Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Old April 7th 10, 04:22 PM posted to rec.crafts.metalworking
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Default Anyone have an External Hard drive available?

On Apr 6, 8:30*pm, wrote:
On Tue, 06 Apr 2010 11:29:58 -0700, sittingduck

wrote:
Michael A. Terrell wrote:


* *Where do you think those front panel USB ports go?


Stupid question, don't you think?
To a long wire that connects to some pins on usb headers.
They are typically weaker than the regular usb ports.


The USB port supplies a maximum of 500ma per port at 5 volts. The wire
is mabee a foot long - so total 2 feet of *conductor. SAY it is 28
guage. Resistance is 212 ohms per KM, or *0.0054359 ohms per inch 0r
roughly 0.13 ohms for the 2 foot assembly. Voltage drop under full
load is 0.13X.500= 0.065 volts.

That's 32 *milliwats of power loss.
Totally inconsequential in my books.


If you're REALLY lucky, the MB USB ports will supply half an amp
each. The VIA chipsets aren't in compliance with the spec, NVIDIA is
marginal, the only MBs I've had good luck with USB-powered accessories
are ones with Intel chipsets and they're the ones that originated the
spec. If it's not an Intel-based MB, I get a separate USB port card
with an NEC chipset on it, hook the case USB sockets to that and
disable the MB ports. Items like the larger capacity portable USB
hard drives and port-powered scanners just can't get enough juice out
of the wimpy ports, have fought the battle many times. USB cards with
other make chipsets aren't compliant, either. Some hubs won't make
the grade, even with external wall warts. The consequences of pulling
more current than the port can supply range from the machine shutting
itself off to the port shutting off until reboot to the OS just not
recognizing the device when it's plugged in. With USB-powered hard
drives, marginal current supply will result in the drive dropping off
and adding back in repeatedly, if it happens while a file is being
moved, the file can disappear and the drive can go corrupt. If all
you use the USB ports for is the occasional flash drive and mouse and
keyboard use, you'll not have a problem.

As far as front vs. rear ports, I've noticed the same on some
machines, sometimes the front ports are the early 1.2 spec and only
the rears are 2.0. Depends on how cheap the OEM was. You'd think by
now that everyone would be putting in 2.0, at least, but there's still
1.2 devices and ports being sold on new equipment. Must be a bunch of
1.2 interface chips in some Taiwan warehouse somewhere and they need
to dump them somehow, particualrly now that v3 devices are out now.

I've also found there's a vast difference in the cables used to link
devices up to ports and hubs, too. Some have enormous voltage drops,
sometimes just swapping the cable enables the device to work. Has no
relation to price of the cable, either.

Stan

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