MacBook, Dongle-dom & "Single port life"

jingo_man

macrumors newbie
Original poster
Nov 11, 2018
17
6
  1. How is life with only 1 port?
  2. What are the restrictions with non-Thunderbolt 3 compatibility? I am presuming today there aren't many devices though this may change. Is the 5Gbps upper limit an issue, or is this just for "pro" use, i.e. multi-5k screens, plus TB3-native SSDs or eGPUs?
  3. Is there any system performance overhead when devices are attached? i.e. will I lose base CPU cycles as a result?
The Air has the distinct advantage here, but if life is bearable with the example use cases below, it becomes another acceptable compromise for the form factor.

I foresee 2 main scenarios where I will need or like to use peripherals:
  • Remote & presenting - laptop on the road, doing customer sessions or presentations. I need power + HDMI connectivity
  • Office dock - power + external monitor (HDMI) + external hard drive
The HDD may store something like a VM image, though I have previously used USB3 speeds with this type of setup, for my needs.

Monitors sound a little more complex, whether it is 1080p, 4k or 5k. Is there a simple explanation? Today, i have 1x 1080p monitor, but I have been looking at the Ultra Wide screens from LG (4k?). Can the TV provide the power to itself and the MacBook? Is it connected via a HDMI port or a USB-C port?

Ideally I would be looking for a USB-C hub with:
  • passthrough power
  • HDMI
  • up to 3x USB-C ports
  • up to 2x USB-A ports
  • ethernet(?) - more optional and nice to have (in 2018 with WiFi, etc)
Are there recommendations for this type of configuration? Preferred vendors?
 

EugW

macrumors 604
Jun 18, 2017
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4,685
98% of the time I don’t carry a big hub but I have a USB-A to USB-C adapter on my keychain with me at all times. That’s really all that I need except for video dongles if I’m giving a presentation.

Nonetheless I have purchased a multifunction hub to use when necessary, such as on business trips.

The lack of higher bandwidth or Thunderbolt means that the all-in-one dongles are problematic in some situations. Specifically, one cannot get 4K 60 Hz video support and USB 3 at the same time. It’s either 4K 60 Hz plus USB 2 or else 4K 30 Hz plus USB 3.

So, in addition to my all-in-one hub (with SD, USB 3, Gigabit Ethernet, 4K 30 Hz HDMI), I also bought a dedicated 4K 60 Hz HDMI dongle.

Ideally you should get dongles with power passthrough when you plan on using them for extended periods, as you suggested. My keychain USB-C adapter is fine without power passthrough since I just use it for a few minutes at a time for say transferring files from a USB stick. However, for the big hub and the 4K 60 Hz HDMI adapter I got ones with power passthrough. I also have a VGA adapter with no power passthrough.

If you really are considering using your laptop a lot with an external 4K screen and hard drive simultaneously though then you really want a Mac with at least 2 USB ports. In my case the laptop is usually not used this way, since my main machine is a 5K iMac which also has an attached 2.5K iMac as a second monitor. I have no need to make the laptop into a desktop replacement. So, having just the one port on the MacBook hasn’t been a significant problem for me in real world usage.

BTW, the other issue I noticed with my Anble multifunction hub is that if I have multiple devices connected, if I unplug one, it can sometimes disconnect all of them. This is true even on passthrough power. Not sure if it’s just my specific hub though.
 
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jingo_man

macrumors newbie
Original poster
Nov 11, 2018
17
6
Thanks @EugW

The USB-C world just seems so confusing! So I can drive the monitor using HDMI, Display Port or USB-C, which have varying throughputs? Great.

Does connecting monitors affect the CPU performance, to drive it? Or is if H/W offloaded again?

Are there dongles that have more than 1 USB-C inputs? So in addition to a passthrough power, I also get a 2nd or 3rd USB-C port? Would the throughput of either or both be constricted in this setup?

Most likely, I would replicate your setup and expect to have a travelling arrangement of dongles, plus a beefier hub. A-to-C on the keychain is a good idea though.

In all scenarios though, I need to consider that this device should be my main device. My "standard" setup at home has power & 1080p monitor (today) plugged in at my desk. Most others are wireless connections, or short connections that I could replace the power. Can the MacBook support 2x 1080p monitors, plus power?

Stumbled upon this thread, that shows a monitor with built in USB-C PD (hub) inside the monitor. This may actually be the perfect setup, as the title suggests!
 

theluggage

macrumors 601
Jul 29, 2011
4,033
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The USB-C world just seems so confusing! So I can drive the monitor using HDMI, Display Port or USB-C, which have varying throughputs? Great.
Actually, a display connected via USB-C* is always DisplayPort as far as the computer is concerned. 'USB-C displays' are effectively DisplayPort, (current) USB-C to HDMI cables incorporate a DisplayPort-to-HDMI converter.

