Choose the right USB hard disk

This is the first of two articles on how to choose high-capacity storage products. Here we look at external hard disks that connects to a PC by USB. You can also read our guide to choosing a network attached storage (Nas) device.

How much storage space do I need?
Everyone’s storage requirements are different but in general it pays to buy the highest-capacity disk in your price bracket. There are three reasons:

•    Higher capacities offer much better value, as we will show.
•    The kinds of files that people are storing these days tend to be larger – extensive photo collections, the family music collection and higher-quality videos.
•    You get more flexible backup options from larger drives. Having more than one copy of files you would hate to lose is important.

Many external hard disks that attach to a PC via USB 2 are measured in gigabytes, with capacities of 320Gb and 500 Gb the most popular. Most are small enough to fit in a pocket and cost less than £50, and so are suited to people who need to carry files around.

But larger disks offer better value and greater flexibility. It’s not uncommon for new PCs to be sold with internal hard disks of 500GB to 1 terabyte (TB), so those cheaper discs can’t provide a simple way to back up files. Plus, with many households now owning more than one PC, backing up files for multiple users requires more space.

To give you an idea of how various types of files consume storage space, a 1TB drive could hold:
•    18,000 albums in high-quality MP3 format
•    More than 200 movies ripped from DVD around 1,200 film-length Xvid files
•    High-definition (HD) video, however, takes up far more space. An hour of raw footage may take up 45GB, and projects can consist of more than the 20 hours of HD footage that would fills 1TB.

How much will a larger hard drive or Nas cost?
The good news is that higher-capacity drives do not cost much more than those offering lower amounts of storage. A useful way to work out value is to divide the price of the disk by its storage capacity to give the rough cost-per-gigabyte.

For example, at the time of writing, Dabs’ cheapest 500GB drive was the Seagate Barracuda Sata-600; at £41.98,

So: 42 / 500 = 0.08p

This gives us a cost-per-gigabyte of 8p. That is not bad, but it is considerably higher than the 3.5p per gigabyte of the Seagate 2TB Barracuda Sata 6Gb/s. It costs more at around £70, but has four times the capacity of the 500GB drive, for less than twice the price.

The cost-per-gigabyte figure is lowest for 2TB and 3TB disks, since they are the ones in greatest demand and so manufactured in the greatest numbers, although 4TB disks are becoming more popular and prices have begun to fall.