If you've upgraded your laptop or PC with an SSD, you're probably wondering what to do with the old hard drive. For little money, you can install it in an external enclosure and use it as an external USB drive. Here's how.

Can an internal drive be used externally?

Yes. Hard drive caddies - or enclosures - are effectively SATA-to-USB converters and allow you to turn an internal SATA hard drive into an external one that you can use for storing or backing up files, or to keep a library of videos that you could leave attached to your TV.

A quick word of warning, though. If your hard drive is old, it's unwise to use it for backing up important files as hard drives have a limited life span. You'll be doing well if your hard drive is still going after five years, but it is a high risk to entrust photos and any other files you can't replace to an old drive. It's best to buy a new one, or buy a portable USB drive which is less hassle, or ensure you make several backups on different drives - and the cloud - for better protection.

Assuming your drive isn't ancient and is working well, you'll need to buy the appropriate external enclosure. There are two main types: 3.5in and 2.5in.

3.5in hard drives are mainly used in desktop PCs, while 2.5in disks are used in laptops. Laptop hard drives vary in thickness (either 7mm or 9.5mm), so make sure your chosen caddy has enough height inside to accommodate your disk.

We're using a 9.5mm drive here and an Inateck USB 3 enclosure, which you can buy for £11.99 from Amazon and will accept both 9.5mm and 7mm drives, including SSDs as well as traditional hard drives. If you're in the US, it's even cheaper at just $7.99 from Amazon. There's also a USB-C version if you'd prefer to use the latest USB standard.

USB-C ports are slowly becoming the standard and you'll find these on the latest laptops and PCs.

Aukey sells a USB-C enclosure that you can buy for £12.99 from Amazon UK and $13.99 from Amazon US.

Aukey USB-C external enclosure

Theoretically the USB-C connection on this caddy can operate at up to 5Gb/s or 625MB/s, but it will be limited by the hard drive you put inside it.

Most hard drives use a SATA connector (you can see this in the photo below), but so make sure you buy an enclosure which is compatible with your drive. 

How to install a hard drive into an external enclosure

1. If you haven't already done so, remove any brackets and screws from the hard drive.

How to use a spare internal hard drive as an external hard drive

2. Open up the caddy: the Inateck FE2005 we're using is a tool-less model, so it's a simple case of unlocking it with the switch, sliding open the end and inserting in the hard drive. Be careful to slide the hard disk in the right way up - look inside to see the orientation of the SATA port.

How to use a spare internal hard drive as an external hard drive

How to use a spare internal hard drive as an external hard drive

3. Use the included USB cable to attach the enclosure to your PC or laptop.

4. Depending on what's on the disk, it may show up in Windows File Explorer and be ready to use. Because our disk was from a Windows laptop, it was formatted as NTFS and was assigned a drive letter automatically.

You can treat it like any hard drive, copying files to it, or formatting it. If you plan only to use it with Windows, you can leave it formatted as NTFS, but it's best to use exFAT if you want to connect it to other devices such as set-top boxes for video playback.

What you might not want is for the drive to show up as two disks, as ours did due to a 100MB system partition from the old Windows installation.

We'll deal with this in the next step, which also applies if your disk doesn't appear when you connect it.

How to use a spare internal hard drive as an external hard drive

5. If it doesn't show up in Windows Explorer, search the Start menu for Disk Management and then look for a disk with unallocated space, or a disk without a drive letter assigned. You can then right-click on it and format it.

How to use a spare internal hard drive as an external hard drive

If, like us, you need to remove an unwanted 'System Reserved' partition, just right-click on it and choose Delete Volume. It will then be unallocated space, and since it's only 100MB, we will just leave it unused.

How to use a spare internal hard drive as an external hard drive