Lets try and simplify the essentials:
  • A USB-C cable has 4 pairs of wires to carry high-speed data, each of which can carry either USB 3 or DisplayPort - but not both. The cable also has a dedicated set of wires for old-school USB 2 as a fall-back.
  • Current USB-C ports can only use 2 of those at a time for USB (one for out, one for back) - you'll only get 1 USB 3 port "worth" of USB bandwidth out of a USB-C port. The MacBook doesn't support the faster, 10Gbps USB 3.1 speed, either.
  • A regular DisplayPort cable has 4 pairs, but doesn't always use all of them.
  • An old-school 1080p display only needs 1-2 pairs, but a 4k display at 60Hz needs all four. Connect a 4k@60Hz display and the only capacity left for USB is the "fallback" USB2 facility.
So, on a USB-C hub/dock/multiport adapter:
  • Any USB, Ethernet, SD card slots are sharing a single USB-3 port's worth of bandwidth
  • They can do that alongside a 1080p or 1440p display - but connect a 4k@60Hz display and the other ports have to share one USB 2 connection...
A USB-C display with an integrated hub won't do 4k@60Hz and be a USB 3 hub, either (the Apple/LG Ultrafine 4k display specifically says that the USB ports are 2.0 only - the 5k version is a thunderbolt display so different rules apply and it won't work with the MB).

NB: Yes, you can run 4k at 30Hz and halve the bandwidth - which might be fine for presentations or playing video (its not as if 30Hz LCD displays actually flicker at 30Hz) - but you wouldn't want that as a long-term solution for an interactive desktop: windows will jerk/tear as you drag them, the mouse pointer will disappear/flicker if you move it too fast...

My "standard" setup at home has power & 1080p monitor (today) plugged in at my desk.
Well, that should be OK - with a multiport adapter, the MacBook should manage a USB 3 drive and a 1080p display. Not that the Macbook is ever going to give you the smoothest, slickest experience you could ask for.

However, if you want to upgrade to 4k and/or multiple displays, or connect multiple external drives (and care about their performance) then, basically, the MacBook is not meant for you. Even disregarding the connectivity, you want something with a better GPU to drive multiple and/or 4k displays smoothly.

The MacBook - and the new Air - are designed for maximum portability, and its great that they can be hooked up to a 4k display is great, but if that's your primary purpose then you should be looking at the MacBook Pro.

* There are lots of ifs/buts/unlesses/ors/coming soons in the wider world of USB-C, of course, but I'm specifically talking about the non-Thunderbolt USB-C port in a MacBook here.
 

EugW

macrumors 604
Jun 18, 2017
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theluggage said:
However, if you want to upgrade to 4k and/or multiple displays, or connect multiple external drives (and care about their performance) then, basically, the MacBook is not meant for you. Even disregarding the connectivity, you want something with a better GPU to drive multiple and/or 4k displays smoothly.
Are you suggesting a single 4K 60 Hz display would be a problem for the GPU too?

I tried 4K 60 Hz briefly over 4:4:4 HDMI and it seemed fine for performance. (I didn’t test longer though because I already have a 5K iMac.)

Of course, it would be limited to USB 2 though, although in my case it’s moot since my 4K 60 Hz dongle has no USB at all.
 

jingo_man

macrumors newbie
Original poster
Nov 11, 2018
17
6
* There are lots of ifs/buts/unlesses/ors/coming soons in the wider world of USB-C, of course, but I'm specifically talking about the non-Thunderbolt USB-C port in a MacBook here.
Can I briefly ask how different the world is for the Air 2018, with its 2x TB3? Purely having 2 ports will allow me to have USB-C PD + 4K@60Hz.

It doesn't have a significantly more powerful CPU, not sure about GPU, but how much more capable is it?
 

EugW

macrumors 604
Jun 18, 2017
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If you need it, TB3 x 2 is much, much more capable than USB-C x 1.

In my case though I don’t really need it, since I have a separate desktop. It would still be nice to have though.
 

theluggage

macrumors 601
Jul 29, 2011
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Are you suggesting a single 4K 60 Hz display would be a problem for the GPU too?
I'm just suggesting that a 4k display means moving 4x as many pixels as a standard-def display and the MacBook has the absolute bare minimum of integrated GPU designed at running the internal display plus, maybe a TV or projector. Also, unlike Windows, MacOS only lets you set the system text/icon size on a 4k display by using GPU-intensive fractional "scaled modes". There's been some reports in another thread about the new Mini (which has a better GPU) getting sluggish with Photoshop (basic panning and zooming a photo, not some power-guzzling multilayer compositing) in "looks like 1440p" scaled mode - and remember the MacBook will always be driving two displays.

If it works for you, great - and its in the specs so it should work. I'm just saying that if one of my primary purposes was driving a 4k display, I'd go for something with a bit of "headroom" on the GPU front, and Thunderbolt over USB-only - and its not as if the MB is drastically cheaper than the non-TB MacBook Pro (although I'd wait for that to get the 3rd-gen keyboard - sigh).

Purely having 2 ports will allow me to have USB-C PD + 4K@60Hz.
You can have 4k + USB-C PD (Power Delivery) on the MacBook with a suitable multiport adapter or a USB-C display - but not run a USB device at USB 3 speeds at the same time.

The two ports on the Air mean you could have a 4k display in one, a USB 3 device in the other and either one could be via a hub/adapter that also gave you power.

Also, the Air's ports support Thunderbolt which gives you other (if more expensive) options - a Thunderbolt 3 dock will run a 4k (or 5k) display, several full-speed USB 3 ports and power/charge the computer all from a single port on the computer. The dock will be 2-3+ times the price of a USB-C hub, though...

As I said, though, if running 4k display(s) is a big deal, though, I'd go for a MacBook Pro with a bit more graphics clout.