Build an external hard disk

If you decide to replace your computer’s existing hard disk with a larger model, that needn’t render the outgoing hard disk redundant. As long as the drive being replaced still functions correctly, it can be usefully recycled into an external USB drive. For both laptop and desktop PCs, the process is simple and, beyond a set of basic tools, the necessary equipment costs just a few pounds.

In this Build It article, we’ll explain how to recover an old hard disk and fit it into a special case that will allow it to be used as a USB drive that will attach to almost any modern computer.

Read more: Hard disks | How to

Why build a USB hard disk yourself?
Assuming the reason for replacing your computer’s existing hard disk is to gain space rather than fix a fault, the end of the process will leave you with a spare hard disk - probably containing all your old files.

Buying a new external enclosure for this old drive will not only give it a new lease of life but an external disk is one of the most useful things you could own – think of using it to back up your My Documents folder, or as an alternative to toting folders full of pictures around to relatives’ houses.

What you will need
Fundamentally, this job is about taking an internal component out of your computer and putting it in a case that will allow it to survive in the outside world. Hard disks are susceptible to vibration and impact damage so you need to install an old drive in a case (often called an ‘enclosure’ or ‘caddy’) to protect it. This is especially important for laptop hard disks, which are more likely to be transported.

The enclosure will convert the hard disk’s power and data connections – designed for your computer’s internal wiring – to connectors that will allow you to plug your disk in to both the mains electricity (in the case of desktop PC hard disks), and your computer’s external USB sockets.

The good news is that the only thing you need to buy for this project is an external hard disk enclosure, and these can be very cheap. Exactly what type of enclosure you need depends on what kind of computer your old hard disk is coming from.

Most desktop PCs use 3.5in-sized hard disks – that is, hard disks whose internal data-storing platters have a diameter of 3.5in. Laptop computers, which have restrictive size and power requirements, generally use 2.5in disks. The upshot is that you need a larger hard disk enclosure for a desktop PC than you do for a laptop.

If you’re not concerned about looks or features, an enclosure can be had for under £15. Dabs, for example, offers a 2.5in enclosure for £4, while 3.5in enclosures are only a little more expensive (see this £13 model from Amazon). Either of these will be adequate for protecting your disk and allowing it to connect to your PC.