The first landmark isn't one that will necessarily trigger any alerts, and occurs when your drive nears 90% of its capacity. Having acknowledged that this isn't just a problem for MacBook Air owners with a paltry 64GB of drive space, what are the tell-tale signs that your drive might be starting to reach its limits? It's therefore obvious that even the largest hard drive can quickly become overwhelmed with all those files you've been copying to it.

You might also be surprised to learn how many duplicated files exist on your hard drive - it's bad enough having two or three copies of a file, but when that file is a 10GB movie you can quickly see how it is that the hard drive that looked virtually bottomless a few months ago is suddenly full to the brim. It doesn't end there either: your iTunes library can consume more than its fair share of space, what with your music collection, podcasts, movies and TV shows to handle.

The average one hour HDV tape holds 13GB of data, so it doesn't take long to gobble up hundreds of gigabytes with your original footage, never mind the final edited movie. It's even worse when you look at all the camcorder footage you've got stashed away. That equates to anything from 400MB to 1.5GB for every 100 photos on your hard drive. Today's high resolutions come at a price - every 10-megapixel photo consumes around 4MB in JPEG format, or up to 15MB in raw format. The biggest drain on your hard drive will, however, be your personal files, and specifically all those photos and videos you've uploaded from your brand spanking new camera and camcorder. All well and good, but yet more gigabytes of precious drive space have gone in the meantime. Again, it's easy to let them just pile up on the off-chance you might need them at some unspecified point. Next, there are all those files you've downloaded from the internet via your browser, or received as email attachments. That can account for a few gigabytes of space easily, but it's only the tip of the iceberg.

The likelihood is you've installed a fair few applications, some of which you were trying out and forgot all about during those heady days when you thought that space would last forever. The first thing to understand is how your hard drive has become so full.

How to clean up macbook air hard drive