QUESTION I will soon be buying an external hard drive and I need some advice. I rather like the idea of a portable USB-powered unit, but are these as efficient as a mains-powered unit? It will be used only to store my photos and music, so it won't be in continuous use. (See all Storage Reviews.)
HELPROOM ANSWER: External hard drives are a great idea, both for essential backups and to expand the total amount of storage available to you.
The type of drive you need will to some extent depend on how much storage you require, but also whether you need a
high-speed external drive. USB-powered drives are convenient as they don't require an external power supply – you can use them on the fly when connected to a laptop.
A disadvantage of USB-powered devices is that some PC USB ports don't deliver enough power to operate the drive.
Some will come with a USB Y-cable, which allows you to simultaneously plug the drive into two USB ports. It will use only one port to transfer data, but both for power. This is a problem only if you don't have two spare USB ports.
If your PC has a USB 3.0 port (or you will be upgrading it any time soon), you might like to buy a faster USB 3.0 drive. A single USB 3.0 port will likely have enough power to operate the drive, but keep in mind that you may run into power issues if you ever need to connect the drive to a system that has only USB 2.0 ports.
Many USB-powered hard drives can be used with an external power supply, which is usually purchased separately. Sometimes, if your drive is of the type with twin USB connections, you can hook up the one designated for auxiliary power to a USB phone charger.
Going for USB 3.0 also makes sense because it can achieve much faster transfer speeds than USB 2.0. Even if you don't have any USB 3.0 ports on your PC now, you're likely to have them on your next system.
For maximum portability you can go for a drive with a 2.5in laptop hard disk inside, but if you need to store more than a terabyte of data you'll have to go for a larger desktop model with one or more 3.5in disks. Apart from being larger and heavier, these drives will almost certainly require an external power supply.
The USB interface is often the limiting factor in terms of performance – unless you go for an SSD, which will be faster, but more expensive and with reduced capacity.