The first external hard drive I bought was a 60MB (yes, megabyte) drive for my Macintosh SE back in 1987. The drive wasn’t cheap, which is why external hard drives really weren’t that popular for a long time. Today, however, you’re really being silly if you don’t get your PC an external hard drive. Here are my thoughts on the topic.

There are four things to look for in an external hard drive:

• Capacity
• Cost
• Portability
• Interface

A fifth factor is Macintosh compatibility, though when you’re a Mac owner you’re used to confirming that a product is “Mac compatible.” Only a few of the higher-capacity external drives seem to lack Mac compatibility.

Capacity. Capacity is the amount of information the external hard drive is capable of holding. The more, the better. In fact, for backing up your PC I highly recommend getting an external drive that matches or exceeds your PC’s internal hard drive capacity. Preferably, get an external drive that has double the capacity of your computer’s main hard drive.

For today’s hard drives, capacity is measured in gigabytes (GB) and terabytes (TB), billions and trillions of characters of storage, respectively. But the values given are not the same values used to measure computer memory. For example, 1GB of hard drive storage is 1,000,000,000 bytes of data, not the “true” binary value of 1,073,741,824. So when Windows or Mac OS tells you that your 500GB drive actually stores about 465GB of data, don’t feel like you’ve been ripped off.

Cost. I’m not saying “price” here because the bottom-line dollar figure on a hard drive isn’t the number you’re supposed to be looking at. Instead, consider the cost as in dollars-per-gigabyte. That’s a bang-for-the-buck value, with the bang being GB of storage and the buck being, well, not what it once was. Obviously the more storage you can buy per dollar, the better value the drive.

For example, which is cheaper, a 300GB drive that costs $65 or a 500GB drive that costs $103? Our culture has most likely trained you to believe that the $65 drive is cheaper. It’s not. The $65 drive costs 21.6¢ per gigabyte of storage. The $103 drive cost 20.6¢ per gigabyte, which makes it a better value, and a better choice.

Portability. It may seem like portability shouldn’t be an issue with an external drive. By definition, an external drive is “portable” in the sense that it doesn’t weigh 40 lbs. More importantly, some drives are designed to be portable, such as the popular Passport series. The intention is that you can take your work with you wherever you go. They are external laptop drives.

A portable drive will cost you more money, but the price is worth it. Another bonus: the portable drives take advantage of USB power, so you don’t need to lug around a power brick and extension cord to make the drive work. (Then again, if you don’t need that much storage, get yourself a high-capacity media card and use it instead of an external drive.)

Interface. The interface is the way the external hard drive connects to the computer. The most popular interface is Hi-Speed USB, which is what I recommend. You can also find IEEE 1394 or “FireWire” drives, but I’ve not had a good run of luck with them. Some of the pricier external hard drives sport both types of interface.

A plus to consider is an external drive that sports additional USB or IEEE connectors so that you can daisy-chain more drives. Some external drives have this feature, many do not.

If you don’t already have an external drive attached to your computer, get one now! With today’s handy backup programs, there is no reason not to add an external hard drive to your computer’s hardware inventory.