2 May
2011
2 May
'11
11:17 p.m.
On Mon, May 2, 2011 at 3:19 AM, Hakan Koseoglu <hakan(a)koseoglu.org> wrote:
On 1 May 2011 18:51, Mark Knecht
<markknecht(a)gmail.com> wrote:
Hi Hakan,
OK, so I guess obviously the USB port must supply some amount power or
even a simple flash drive wouldn't work as the memory in it has to
require some sort of +/- supplies to function at all.
In terms of my external USB hard drive, I have 3 like the following
link except mine are 500GB.
http://www.amazon.com/Buffalo-Technology-DriveStation-External-HD-CX500U2/d…
This drive ships with an external wall wart power supply and doesn't
function without it on any machine I've plugged it into.
I think what I've going to do is drop by Guitar Center and see if they
have any open devices they will allow me to plug into my laptop, just
to see if they are recognized at all.
Cheers,
Mark
As far as I can tell, no, I don't. I own a
couple of USB hubs and 4
external hard drives. None of them functioned at all when attached
without their power supplies.
According to the proper USB1/2 specs, you're
only supposed to feed
0.5A at 5V (a measly 2.5W!) to an individual port. Now, most USB
chipsets don't have the necessary hardware to achieve this and will
provide up to 2A for a bus of four, letting any device draw as much
current as they require (10W!). Most hard disks, on the other hand,
will require more than 0.5A at 5V. Thus if you have a compliant
machine, they won't work. If you have a dodgy machine with no
isolation between the USB devices, it's more likely to work! Hubs
without their own power supply draw the power from the mother board,
making the power issue even more of an issue (4 devices served by a
0.5A current source).
All of this means that since none of your hard drives works, your
machine has a good, proper implementation of the spec with isolation
between individual ports plugged into the same internal bus. Also it
means any device that's completely broken in power requirement will
struggle.
Even different machines from the same manufacturer has issues. My Dell
laptop can't drive one of my disks but a Dell PC can.
USB3 has increased the individual current amount to 0.9A at 5V (4.5W).
Most likely the implementation will be broken and a whole pile of USB
powered devices will arrive soon, drawing massive amount of power
(18-20W?).
--
Hakan (m1fcj) - http://www.hititgunesi.org