{
  "$type": "site.standard.document",
  "canonicalUrl": "https://deterministic.space/pascal-vs-usb-c.html",
  "path": "/pascal-vs-usb-c.html",
  "publishedAt": "2016-12-18T00:00:00.000Z",
  "site": "at://did:plc:x67qh7v3fd7znbdhauc45ng3/site.standard.publication/3mjcd2t6afe25",
  "textContent": "Update: Got the laptop, and some adapters. Updated the post below with concrete tests and benchmarks where appropriate.\n\nI'm gonna buy a 15″ MacBook with 4 Thunderbolt 3 Ports because\n(a) I need new laptop,\n(b) I want to continue to use macOS (without hassle), and\n(c) I really like the premise of USB-C with alternate modes and Thunderbolt 3 with 40Gb/s.\nSadly, that means that I'll need adapters to connect all the hardware I currently own.\n\nHow hard can it be to find some adapter-y dock-y things[^adapters-n-docks] that I can actually afford? Let's find out!\n\n[^adapters-n-docks]: What is an adapter and what is dock? I'm using these terms pretty loosely. One way to differentiate might be to say an adapters is passive, while a dock has chips that actively transforms protocols for other physical ports. Or, a dock is large and expensive while you can buy a cheaper adapter that fits in your pocket. Or, a dock has more ports that are faster. For USB-C, these seem mostly equivalent, assuming that turning one USB-C connection with multiple alternate modes into a bunch of ports is not an \"active\" transformation as the host computer does all the hard work. Thus, a thing that has USB-C on one side, and HDMI or DisplayPort or the other, is an adapter. It gets fuzzy when an adapter has an ethernet port, as that most certainly means it has a dedicated chip for doing network stuff (that could also be USB 3.0 ethernet thing). Does this mean it becomes a dock? I'll say no. So, I'll settle on a simpler way to differentiate docks and adapters here: Docks are expensive. And good docks use Thunderbolt 3. That should make everything clear…\n\nWhat I want to connect\n\nHome office\n\nStatic setup, I put devices where I want them to be and they stay there.\n\n- Dell 4k display (3840×2160 @ 60 Hz) via HDMI 2.0, DisplayPort, or Mini DisplayPort\n- USB-A for display's USB 3 hub (mouse and keyboard as well as charging cables attached)\n- USB-A for external hard drives and such\n- Gigabit ethernet\n- Headphones via 3.5mm jack\n- USB-C charger\n\nActual office\n\nSemi-static setup. Will probably only need to move to another place when I least expect it (per Murphy's law).\n\n- Cinema Display or similar, 1920×1200 @ 60 Hz, HDMI or DVI connector\n- USB-A for mouse and keyboard (mouse actually plugged into Apple keyboard so one USB-A port should suffice)\n- Gigabit ethernet\n- Headphones via 3.5mm jack\n- USB-C charger\n\nOn the road\n\nIt's a laptop. I want to use it at random other places.\n\n- HDMI beamer\n- USB drives with USB-A\n- USB-C charger\n\nUnderstanding USB-C and its limitations\n\nCables\n\nThere are active and passive USB-C cables, as well as those that allow the full range of possible voltages and wattages of power delivery (5 V, 12 V, and 20 V for up to 100 W).\n\nA bunch of people seem to really enjoy testing USB-C cables. Good for them! Two rather famous gentlemen in this scene are [Nathan K.], and [Benson Leung]. Nathan has a nice [table comparing USB-C cables][usb-cables].\n\n[Nathan K.]: https://plus.google.com/102612254593917101378\n[Benson Leung]: https://plus.google.com/+BensonLeung\n[usb-cables]: https://docs.google.com/spreadsheets/d/1vnpEXfo2HCGADdd9G2x9dMDWqENiY2kgBJUu29f_TX8/pubhtml\n\nFor some reason there is no cable that does it all (Thunderbolt 3 with full 40Gb/s and 100 W power). Maybe I just missed some details there, though. 100 W power always come from 5 A at 20 V, but 60 W can come from either 12 V with 5 A, or 20 V with 3 A. Making long, 100 W USB-C cables capable of transferring 10Gb/s seems to be hard: Half of them are rated \"bad\", and they are a most 1 m. (The one from Apple is 2 m long but only supports USB 2.0 speed).\n\nDisplayPort\n\nAccording to [Wikipedia][usb-c-alternate-modes], USB-C supports DisplayPort up to protocol version 1.3 (handy [DisplayPort versions overview][dp-versions]). 1.2 and higher support 4k (3840 × 2160) with up to 75 Hz, so we don't need to worry about anything.\n\n[dp-versions]: https://en.wikipedia.org/w/index.php?title=DisplayPort&oldid=755497571#Resolution_and_refresh_frequency_support_for_DisplayPort\n\nIf I understand the Wikipedia page correctly, it also says that while using DisplayPort alternate mode, it is always possible to additionally use PowerDelivery and USB 2.0 over a USB-C cable. Spoiler alert: I'd really like to have this but there are currently no adapters that have USB Type C on one side and DisplayPort as well as another Type C port for Power Delivery on the other side. The closest I could find was the [Arc Hub][arc] (see table below for specs) but it ships early 2017 and there are no reviews available yet.\n\nFurthermore it allows an additional USB 3.1 connection if the DisplayPort mode only uses 2 lanes. I have no idea when that is the case, though. (4k @ 60 Hz over DP 1.2 uses up to 21.6Gb/s of bandwidth already!)