I am looking for an automatic external backup hard drive, connected and powered by USB only, with no power plug but which can be used for more than one computer. i.e the hard drive should be able to be connected and regonise Computer A and back up any updated files and then when I connect Computer B it will regonise computer B and back up any updated files ETC.
Is there a model which does that?
Thanks.

1. you have a problem with the power source - and may use therefore 2,5" drives in an external case only
- maximum capacity is available up to 500gb - and some 600 or 750gb drives should be allready around.
I am not sure, whether such drives would run powered by usb power only ....?
The 250gb or 320gb (Samsung) do work+

2. The back up is simple to organise with any good back up software which allows to define scheduled back up operation.
Install the software on both computers - define on each pc a new back up process, make a full backup of complete pc
- and define a schedule for back up at specific time for incremential back up.

I would make two partitions, one for pc a, one for pc b - define the back up time for a in the morning, the back up time
for b in the evening. If a back up is lost - on most back up softwares you are able to define automatic back up - if a
scheduled back up was missed.

Not to forget that the back up procedures of pc a and pc b should have different process names.

simple - but needs disciplined user - didnt meet one yet - even not me

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If you need a kind of automatic back up whenever you connect the external drive - try
Allway Sync (freeware) at www.alwaysync.com

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