If you’re like many people, you’ve been slowly but surely accumulating media on your computer. Maybe you have 4,000 digital photos sitting in folders on your desktop, or maybe you’re a hardcore music collector who has been downloading from iTunes like a fiend. Either way, that media takes up precious space on your computer and needs to be stored properly — external hard drives can take care of that. Here’s what you need to consider before you buy an external hard drive.

Why You Need One

Leaving your content on your computer without backing it up is a no-no for several important reasons. For one thing, it slows down your computer. And for another — and this is crucial — you run the risk of losing everything in the event of a hard-drive crash. Don’t say it won’t happen to you because I bet you know at least one victim to this scenario. I know I do.

Even a relatively small external drive will be able to tide you over for quite some time if you’re just a small-time media collector.

Type

There are generally two types of external hard drives: solid-state drives (SSD) and hard disk drives (HDD). Solid-state drives, although extremely fast, are also extraordinarily expensive. You can pay nearly triple that of an external HDD when you start getting into large capacities. Although an external SSD is safer because it has no moving parts, you should be OK with an HDD as long as you don’t treat it like a maraca when you’re transferring files.

If durability is truly a concern (i.e. you travel a lot), look for a drive that boasts “ruggedness.” These drives often have a reinforced exterior for added protection.

Size

How much is enough? Well, this will depend on how much you have. If most of your files are word-processing documents and spreadsheets, you won’t need the biggest box on the block. 250GB or 320GB will last you quite some time.

If you have an extensive music or movie collection (and you don’t plan on quitting your download habits anytime soon), bigger is better. Prices have dropped so much on external storage that there’s no harm in getting a 1TB or 2TB drive.

Security

Some drives just act as storage boxes; they’ll hold your data and nothing more. Others provide some measure of extra security, whether it’s automatic backup or file retrieval. These features typically cost extra, so it’s up to you whether you want to spend the money for the peace of mind they’ll bring.

Speed

When talking about speed (how quickly it takes for the drive to read and write files) most drives are either USB 2.0 or eSATA devices (and, rapidly coming, USB 3.0 ). If you have a Mac, you might be interested in drives with a FireWire connector.

eSATA is faster than USB 2.0 but it typically requires an external power source, so you’ll be plugging the external drive into an outlet as well as into your computer. If you’re going to be transferring large files (i.e. high-definition movies), this might be worth your while.

Networkability

If you’re a solo computer user, you can usually get away with a simple external hard drive. But if you’re a small-business owner or you have multiple computers in your house, you should look into getting a network-attached storage device, or a NAS. These are, simply speaking, external hard drives with very large capacities that can automatically back up several computers.

They cost more than the bare-bones external hard drives — sometimes much more, depending on the size and how many computers you plan to back up — but they are invaluable devices if you’re running on multiple computers.

Final Warning

Remember: It costs much less to back up your data now than it will to pay a company to try to retrieve it later. And paying a retrieval service is no guarantee that you’ll get back what you’ve lost.