Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I bought a flash recently, In the warranty card there was a caution saying "Always use USB ports on the back of the case" . Is there any difference between front and back ports? They are all connected to the MoBo the same way providing the same voltage, functionality etc?

share|improve this question
+1. I'd like to know as well! – AbhishekGirish Dec 27 '12 at 18:06
a simple google search gave me this info - yes there is a difference! Mainly to to do with power. Hence it affects performance. The back ports have more power capability – AbhishekGirish Dec 27 '12 at 18:10
and you are less likely to bump the computer and disconnect the plug when its on the back. for stuff like flashing a phone's rom over usb, it is always recommended you use back ports, both for power and stability. – Frank Thomas Dec 2 '13 at 13:01
up vote 13 down vote accepted

I have had motherboards in the past that provided usb 1 on the headers (which connected to the front of the case), and provided usb 2 to the ones mounted/attached to the back of the board itself (aka the back ports).

This is purely a design choice made by the board designer(s).

With respect to your flash-memory stick, the manufacturer of that device is gambling on the idea that the ports on the back are going to be the highest supported standard at the time of the board's manufacture. Since they did not design your motherboard, they have no way of knowing for sure.

They need to make a statement for the people most likely to need the statement made. More technically minded individuals will probably know that the generalization made int he manual is too narrow. For the less technical, if they follow what is written, they are more likely to not have problems with the device.

Oversimplification is a common teaching tool, and one of the reasons that technical fields must re-teach certain subject at the college level to correct these errors or over-specifications in high school level classes.

share|improve this answer
"With respect to your flash-memory stick", I liked that ! So, You believe it's an "Oversimplification" & presumption ? – Sam Dec 27 '12 at 18:23
Similar -…. I came to the same conclusion, that it's up to to how the motherboard maker wants it to be. Only other possiblity I can think of is that the rear are built on the board, but the front require a cable, which could possibly get connected wrong and either not work right or cause damage. – Bratch Dec 27 '12 at 18:25
@sam: yes, I think so. – horatio Dec 27 '12 at 18:28
The front ports could damage the card if the the +5V and -5V wires are inverted. – Fábio Dec 27 '12 at 19:11

There is a difference in power level only, as some device needs high power (500 mA instead of 100) to charge or function. Where the port is located does not matter. Not sure what it means really in your warranty card. You might ask the manufacturer. Many of my devices such as netbooks and laptops have ports on the sides, neither back nor front, actually.

share|improve this answer
Which ports provide 500mA & which ports 100 mA? And why is that? isn't the way they connect to MoBo the same? – Sam Dec 27 '12 at 18:18
you should check your computer manual or your OS facilities such as control panel/device manager or something similar on your OS. For instance, my windows 7 pc device manager tells me that my usb root hub is 500 mA. My old laptop however only has 100mA usb ports. – johnshen64 Dec 27 '12 at 18:29

It depends entirely on the motherboard. With my motherboard (Sabertooth X58) there are two rear USB 3.0 ports and that's it. The rest of the rear USB and the front USB are 2.0. Older boards had a similar dichotomy regarding 2.0/1.0. Some modern boards have less 3.0 ports to reduce costs (but usually use 3.0 up front). However, there is no reason I am aware of for front USB to be "dangerous" to a device, just sub-optimal for those boards with no front 3.0.

share|improve this answer

well there are no performance issues. the front ports are part of the cabinet and the back ports are part of motherboard.(but the front ports are also attached to the motherboard using wires.) Back ports are used to provide more sockets for connecting peripherals on back. and the front one are for easily and quickly removable peripherals.As the back ports are soldered to MB it is better to use them less frequently. but its up to user.

share|improve this answer

Actually by "Always use USB ports on the back of the case" they probably mean: don't use extension cables or hubs but use a "real" usb port.

share|improve this answer

Yes, there are differences between them. The back USB ports are controlled by GMCH (graphics memory controller hub), which is directly operated by rich (south bridge) whereas the front ports are controlled by I/O controller. GMCH controlled back USB ports give more power and directly connect the device to the motherboard unlike the front, which work on system IRQ.

share|improve this answer
This would be the design choice for some but not all computers from a decade ago. South bridges went out of fashion quite a while ago. – MSalters Jul 29 '14 at 14:44

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.