Why do powered external drives still exist when you can easily use a USB one?

I'm trying to understand the advantage of the old style external drive e.g. Western Digital My Book, which needs to be powered separately from the computer, compared with external drives that are powered by USB.  If they both perform the same function, why bother with the old drive if the computer can sufficiently power the drive with less cables and mess and furthermore lack of a need for a power socket?
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dbruntonQuid, Me Anxius Sum?  Illegitimi non carborundum.Commented:
If ...

A USB 2.0 port can supply 5 volts at 0.5 amps.  That's 2.5 watts.  You can get hard disks that can operate on that power supply, typically 2.5".  And you can get hard disks that won't, typically 3.5".  You've also got port sharing which can cut down on the amount of power available.  

So if you want to ensure reliability you supply an external power supply with your external hard drive.

Some early external USB 2.5" drives came with 2 USB connectors.  One was data and power and the other was plain power.  On many computers the data and power cable was sufficient.  On others you had to use both cables.
u587162Author Commented:
Would that explain possibly why when I add a non powered 4-port USB hub to my single port USB laptop (surface book pro 3) and add my external seagate drive to it, it works fiine but them moment I do any large ftp'ing, I get a connection and disconnection notification?  As if unplugging the USB and reconnecting it again?
dbruntonQuid, Me Anxius Sum?  Illegitimi non carborundum.Commented:
Quite possible.

The laptop might be at the limits of what power it can supply and under load power to the USB ports is flaky.

If you try a powered USB hub and the problem doesn't exist then the above scenario would probably be correct.
noxchoProduct ManagerCommented:
Answering your first question: because sometimes the usb ports do not give enough power to some drives. Bear in mind some drive enclosures need more energy than others. Plus with the time the usb ports start giving less power. Depends on how intensive the usage is.
And answering your second question: yes, this is pretty possible, because the power usage increases when the drive is actively used.
Tom CieslikIT EngineerCommented:
Regular 3,4" drives require 12V for motor and 5V for electronic that's why you need separate power supply. Small HDD drive 2.5" need only 5V to operate because small motor inside is powered by 5V supply.
If you connect HDD through USB hub sometime you can get disconnection notice since HUB is using a part of power coming from USB and after while electronic board in HDD starts loosing connection since there is not enough power to supply it

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Some laptops, even if the power for USB ports is defined, just can't deliver that amount. They just don't have the circuitry to supply enough power. Besides, laptops are often built to conserve power, so having to supply it to external devices isn't the best option.
JohnBusiness Consultant (Owner)Commented:
I use only USB powered external hard drives now. Not worth trying to power them in every situation. I abandoned that.

The only USB Hub I have (home office desktop) is powered and there is no issue connecting through that or keeping connections.

I simplify as much as possible.
If your laptop has USB 3, then you likely won't have power issue on the USB 3 ports.  The USB 2 ports don't always supply enough power, depending on how many items are on it.  Some laptops have both USB 3 and USB 2 ports, and those are generally color coded with blue as USB 3 and usually black as USB 2 when you look into the ports.  Plug your external 2.5" USB disks into a USB 3 ports and you'll never have a power issue, even if your external disk is only USB 2.
or use a powered usb hub, if you're working on USB 2 - that's what i Always do
u587162Author Commented:
It's because I only have one USB 3.0 port on my Surface Pro 3 and I was using a 3 port hub plugged into the port due to other devices I also need to connect, that I raised this question.  Plugging the drive directly into the single hub does not given me that problem.
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