\n\nDeep dive into HDMI alternate mode\n\nAccording to [Wikipedia][usb-c-alternate-modes], USB-C's HDMI Alternate Mode only supports HDMI 1.4b. Thus, passive docks/adapters that have HDMI ports will only support HDMI 1.4b. Which does not support 4k @ 60 Hz ([HDMI version comparison]). That's bad.\n\n[usb-c-alternate-modes]: https://en.wikipedia.org/w/index.php?title=USB_Type-C&oldid=754888380#Alternate_Mode\n[HDMI version comparison]: https://en.wikipedia.org/w/index.php?title=HDMI&oldid=755507256#Version_comparison\n\nHDMI 1.4b does support some cool stuff like Consumer Electronic Control (CEC; remotes work across devices), 3D video, Dolby TrueHD, and an Ethernet channel. I'm not sure how much of that will actually work through adapters, though. According to reviews, some adapters don't even support 4k with 30 Hz.\n\nWikipedia [mentions][hdmi-alternate-mode] some other quite interesting details:\n\n[hdmi-alternate-mode]: https://en.wikipedia.org/w/index.php?title=HDMI&oldid=755507256#HDMI_Alternate_Mode_for_USB_Type-C\n\n> From a HDMI video source, 3 TMDS channels and TMDS clock signal are carried over the USB Type-C super-speed data pins. The DDC clock, DDC data, CEC signals are carried over 1 configuration pin. The HEC/ARC, HPD signals are carried over 2 side-band pins on the USB Type-C connector.\n\nIf you know the USB-C layout, this sounds like it pretty much uses the whole thing. And, Wikipedia goes on:\n\n> Hence HDMI alternate mode provides a simultaneous video out and USB 2.0 data transfer facility. The USB 3.1 data transfer modes will be only available when video out is not in use, as they need the super-speed pins for these modes.\n\nDamn, that sounds… bad. But let's backtrack a bit. What are these abbreviations we just read?\n\nTMDS\n:  Transition Minimized Differential Signaling\n:  \"interleaves video, audio and auxiliary data\"\n\nDDC\n:  Display Data Channel\n\nCEC\n:  Consumer Electronic Control\n\nHEC\n:  HDMI Ethernet Channel\n\nARC\n:  Audio Return Channel\n\nOkay, of those we can probably get rid of HEC and ARC, as we want to do Ethernet over RJ-45 (i.e., another port on the adapter), and while an audio return channel (i.e. audio input over HDMI) is nice, I'd be surprised if the MacBook knows how to handle it. Sadly, the same is probably true for CEC -- which I'd like to have! Adjusting my AV receiver's volume without using the remote would be amazing.\n\nWhat does that leave us with? The hope to at least have HDMI, ethernet, and maybe even USB 3.0 (5Gb/s)!\n\nIt's a conspiracy!\n\nWhat's crazy is this: There are adapters that have all these ports. HDMI, ethernet, multiple USB 3.0 (USB-A) ports, even SD card slots, and \\gasp\\ VGA[^hdmi-vga]. How does that work? Has anyone tested this and measured what throughput they get over the USB-A ports?\n\n[^hdmi-vga]: Like Dell's \"470-ABRY DA200\" adapter. Even Dell itself [mentions][dell470] that you can only use one of HDMI and VGA at the same time, though.\n\nOr, and here's a crazy idea: These are actually active adapters using _DisplayPort_ alternate mode and convert to HDMI! You want proof? Here the product description of i-Tec's \"USB C Travel Docking Station\" (from [their website][itec]):\n\n> Hardware requirements: notebook, tablet, PC or smartphone with OS Windows, Mac or Google with a free USB-C port with \"DisplayPort Alternate Mode\" and \"Power Delivery\" support or Thunderbolt 3 port\n\nNo HDMI alternate mode mentioned anywhere. I'm fairly certain this description is plain wrong, though. A bit earlier it says this is \"1x HDMI, max. resolution 1920x1080 / 60Hz\" and \"it allows to transfer video and stereo audio\". Surely, they did not build a converter from DisplayPort to HDMI, _and_ added an external sound card, _and_ convert all that to an HDMI compatible TMDS stream, when they could just use HDMI alternate mode. They wouldn't, would they?\n\nUpdate with benchmarks\n\nUsing the i-tech dock (see below), I can connect my TV (1920×1080 @ 60 Hz) over HDMI, and still use Ethernet as well as two USB 3 ports without any problems (one just connects to the USB 3 hub in my main display, with mouse and keyboard connected). Benchmarking two external USB 3 drives (one 2.5″ 2TB HDD from Segate, and one Sandisk SSD with a separate SATA 3 to USB 3 adapter), I can't find any difference between connected the drives using an Apple USB-C-to-A adapter and connecting them to the dock (with HDMI and Ethernet also connected). Both drives are not _that_ fast, though: The SSD's top speed was 235 MB/s which is still well below the theoretical top speed of 5 GB/s (625 MB/s) of USB 3. Oh, and did I mention my 4k display also works with this dock (@ 30 Hz, of course)?\n\nMHL\n\nOh, you thought I was done talking about displays? Sorry!\n\nThere is also an MHL alternate mode over USB-C which seems to support everything you can possible want from a display connector (up to 8k @ 60 Hz with power delivery and USB 3.1 Gen 2 data). The [official \"USB Type C\" page][usbc-mhl] has a FAQ with these claims, but their product page does not currently list any Apple devices.\n\n[usbc-mhl]: http://www.mhltech.org/usbtype-c.aspx\n\nDVI\n\nA lot of the displays I use are older Cinema Displays that have DVI-D cables. But that's okay, single-link",
  "title": "Pascal vs. USB-C",
  "updatedAt": "2016-12-18T00:00:00.000Z"
}