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I searched for these questions but mostly I only find long articles about USB 3.1 and USB Type-C. After spending long time reading them, I remain with my questions unanswered. There’s no direct answer to them.

  1. I read that a USB Type-C port in a laptop can output 100W of power. Does a USB 3.1 Type-A port also output 100W or is it only the USB Type-C port?

  2. One of those 100W power ports should be able to power a 3.5" hard disk drive alone without additional power other than this single cable, right? Has anyone actually tested this?

  3. I have a hard disk drive with a few years already. I was thinking of upgrading it to USB 3.1 Type-A to make use of its better speeds. I read that all there is needed to do is get a new USB 3.1 Type-A external enclosure and move the hard disk drive from the old enclosure to the new one. However, I also read a couple comments saying that the speed will always depend on the actual hard disk drive. Does that mean it will have same speed on USB 2.0 as in USB 3.1? Or it will always be faster on USB 3.1, only not reaching the max speed?

  4. Assuming it will have same speed on both USB versions, what does make use of the max speed USB 3.1 says to support then? Is it the newest SSD’s?

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    I'm not entirely sure, but I think for a USB Type-A port, you need a charger port (can be recognized by their yellow ribbon instead of the blue one. Not sure if there's a 3.1 USB port that does both that is type-a though. – LPChip Dec 30 '17 at 16:31
  • “Assuming it will have same speed on both USB versions, what does make use of the max speed USB 3.1 says to support then? Is it the newest SSD’s?” USB 3.0 can support fast hard disk drive and SSD speeds. The speed of the USB 3.x pipeline is not for any specific usage; it simply is a speed that exists because the protocol is capable of that speed. – JakeGould Dec 31 '17 at 1:36
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  1. USB 3 implementations are limited to 9 W (1.8 A) for charging only, and considerably less when used for data transfer. USB-C ports are limited to 15 W (3 A), though USB-C cables may theoretically be able to handle 100 W.

  2. There are many external HDD drives available that can be powered by USB 3 or even USB 2 ports, e.g. this Seagate product. That said, it depends on the HDD and the power available... PC, other devices using power etc.

  3. It depends... whichever is slower sets the limit: HDD speed, enclosure speed, USB speed.

  4. Mileage may vary... it depends on the specifics.

  • Regarding number two the question is about “3.5" HDD” not 2.5" HDDs that are typically found in self-powered enclosures. – JakeGould Dec 31 '17 at 1:27
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As a general note, having separate questions would fit the site better.

Does a USB 3.1 Type-A port also output 100W or is it only the USB Type-C port?

You need the CC signal, the CC1 and CC2 pins in the USB C connector to negotiate Power Delivery.

One of those 100W power ports should be able to power a 3.5" hard disk drive alone without additional power other than this single cable, right? Has anyone actually tested this?

When Seagate announced the Innov8 in 2016 January they claimed it was the first USB powered desktop external hard drive. I am not sure whether there are any bare enclosures offering this.

Assuming it will have same speed on both USB versions, what does make use of the max speed USB 3.1 says to support then? Is it the newest SSD’s?

USB 3.1 Gen 1 is just USB 3.0 renamed, it's still five gigabit per second. Gen 2 is ten gigabits per second. According to Akitio , Gen 1 bottlenecks at 300-400 MB/s which is slightly below the actual speed of SATA 3 so most SSDs will get gimped. No HDD can achieve such speeds as of 2018.

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