connector port. But multiple people had suggested the (remote) possibility that maybe a second 4K monitor could be powered if it were possible to connect one of the two monitors to the base, thereby only using one of the two connectors in the Surface Dock. Such a configuration would ostensibly avoid the dock's apparent inability to power two 4K monitors simultaneously.If they designed it to not have enough space for both cables to be connected at the same time, that must be their way of passively saying it doesn't work.
They certainly can't expect Surface Book owners to shave the cables to get them connected.
Displayport 1.2 link is limited to a single 4k monitor at 60 Hz. Driving Multiple Displays from a Single DisplayPort Output - DisplayPort
That is why the important point is how many links are coming out of the connector. If it is only a single DP 1.2 link, then it cannot drive two 4k at 60 Hz, period. If it is two DP 1.2 links then it should be able to drive both 4k at 60 Hz. But a Skylake only has three available video outputs. Assume one to the internal panel, one to the side port and one to the dock/power port and you have the three available video outputs. So that means while the dock may have two miniDP ports, their configuration is unclear but most likely there is an internal MST hub, which means a single DP 1.2 and thus only one 4k at 60 Hz.
You should try to run one 4k from the dock and one directly from the Book miniDP port. That is your best bet for getting to two 4k at 60 Hz, if they are indeed two different links from the Skylake. That is a much better chance than trying them from the dock alone.
On my SPro3, I had to connect the MST and the two 4k 30 Hz to the side miniDP port. The SPro3 dock port was too flaky.
I can say that I just tried with the newest available build of Windows 10, including all the appropriate drivers on any refresh rate (60/30) setting, and I am still unable to drive two external 4K monitors of any type. It doesn't matter if I use DP 2.2 or HDMI etc...Any update, protip? I don't have two 4k monitors now but I may one day and I'm curious to know if it's possible as well.
At work, every time I plug in my SB to the new dock I have to go through a 5 minute song and dance just to get it to work. I haven't been to work in a few weeks now and I'm hoping the drivers are updated before I go back but are you able to just use a single 4k monitor at 60hz just by connecting the dock? Does yours throw a fit as well?
On the Surface dock, no update. I have at this point given up on attempting to drive two 4K monitors at 60 Hz with the Surface Book + dock. I believe it's simply not possible given these pieces of hardware. There have been some creative workarounds suggested elsewhere such as using a USB display adapter, but I have not tried that.Any update, protip? I don't have two 4k monitors now but I may one day and I'm curious to know if it's possible as well.