How does the iPad charge in a Macbook Pro from 2007?

[Shorties]

I needed to sync my iPad overnight so I left it plugged into my Macbook Pro (Santa Rosa Chipset from 2007) in which it typically says "Not Charging". When I woke up the iPad was synced as expected, but it also was fully charged. (When I went to bed it was around 70%). I was just wondering at what point, and what are the conditions, for it to charge connected to my computer?

 

[Kupp]

I think it can charge on older systems, just very slowly and only so long as the ipad screen is off. I think that is what I have read, but I haven't tested that.

 

[c14nhl]

I've actually noticed that mines has displayed the fact it isn't charging. Only tried the one USB port, but I'd imagine it would be the same for them all.

 

[Stetrain]

Basically it should charge slowly when the screen is off. It can't both run the screen and charge the battery off of a low powered port.