Overloading your USB

Huntn

macrumors demi-god
Original poster
May 5, 2008
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The Misty Mountains
I just had an experience where I was running an external hard drive on one of my two USB ports on my MBP. On the other USB port I had hooked in a 4 port USB hub without an external power source. On that hub I was running a mouse and a Nostromo Game Pad. When I started using this setup up, I started experiencing hard freezes while playing Skyrim. I knew the issue was most likely that the single port could not handle these two devices without an external power source on the hub.

I moved my Windows Steam folder off the external drive onto my C drive, then I was able to ditch the external drive when running a Steam game. The Nostromo plugged directly into one of the USB ports, the mouse into the other USB port. Issue solved, FYI. :)
 

lostless

macrumors 6502
Oct 22, 2005
347
6
A USB can only handle up to 500mA. 1 hard drive if not powered can easily eat that up and cause problems as the port can not power everything on that bus.
 

Huntn

macrumors demi-god
Original poster
May 5, 2008
17,060
16,567
The Misty Mountains
A USB can only handle up to 500mA. 1 hard drive if not powered can easily eat that up and cause problems as the port can not power everything on that bus.
So it could be a stupid question, but do 2 USB ports feed into the same place on a laptop or can each one handle 500mA? Thanks!
 
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Huntn

macrumors demi-god
Original poster
May 5, 2008
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The Misty Mountains
Each port can handle 500mA. On a powered hub each port gives you 500mA.
I would have thought one port then could handle a mouse and a gamepad... admittedly I don't have a clue how much each of these devices draws (Trackball Explorer, Razer Nostromo Gamepad) :confused:
 

hchung

macrumors 6502a
Oct 2, 2008
689
0
I just had an experience where I was running an external hard drive on one of my two USB ports on my MBP. On the other USB port I had hooked in a 4 port USB hub without an external power source. On that hub I was running a mouse and a Nostromo Game Pad. When I started using this setup up, I started experiencing hard freezes while playing Skyrim. I knew the issue was most likely that the single port could not handle these two devices without an external power source on the hub.

I moved my Windows Steam folder off the external drive onto my C drive, then I was able to ditch the external drive when running a Steam game. The Nostromo plugged directly into one of the USB ports, the mouse into the other USB port. Issue solved, FYI. :)
I'm guessing the problem was actually that you had Steam on a USB drive...
 

lostless

macrumors 6502
Oct 22, 2005
347
6
I'm guessing the problem was actually that you had Steam on a USB drive...
I agree, USB asks the CPU every time it reads or wrights. USB isn't a constant stream of data. It comes in bursts and the computer may have had trouble keeping of with the data flow off the drive for the game.
 

Huntn

macrumors demi-god
Original poster
May 5, 2008
17,060
16,567
The Misty Mountains
I agree, USB asks the CPU every time it reads or wrights. USB isn't a constant stream of data. It comes in bursts and the computer may have had trouble keeping of with the data flow off the drive for the game.
I always assumed once the standard game loads into RAM, it only jumps back to the home folder when it has something to save or something it needs to add, like walking into a new area. Of course in Skyrim, the see-that-mountain, climb-it game, this could be happening quite often. :)
 

modfaith777

macrumors newbie
Jan 30, 2011
2
0
I just had an experience where I was running an external hard drive on one of my two USB ports on my MBP. On the other USB port I had hooked in a 4 port USB hub without an external power source. On that hub I was running a mouse and a Nostromo Game Pad. When I started using this setup up, I started experiencing hard freezes while playing Skyrim. I knew the issue was most likely that the single port could not handle these two devices without an external power source on the hub.

I moved my Windows Steam folder off the external drive onto my C drive, then I was able to ditch the external drive when running a Steam game. The Nostromo plugged directly into one of the USB ports, the mouse into the other USB port. Issue solved, FYI. :)
 

james_c_1

macrumors newbie
Jun 22, 2015
16
13
No problemo. If I'm reading this wiki article correctly it looks like they have the same power, but 3.0 has faster transmissions speeds. But maybe I'm not. :)
USB 3.0 ports come in low-power and high-power variants, providing 150 mA and 900 mA respectively, while simultaneously transmitting data at SuperSpeed rates.[28] Additionally, there is a Battery Charging Specification (Version 1.2 – December 2010), which increases the power handling capability to 1.5 A but does not allow concurrent data transmission.[25] The Battery Charging Specification requires that the physical ports themselves be capable of handling 5 A of current[citation needed] but limits the maximum current drawn to 1.5 A.
 
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