External Backup Drives

“Should I buy an external backup drive” is one of the most common questions I am asked by my computer support clients

My answer is usually “yes”, because the question implies that the client is not backing up anything at the moment. The next question is, of course, “what should I buy?”

The main considerations are these:

Form Factor

Western Digital 3.5 inch external drive
Western Digital 3.5 inch external drive
External drives are either 2.5 inch or 3.5 inch. This is a measure of the width of the drive itself (not the housing in which it is contained). Functionally, the two sizes are the same. The physical size of the entire unit in its housing is, however, quite different. If you think you might want to carry the drive about with you then the smaller size would be more suitable. Apart from physical size, the other main difference is that 2.5 inch drives are usually powered via the USB connection, whereas 3.5 inch drives have their own power supply. This might make them slightly more reliable, but it does, of course, mean that you need to find yet another power socket within reach.

At the moment, capacity ranges from about 340gb to 3tb. A “tb” is a “terabyte” – ie 1000gb (gigabytes). So, the 340gb is approximately 1/9 the size of the 3tb. You might like to look at the comments I made on hard drives in this post on buying laptops as they also apply to buying an external drive for backup purposes.


USB3 port
A USB3 port, distinguishable by being blue inside
Connection to the computer is via either a USB2 or USB3 port. Drives with USB3 connections transfer data much faster then USB2 connections provided that the computer at the other end also has USB3. If it doesn’t have USB3 then transfer happens at the lower USB2 speed. I would definitely recommend buying a drive with USB3 even if your current computer does not have USB3 – your next computer will have. You can, by the way, always tell a USB3 connection as it is blue inside (as opposed to the black of a USB2 connection).

Rotation Speed

Different discs rotate at different speeds. 5400 rpm is a typical speed. Faster spin speeds result in faster data transfer rates but there are other factors that affect how fast a drive performs, so the “rpm” figure is not necessarily all that significant.

Backup Software

These notes about backup software are for Windows PCs only. Although the drives themselves are compatible with both Macs and PCs, backup strategy is different. If you own a Mac then you would undoubtedly use the external drive with the Mac’s inbuilt “Time Machine” software. This is much better and simpler than any backup software ether built into Windows or provided on an external drive.

However, if your are a PC owner it may be important for you to make sure that the drive you buy has its own inbuilt backup/restore software. This is usually fairly easy to set up to perform automatic incremental backups of data files in standard locations. This may need a bit of explanation:

  • “automatic” – the backups are automatically created according to a user-defined schedule.
  • “incremental backups” – files are backed up (according to the schedule) after they are first created (or, more precisely, when they are first saved), and also every time they are updated (ie when they are saved again).
  • “standard locations” – some software will only back up data files that are located in the “Documents” or “My Documents” folders (and their sub-folders). In other words, the software may or may not be configurable to back up files saved in other locations.

When it comes to backups, the devil tends to be in the detail. The principle is fairly easy – backups are copies of files that you create as potential replacements for lost, deleted, or damaged files. However, there are many types of backups, many different scheduling possibilities, many sorts of backup media, many different storage strategies and so on. My experience of many years with my computer support clients is that it is better to have a simple backup strategy that you actually carry out, than a complicated one that you don’t. The simple solutions provided with external drives are usually fairly quick to set up and are undoubtedly better than no backup at all provided that you normally save your data files in the default areas within “My Documents”.

Please note that this blog post is a general guide only. I am not promising that any specific software performs any specific backup task. You are urged to check the results of taking backups so that you can be fairly confident that the procedure works.


Seagate 2.5 inch external drive
Seagate 2.5 inch external drive
Larger drives tend to offer better value in terms of price per gigabyte, but it could be false economy to buy a 3tb drive if you will never use it. 500gb drives start at about £50.

As a very rough guide, if you rarely or never store movie/video files, music files, or very large numbers of photos in specialised formats (such as RAW or TIFF) then a 500gb is probably going to be plenty large enough. If you take a lot of photos, or have an increasing music and/or video collection, then maybe a larger drive will be better.

So, in conclusion, if you are thinking of getting an external drive for backups purposes, then do it! I have seen for myself just how upsetting and disruptive it can be to lose data completely. Any backup is better than no backup.

(Last updated 08/09/2023)