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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