One-Cable Docks: What the Bandwidth Actually Buys
A dock promises a desk that connects with one cable. We loaded five of them with everything at once and measured what gave way first.
Tech Daily Review Desk
What actually changed
USB4 and Thunderbolt 5 pushed the headline bandwidth figures up again, and one-cable docks are sold almost entirely on those numbers. What none of the boxes explain is that the bandwidth is shared, and that the display takes its share before anything else gets a look in.
Everything on the dock shares one link back to the laptop. A 4K display at 60 Hz is a large, constant reservation from that link; a second one is another. What is left over is what your drives, your webcam and your network adapter divide between them. Some docks work around this by compressing the video stream or by driving the second display through a software adapter, and both of those workarounds have costs that show up somewhere else.
Why this is worth your attention
Because the failure is not a message saying you have run out of bandwidth. It is a second monitor that will not go above 30 Hz, a webcam that stutters during a call, or a backup that takes all afternoon — and none of those symptoms point at the dock.
How the testing worked
Five docks on the same laptop, each loaded with the full set at once: two 4K displays, a sequential read from an external SSD, a 1080p webcam in a live call, wired networking and a keyboard and mouse. We measured achieved drive throughput, dropped webcam frames over ten minutes, the refresh rate each display actually negotiated, and the power the dock delivered back to the laptop while all of that was running.
What we recorded
| Dock | Displays achieved | Drive read | Webcam drops | Charge delivered |
|---|---|---|---|---|
| Thunderbolt 5, 140 W | 2 × 4K 60 Hz | 2,810 MB/s | 0.1% | 94 W |
| Thunderbolt 4, 90 W | 2 × 4K 60 Hz | 1,190 MB/s | 0.3% | 86 W |
| USB4, 100 W | 2 × 4K 60 Hz | 720 MB/s | 2.1% | 71 W |
| USB-C 3.2, 65 W | 4K 60 Hz + 4K 30 Hz | 410 MB/s | 6.8% | 48 W |
| USB-C with software adapter | 2 × 4K 60 Hz | 380 MB/s | 11.4% | 45 W |
What the figures say
Every dock drove two displays on paper; two of them did it by dropping a panel to 30 Hz or by compressing in software, and both were obvious to look at.
Drive throughput is where the shortage shows up first and most dramatically — a factor of seven between the best and worst dock on identical hardware.
The software-adapter dock cost the most in webcam frames because it is spending processor time on video, which is the resource a video call also wants.
Charge delivered was consistently 20-30% below the number on the box once everything else was running, and on the 65 W dock the laptop slowly discharged under load.
Caveats
Three things worth holding on to when you meet these figures somewhere else:
- A dock rated for "dual 4K" may mean 30 Hz on the second panel, which is unpleasant to use and is never said out loud
- The wattage on a dock is what it can supply in total, not what reaches your laptop with six things plugged in
- The cable counts — two of our docks lost half their throughput on a passive cable that physically fit perfectly well
What we would buy
Work out your display requirement first and buy for that, because it is the load with no flexibility in it. If you want two 4K panels at 60 Hz with anything else happening at the same time, that is a Thunderbolt 4 dock as a floor. One display leaves plenty of room and a much cheaper dock will do the whole job properly.
Avoid docks that drive displays through a software adapter unless you have no alternative. They are cheaper and they work, but the cost lands on the processor, which means it lands on your video calls and your battery — the two things a docked laptop is most often doing. Check the cable too: ours cost half the throughput of the entire dock.
Where we land
The bandwidth is shared and the displays take it first. Thunderbolt 4 is the practical floor for two 4K panels plus real work; below that something quietly gives way, and it is usually the drive.
Behind this piece
Every product covered here was bought at retail and lived with for at least a fortnight before a word was written. Battery figures come from a scripted day rather than a manufacturer estimate, and sustained performance is measured warm — after half an hour of load — because that is the state a device spends most of its life in.
Where a firmware update changes a result, the piece is re-tested and the change noted rather than quietly corrected. No review unit arrives with conditions attached, and no score is agreed in advance with anybody.
Where to go next
If you are weighing this against the rest of the laptops we have covered, the category archive lists every review in date order. The closest comparisons we have published are Razer Blade 16 Review: Competent but Outclassed and Razer Blade 16 Review: Power at a Cost.
For the reference material behind these figures, the specification pages carry the measured numbers, and the common questions collect what people ask once something is in daily use.
