I can't neither confirm or deny, but I know that mobo can only supply
certain amount of power to all USB ports (that connect to it).  If I still
remember the number, it is 500ma (correct me if I'm wrong), which you can
see is not much at all. So that any USB device that requires USB port to
supply power, will use part of the total supply, if the total is greater
ther 500ma, you may not add more USB devices unless they have their external
power supply (eg. via power adapter).  Most powered USB hub can supply
5000ma power to all its ports. that's one of reason why all USB hubs should
be powered, none powered USB hubs are normally useless.

Power requirement is an important part that you will never see on ad, or
never told by sales persons who try to overwhelming you, but it is one of
the most common USB problem. (8, 10 or more USB ports won't make any sence,
if you can't find all the power required by devices, sadly, these days, more
ports sounds better regardless if they work together or not)

Most USB mice use 100ma (eg. my optical mouse), my USB powered scanner uses
500ma, my web camera uses 100ma, so in my case (my usb devices require 700ma
if they work at once, but my mobo can only supply 500), I know that if my
scanner is running, I couldn't use my camera (mouse still works).

Jun Qian

----- Original Message -----
From: "A&C Thompson" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, June 17, 2002 6:06 AM
Subject: Re: [PCBUILD] USB hub theory (Brenda Dencer)


> If memory serves, "every other" hub must be powered via AC. So a usb
connection on the PC will be
> powered, but the first external hub after that shouldn't need to be, and
the next will need to be,
> and so on (up to 127 devices total - not hubs).
>
> I'm wondering if the 2 ports on the PC work the same way - is it possible
one is powered and the
> other is not?
>
> The following is just a theory - the port you plugged the hub into *may*
be the # 2 port, (port 1 is
> powered so port 2 doesn't need to be). If that's the case, then your hub
would need to be powered.

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