Technically 4k/60 Hz support has nothing to do with Broadwell.
Haswell can drive the full 4k resolution @ 60 Hz just fine (I have tested Surface Pro 3 here, Haswell and Intel HD5000).
For whatever wanky reason, it was solely Apple's decision to limit 4k resolutions at 30 Hz on Haswell MacBook Air artificially.
In order to force people, who wanted 4k/60Hz, buying more expensive MBP's, I guess...
It's the GPU onboard the CPU.
Are you sure it was 60Hz?
Why is everyone having so much problem with 4K monitors + SP3 at this subreddit then:
https://www.reddit.com/r/Surface/comments/2916ge/surface_pro_3_4k_support/
Note that some monitors are hacking in the 4K support via MST but it is still 30Hz.
Which monitor and which port are you using?
I'll be the first to admit I really don't know a lot about the technicals of computers and electronics, but I thought Type-C was based on USB 3.1 and capable of 10Gbps. Still not enough to drive 5k, but still better than 3.0.
No, USB Type C is not the same thing as USB 3.1, they're two separate things. You can have a data pipe inside Type C to carry the data (USB 3.0/USB 3.1), while also using video pipe (currently limited to DisplayPort 1.2 spec) inside to carry the video and finally, the power spec for charging as it can use up to 100W to charge.
USB Type C is more about the connector/pipe spec than more about the speed, basically how to carry multiple different data/video streams plus power for charging in one cable. You can upgrade the internal video/data specs and still use the same USB Type C connector.
The video standard support inside the USB Type C that Apple is using is set to DisplayPort 1.2a speed, which means it cannot support more than 4K@60Hz. In the future hardware, as support comes in, you can have the same USB Type C connector with support for USB 4.0 speed and DisplayPort 2 or whatever they call.
That's not how it works.
http://www.slashgear.com/look-out-t...-and-displayport-are-coming-for-you-22347343/
The MacBook supports 4k. At what refresh rate, we don't yet know.
See above. That's not how it works. USB is only using part of the pin set in those cables.
Correct, I wasn't clear. I thought he meant using the USB to transfer the video (we do have USB monitors) which won't be possible because USB itself isn't fast enough, that's why I quoted "data" as in the USB 3.0/3.1 specs.
DP1.3 will be fast enough and can be used in the USB Type C setup later in the future.
However, the Macbook will not support 5k monitor which is what we're talking about, the initial DP1.2a protocol in the USB Type C setup that Apple is using won't support it. Your own article said this as well.