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146 Posts
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5648
February 24th, 2004 09:00
USB hard drive not working properly
my usb hard drive works fine on my home laptop, but when i plug it into the computers in college, i cant copy really large files onto it. it just says Disk IO error. could this be because my college account is not administrator and i cant copy large files or mount large drives. is this possible? when its on the pc at home also, it needs an extra power lead to work, but when i plug in a small usb hub, it works fine with no extra power lead. the usb hub plugs into one usb slot, and gets its power from another free usb port. any ideas on why it behaves like that?
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godim
507 Posts
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February 24th, 2004 11:00
A USB port can only provide 500mA of power. Most mobile hard disk require a little more (~600 -> 750 mA). This taking power from two usb ports gives 1000 mA which is enough to run these drives.
Most desktops with decent motherboards however can give up to 1000 mA on a single USB port and thus do not need such a special cable.
Do you connect to two usb ports on the college PC's as well? If not, it is powwible the USB port is just barely providing enough power which causes errors when the hdd hetas up (like when copying large file) and starts eating a little more power.
schmintan
146 Posts
0
February 24th, 2004 16:00
godim
507 Posts
0
February 25th, 2004 12:00
If the zip drive uses an adaptor it requires no power from the USB port. If it doesn't need a net adaptor it is using the full 500 mA. In this case you cannot use the external HDD and ZIP drive together.
In the other case it is indeed complicated. Some USB hubs have a build in limit that prevent them from giving more than 500 mA. In this case the hard disk will not work on it wheter you give it external power (through a net adaptor) or connect it to two usb ports. If your lucky however the hub will dynamically allocate power.
In this case you have 0 mA (zip) + 200 mA (USB hub) + 100 mA (USB key). This leaves about 700 mA for your hard disk which may be just enough.
The only way to find out though is through testing