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I heard that one of the two USB ports provides more power, decreasing the charging time.

Still, I forgot which one is the powerful one. I would be nice to give a hint that's easy to rememeber ;)

It is does matter, this is a MBP from Early 2011, not one of the new 2012 series which has a very powerful charging port.

Update! I checked using System Report (you need to restart it after you plug/unplug iPad as it does not refresh itself).

So far there is no difference on my MBP, it it provides is 500 mA which is quite low.

Current Available (mA): 500
Current Required (mA):  500
Extra Operating Current (mA):   1600

This is a very interesting question. Apple has a support article about powering peripherals through USB. Apple states that each USB port is supplied with up to 900mA at 5V. There have been a few discussions brought up on various forums about port inequality that I have seen, but I don't think Apple has ever addressed any of the claims.

The users who suggested the inequality took it into their own hands to do a bit of testing; I found this very nicely written breakdown.

Sparing the technical details, they ran tests with the front & back USB ports and noticed very small differences. It also suggests that the keyboard/trackpad, memory card reader, and Bluetooth are all connected to the 'front port', and that iSight and IR reciever are connected to the 'back port'. Based on what is connected where and on the numbers from their tests, it appears as though the back port has slightly better performance.

This all said, the difference is so small you'd never notice it charging a device (especially from Apple). Using your iPad with either port is fine. There won't be a noticeable difference.

As suggested, you'll likely get better charging performance by using the wall cube, rather than charging via USB.

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You can use either port, the limitation is that only one USB port can provide this higher power level. If you try and charge two iPads at the same time, only one will get provided with the higher power level, and the decision as to which is made on a first-come-first-served basis.

Edit to Add: I forgot to mention that the article says Macs with more than two USB ports may be capable of powering multiple ports (but not necessarily all) at this higher power level. Unfortunately they don't give any further details.

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