Questions about USB 2.0 vs 3.0

[Mike Buckley]

I realize that USB 3.0 is faster than USB 2.0 when transferring data. Is that also true when recharging a battery?

Why do so many computers have, as an example, just one USB 3.0 port and one or two other USB 2.0 ports? Why would not all of the ports on a computer be USB 3.0?

[DanK]

I can only guess. I am guessing that the answer to the first is 'no,' since charging will depend on voltage, not the speed of signal transmission. My guess with respect to the latter is cost. My Dell desktop, which is now a few years old, has a handful of USB 3.0 ports and considerably more USB 2.0. Oddly, only one of the USB 3.0 ports is on the front of the case, where they are most useful.

[PhotomanJohn]

It is true that later version USB ports (depending on the manufacturer) can provide more current on their 5V output for powering devices with larger power requirements and charging batteries faster. The USB ports on this MacBook Pro can deliver above 2A for battery charging.

The amount of current drawn for battery charging is often controlled by the charging circuit in the device being charged so it may not charge faster on a USB port that is capable of higher current. This is true with iPhones where the older ones will only draw 1A no matter what and the new ones will draw 2A for battery charging if available.

[Mike Buckley]

When they [Apple] went to USB 3, all ports became USB 2 & 3 compatible.

Any USB port will be forward- and backward-compatible but only to the extent that the limitations of the older version will be in effect.

[Manfred M]

I suspect that the reason that there manufacturers have not gone with 100% USB 3 ports is cost. Saving a few pennies per machine over the millions that are built adds up to a fair bit of money.

[Geoff F]

I have 6 USB ports on my computer and when I connect my camera, or other equipment, I get a notice telling me that using a USB3 port would be faster. I have tried all 6 ports and get the same response from all of them.

[DickyOZ]

I have 6 USB ports on my computer and when I connect my camera, or other equipment, I get a notice telling me that using a USB3 port would be faster. I have tried all 6 ports and get the same response from all of them.

Are you sure your USB ports are actually USB 3 ports? If they are only USB 2 and you plug a USB 3 device into them you will get that message. If they are USB 3 ports you almost certainly have a Windows driver problem; I had all sorts of problems getting Windows 7 to recognise the USB 3 ports as USB 3 on my motherboard.

[george013]

Are you sure your USB ports are actually USB 3 ports? If they are only USB 2 and you plug a USB 3 device into them you will get that message. If they are USB 3 ports you almost certainly have a Windows driver problem; I had all sorts of problems getting Windows 7 to recognise the USB 3 ports as USB 3 on my motherboard.

Is that possible? The USB3 plug is bigger as the USB2 plug. Unless you use the wrong cable, a USB2 cable for a USB3 device.

Last year I bought a Medion PC with USB3, all kind of problems with USB3. I just builded a new PC myself, I didn't test the USB3 ports yet. I must have also a special USB port that allows me to charge a device faster.

George

[Mike Buckley]

The USB3 plug is bigger as the USB2 plug.

The ports are the same size on all three of my computers. My understanding is that the plugs are also the same whether using USB 1.0, 2.0 or 3.0.

The size of the ports and thus the plugs varies on my cameras but I don't know if that's related to the USB version. I don't even know the version of the USB on my cameras.

[Dave Humphries]

Chapter and Verse on USB at Wikipedia

No, I haven't read it all, but skimming through answers all questions above
(much of which I didn't know)

I have put links to specific parts of the (very long) page to help you zero in on what interests you.

Transmission rates

Connector types/pin-outs.

Seems the colour of the plastic insert denotes the port version;
Black or White = USB 1 or 2
Blue = USB3
Teal Blue = USB3.1
Other colours (Red, Orange, Yellow) for 'sleep and charge' functionality

Power delivery (over-simplified):
USB2 = 500mA
USB3 = 900mA
at 5v +0.25v

Cheers, Dave

[pnodrog]

USB is a very useful interface but a bit of a can of worms regarding exact configuration/cable/connector/current rating etc. Reasonably backward compatible.

For more info https://en.wikipedia.org/wiki/USB#Charging_ports

I see Dave beat me to it.. As a good moderator should.

[Mike Buckley]

Power delivery (over-simplified):
USB2 = 500mA
USB3 = 900mA
at 5v +0.25v

Over-simplified? You over estimate my capabilities, Dave. Larger numbers generally means better except for the size of waist lines, so should I assume that 900mA charges a battery faster than 500mA?

