Re: usb hard drive question

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"rb" <rbig@xxxxxxxxxxxxx> wrote in message
news:Od%235rviNJHA.1896@xxxxxxxxxxxxxxxxxxxxxxx
How well do the usb hard drives that are powered from the USB strip work?
I see a lot of 'em are this way, now.

It's actually the case, not the drive, you are referring to. You can buy
excellent cases starting around $25 and then use your choice of hard disk.
It takes minutes to set up. You can also buy cases that support multiple
hard disks with RAID and FTP functions and that have Ethernet ports.

There are two types of case. One has a separate AC power adapter, and
these are usually used with desktop-sized (3.5") hard disks.

The other type uses a special cable with three ends. Two of the ends attach
to USB ports, and one attaches to the drive. This is most often used with
laptop-size drive cases, and works well.

The three ended cable is necessary because a hard disk often draws nearly a
full amp of power.

In fact I've got a damaged 160 gig SATA laptop drive in front of me, and
it's rated at one amp. A couple of desktop drives in my desk drawer draw
about .75 amps at 5v and .5 amps at 12v (desktop drives use both voltages,
while laptop drives use only 5v).

USB ports, by spec, can provide no more than *half an amp* - 500m, so a
single port cannot supply enough power for these drives.

If you try to run a one-amp hard disk off a half-amp port, you won't have
positive results. Usually the protective circuitry shuts down the port
before damage is done, but you aren't likely to be successful. You may
have to shut down the machine and reset the BIOS to get the port back.

This also means that if you attach such a drive to a passive USB hub - one
that does not have its own power adapter - to one system port, you'll draw
too much power and the port will crash, at best. When purchasing powered
hubs, it is important to look at the power rating of the adapter. It has
to be over an amp.

HTH
-pk


.

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