Seems the colour of the plastic insert denotes the port version;
Black or White = USB 1 or 2
Blue = USB3

What is the result of placing a plug that has a blue insert into a port that has a black or white insert and vice versa?


Now you understand why I didn't even bother looking at Wikipedia.

[Dave Humphries]

~ so should I assume that 900mA charges a battery faster than 500mA?

Probably - as long as the charger is rated for it.

It is over simplified because there are special ports with much higher current ratings for special cases - typically found on older laptops, these were to power the early USB-powered external HDD (rather than 'wall-wart' powered HDD). Alternatively, those drives might have had a Y cord to connect to computer so as to draw power from two ports to avoid frying the tracks on the laptop's circuit board if they succeeded in getting enough out of one.

[Dave Humphries]

What is the result of placing a plug that has a blue insert into a port that has a black or white insert and vice versa?

Most likely what you'd expect

e.g. Probably not a lot of difference.

I doubt the conductors would melt in an older, USB 1 or 2 cable (which might be coloured black/white) if plugged in to a (blue) USB3 port and used to charge at 900mA.

The other way round won't be an issue because the limiting factor is the port supplying the power. So if you had a blue insert cable (which might have thicker conductors) and put it in to an older, USB 1 or 2 port, which could supply just 500mA, it won't matter.

I can only apologise for the excessive use of; 'might', 'probably' and 'doubt'

[Mike Buckley]

Most likely what you'd expect

I doubt the conductors would melt in an older, USB 1 or 2 cable (which might be coloured black/white) if plugged in to a (blue) USB3 port...

I sure wouldn't expect any chance of anything melting! Yikes!

For the record, I inserted a black plug into a 3.0 port today for a couple of hours while the battery was charging and nothing melted. At least nothing on the outside melted. Whew!

[lunaticitizen]

I realize that USB 3.0 is faster than USB 2.0 when transferring data. Is that also true when recharging a battery?

Why do so many computers have, as an example, just one USB 3.0 port and one or two other USB 2.0 ports? Why would not all of the ports on a computer be USB 3.0?

The answer for the second question:

It's the design of the chipset's manufacturers (i.e. Intel, AMD, etc). For example, Intel B85 chipset that can be found in many inexpensive motherboards, specifies 4 ports of USB 3.0 and 8 ports of USB 2.0.

Why did they design it like that? Well, the USB part of the chipset is limited in bandwidth. For example, if the chipset has 25 Gbps of bandwidth and it has to divide them between USB 3.0 (5 Gbps) ports and USB 2.0 (0.5 Gbps) ports, then you have several design options.

• 5 USB 3.0 ports (5 x 5 = 25 Gbps) and no USB 2.0 ports
• 4 USB 3.0 ports (4 x 5 = 20 Gbps) and 10 USB 2.0 ports (10 x 0.5 = 5 Gbps)

Which one would you choose? Personally I'd choose the design that has USB 2.0 ports too. My wireless mouse and wireless gamepads don't need the speed of USB 3.0, so I can just plug them to the USB 2.0 ports. For anything else I'd use the USB 3.0 ports.

[Mike Buckley]

That makes sense, Leo. Thanks for the explanation!

[Simon Garrett]

The answer for the second question:

It's the design of the chipset's manufacturers (i.e. Intel, AMD, etc). For example, Intel B85 chipset that can be found in many inexpensive motherboards, specifies 4 ports of USB 3.0 and 8 ports of USB 2.0.

Agreed. Later chipsets support more USB3 ports. E.g. the Z97 used with Haswell and Broadwell processors support 14 USB ports, of which 6 can be USB3. With the Z170 chipset used with latest Skylake processors it's 14 USB, of which 10 can be USB3. Most motherboards won't support that many in practice.

[pnodrog]

Leo's explanation of the relationship between band width and USB3/USB2 port allocation clears it up nicely.

However with regard to the speed of recharging batteries other factors such as power supply, cable/connector used and most significantly the batteries charging control electronics and the batteries characteristics. Simply increasing the current available may allow more batteries to be charged at once or higher capacity batteries to be charged but not necessarily much faster.

Giving a pedestrian a wider better footpath may result in him being able to stroll along with more mates but he may not walk much faster....